工具除了会用，还应该多做点。我觉得使用一个软件工具（开源类），一般会经历几个步骤：
1. 通过wiki了解大致作用，然后开始码代码；
2. 系统性地学习其特性，找出可能需要的点，用上去；
3. 通过阅读其源码，清楚其来龙去脉；
4. 有能力你就去超越别人；
mybatis作为orm框架给我们带来了很多方便，其定制功能也让我们惊喜！还是来看看别人怎么做到的吧！
1. 下载git仓库, https://github.com/mybatis/mybatis-3
2. 打开IDE, 找到 test 包
3. 进入 org.apache.ibatis.autoconstructor.AutoConstructorTest, 有一个完整的sql 样例
public class AutoConstructorTest {
private static SqlSessionFactory sqlSessionFactory;
@BeforeClass
public static void setUp() throws Exception {
// create a SqlSessionFactory
try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/autoconstructor/mybatis-config.xml")) {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
}
// populate in-memory database
BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),
"org/apache/ibatis/autoconstructor/CreateDB.sql");
}
@Test
public void fullyPopulatedSubject() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
final Object subject = mapper.getSubject(1);
assertNotNull(subject);
}
}
@Test(expected = PersistenceException.class)
public void primitiveSubjects() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
mapper.getSubjects();
}
}
@Test
public void annotatedSubject() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
verifySubjects(mapper.getAnnotatedSubjects());
}
}
@Test(expected = PersistenceException.class)
public void badSubject() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
mapper.getBadSubjects();
}
}
@Test
public void extensiveSubject() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
verifySubjects(mapper.getExtensiveSubject());
}
}
private void verifySubjects(final List<?> subjects) {
assertNotNull(subjects);
Assertions.assertThat(subjects.size()).isEqualTo(3);
}
}
目标方法：fullyPopulatedSubject()，最终进行一条 select 查询：
SELECT * FROM subject WHERE id = #{id}
首先执行的肯定 setup()方法了，setup()做了三件事：
1. 加载mybatis-config文件读取到reader中；
2. 将配置文件传递工厂builder中创建会话工厂；
3. 执行hsqldb内存数据库的初始化工作；（非本文重点）
接下来，咱们从源码的角度，主要看会话工厂的创建过程！
创建 sqlSessionFactory
try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/autoconstructor/mybatis-config.xml")) {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
}
// SqlSessionFactoryBuilder.build(reader) -> XMLConfigBuilder.parse()
// org.apache.ibatis.session.SqlSessionFactoryBuilder
public SqlSessionFactory build(Reader reader) {
return build(reader, null, null);
}
// 建立factory
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
// 加载完成后，上下文管理器重置
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
标签解析：
/**
* Offline entity resolver for the MyBatis DTDs
*
* @author Clinton Begin
* @author Eduardo Macarron
*/
public class XMLMapperEntityResolver implements EntityResolver { private static final String IBATIS_CONFIG_SYSTEM = "ibatis-3-config.dtd";
private static final String IBATIS_MAPPER_SYSTEM = "ibatis-3-mapper.dtd";
private static final String MYBATIS_CONFIG_SYSTEM = "mybatis-3-config.dtd";
private static final String MYBATIS_MAPPER_SYSTEM = "mybatis-3-mapper.dtd"; private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";
private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd"; /**
* Converts a public DTD into a local one
*
* @param publicId The public id that is what comes after "PUBLIC"
* @param systemId The system id that is what comes after the public id.
* @return The InputSource for the DTD
*
* @throws org.xml.sax.SAXException If anything goes wrong
*/
@Override
public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
try {
if (systemId != null) {
String lowerCaseSystemId = systemId.toLowerCase(Locale.ENGLISH);
if (lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)) {
return getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId);
} else if (lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)) {
return getInputSource(MYBATIS_MAPPER_DTD, publicId, systemId);
}
}
return null;
} catch (Exception e) {
throw new SAXException(e.toString());
}
} private InputSource getInputSource(String path, String publicId, String systemId) {
InputSource source = null;
if (path != null) {
try {
InputStream in = Resources.getResourceAsStream(path);
source = new InputSource(in);
source.setPublicId(publicId);
source.setSystemId(systemId);
} catch (IOException e) {
// ignore, null is ok
}
}
return source;
} }
parser
// org.apache.ibatis.parsing.XPathParser.XPathParser(), 设备一些必要参数
public XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver) {
commonConstructor(validation, variables, entityResolver);
this.document = createDocument(new InputSource(reader));
}
private Document createDocument(InputSource inputSource) {
// important: this must only be called AFTER common constructor
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(validation);
factory.setNamespaceAware(false);
factory.setIgnoringComments(true);
factory.setIgnoringElementContentWhitespace(false);
factory.setCoalescing(false);
factory.setExpandEntityReferences(true);
DocumentBuilder builder = factory.newDocumentBuilder();
builder.setEntityResolver(entityResolver);
builder.setErrorHandler(new ErrorHandler() {
@Override
public void error(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void fatalError(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void warning(SAXParseException exception) throws SAXException {
}
});
return builder.parse(inputSource);
} catch (Exception e) {
throw new BuilderException("Error creating document instance. Cause: " + e, e);
}
}
// 在返回fatory的时候调用 return build(parser.parse()); 将 config.xml 的配置全部解析到 configuration 实例中
// 在返回fatory的时候调用 return build(parser.parse()); 将 config.xml 的配置全部解析到 configuration 实例中
// org.apache.ibatis.builder.xml.XMLConfigBuilder.parse()
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
// 根元素为 /configuration, 依次向下解析
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
} // org.apache.ibatis.parsing.XPathParser.evalNode() 映射 xml 属性到 bean
public XNode evalNode(Object root, String expression) {
Node node = (Node) evaluate(expression, root, XPathConstants.NODE);
if (node == null) {
return null;
}
return new XNode(this, node, variables);
} private Object evaluate(String expression, Object root, QName returnType) {
try {
return xpath.evaluate(expression, root, returnType);
} catch (Exception e) {
throw new BuilderException("Error evaluating XPath. Cause: " + e, e);
}
}
具体解析项如下，从这里也一目了然，配置项支持什么：
// 解析各配置参数到实例中
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
// 这个配置没有用过吧
loadCustomVfs(settings);
// 解析别名设置
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
// 重要节点，解析 mapper
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
下面依次来看一下都怎么解析各配置项的吧~
properties 解析
// propertiesElement(root.evalNode("properties")); url, resource 解析
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
Properties defaults = context.getChildrenAsProperties();
String resource = context.getStringAttribute("resource");
String url = context.getStringAttribute("url");
if (resource != null && url != null) {
throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
}
if (resource != null) {
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
defaults.putAll(Resources.getUrlAsProperties(url));
}
Properties vars = configuration.getVariables();
if (vars != null) {
defaults.putAll(vars);
}
// 解析完成后，放到 parser 和 configuration 实例中
parser.setVariables(defaults);
configuration.setVariables(defaults);
}
}
settings 配置项解析，返回内容待处理
// Properties settings = settingsAsProperties(root.evalNode("settings"));
private Properties settingsAsProperties(XNode context) {
if (context == null) {
return new Properties();
}
Properties props = context.getChildrenAsProperties();
// Check that all settings are known to the configuration class
MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
for (Object key : props.keySet()) {
if (!metaConfig.hasSetter(String.valueOf(key))) {
throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");
}
}
return props;
}
// loadCustomVfs(settings); 这个...
private void loadCustomVfs(Properties props) throws ClassNotFoundException {
String value = props.getProperty("vfsImpl");
if (value != null) {
String[] clazzes = value.split(",");
for (String clazz : clazzes) {
if (!clazz.isEmpty()) {
@SuppressWarnings("unchecked")
Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);
configuration.setVfsImpl(vfsImpl);
}
}
}
}
typeAliases 别名设置解析，主要做类型检查，及别名的注册工作
// typeAliasesElement(root.evalNode("typeAliases"));
private void typeAliasesElement(XNode parent) {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
// 针对package配置，需注册一系列别名，以 simpleName 代替
String typeAliasPackage = child.getStringAttribute("name");
configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
} else {
String alias = child.getStringAttribute("alias");
String type = child.getStringAttribute("type");
try {
Class<?> clazz = Resources.classForName(type);
if (alias == null) {
typeAliasRegistry.registerAlias(clazz);
} else {
typeAliasRegistry.registerAlias(alias, clazz);
}
} catch (ClassNotFoundException e) {
throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
}
}
}
}
}
// org.apache.ibatis.type.TypeAliasRegistry.registerAlias(), 具体数据结构为 map 封装
public void registerAlias(Class<?> type) {
String alias = type.getSimpleName();
Alias aliasAnnotation = type.getAnnotation(Alias.class);
if (aliasAnnotation != null) {
alias = aliasAnnotation.value();
}
registerAlias(alias, type);
}
public void registerAlias(String alias, Class<?> value) {
if (alias == null) {
throw new TypeException("The parameter alias cannot be null");
}
// issue #748
String key = alias.toLowerCase(Locale.ENGLISH);
if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {
throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");
}
TYPE_ALIASES.put(key, value);
}
plugins 配置项解析，将属性注入的plugin, 添加 plugin 到 configuration
// pluginElement(root.evalNode("plugins"));
private void pluginElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
String interceptor = child.getStringAttribute("interceptor");
Properties properties = child.getChildrenAsProperties();
// 先创建一个plugin实例，备用
Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
// 配置属性的注入，回调
interceptorInstance.setProperties(properties);
// 添加到 configuration
configuration.addInterceptor(interceptorInstance);
}
}
}
public class InterceptorChain {
private final List<Interceptor> interceptors = new ArrayList<>();
public Object pluginAll(Object target) {
for (Interceptor interceptor : interceptors) {
target = interceptor.plugin(target);
}
return target;
}
public void addInterceptor(Interceptor interceptor) {
interceptors.add(interceptor);
}
public List<Interceptor> getInterceptors() {
return Collections.unmodifiableList(interceptors);
}
}
objectFactory 配置项解析，与plugin原理相似，做替换自定义作用
// objectFactoryElement(root.evalNode("objectFactory"));
private void objectFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties properties = context.getChildrenAsProperties();
ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
factory.setProperties(properties);
configuration.setObjectFactory(factory);
}
}
// objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); 没什么特别
private void objectWrapperFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
configuration.setObjectWrapperFactory(factory);
}
}
// reflectorFactoryElement(root.evalNode("reflectorFactory"));
private void reflectorFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ReflectorFactory factory = (ReflectorFactory) resolveClass(type).newInstance();
configuration.setReflectorFactory(factory);
}
}
settings 选项解析，设置各种开关, 如缓存
// settingsElement(settings); 设置各种开关, 如缓存
private void settingsElement(Properties props) throws Exception {
configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));
configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));
configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
@SuppressWarnings("unchecked")
Class<? extends TypeHandler> typeHandler = (Class<? extends TypeHandler>)resolveClass(props.getProperty("defaultEnumTypeHandler"));
configuration.setDefaultEnumTypeHandler(typeHandler);
configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
configuration.setLogPrefix(props.getProperty("logPrefix"));
@SuppressWarnings("unchecked")
Class<? extends Log> logImpl = (Class<? extends Log>)resolveClass(props.getProperty("logImpl"));
configuration.setLogImpl(logImpl);
configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
}
environments 环境配置设置，根据指定环境，获取相应配置，加载数据源配置
// environmentsElement(root.evalNode("environments")); 环境配置
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
if (environment == null) {
// 默认为 development
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {
String id = child.getStringAttribute("id");
// 查找当前环境配置，指定加载
if (isSpecifiedEnvironment(id)) {
// 事务管理、数据源
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
DataSource dataSource = dsFactory.getDataSource();
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
// 环境配置包含， id, 事务管理, 数据源
public Environment build() {
return new Environment(this.id, this.transactionFactory, this.dataSource);
}
databaseIdProvider 解析，对多数据源，包含多 机器，或多类型数据库 mysql,sqlserver
// databaseIdProviderElement(root.evalNode("databaseIdProvider"));
private void databaseIdProviderElement(XNode context) throws Exception {
DatabaseIdProvider databaseIdProvider = null;
if (context != null) {
String type = context.getStringAttribute("type");
// awful patch to keep backward compatibility
if ("VENDOR".equals(type)) {
type = "DB_VENDOR";
}
Properties properties = context.getChildrenAsProperties();
databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
databaseIdProvider.setProperties(properties);
}
Environment environment = configuration.getEnvironment();
if (environment != null && databaseIdProvider != null) {
String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
configuration.setDatabaseId(databaseId);
}
}
自定义 typeHandler
// typeHandlerElement(root.evalNode("typeHandlers")); 自定义 typeHandler
private void typeHandlerElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String typeHandlerPackage = child.getStringAttribute("name");
typeHandlerRegistry.register(typeHandlerPackage);
} else {
String javaTypeName = child.getStringAttribute("javaType");
String jdbcTypeName = child.getStringAttribute("jdbcType");
String handlerTypeName = child.getStringAttribute("handler");
Class<?> javaTypeClass = resolveClass(javaTypeName);
JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
Class<?> typeHandlerClass = resolveClass(handlerTypeName);
if (javaTypeClass != null) {
if (jdbcType == null) {
typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
} else {
typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
}
} else {
typeHandlerRegistry.register(typeHandlerClass);
}
}
}
}
}
// org.apache.ibatis.type.TypeHandlerRegistry.register(), 以map保存映射
private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {
if (javaType != null) {
Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);
if (map == null || map == NULL_TYPE_HANDLER_MAP) {
map = new HashMap<>();
TYPE_HANDLER_MAP.put(javaType, map);
}
map.put(jdbcType, handler);
}
ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler);
}
mapper 解析，crud
// mapperElement(root.evalNode("mappers"));
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url == null && mapperClass != null) {
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
mapper解析细节
// org.apache.ibatis.builder.xml.XMLMapperBuilder.parse() mapper解析细节
public void parse() {
// 只解析一次 namespace
if (!configuration.isResourceLoaded(resource)) {
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();
} // 解析 resultMaps
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
cacheRefElement(context.evalNode("cache-ref"));
cacheElement(context.evalNode("cache"));
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
resultMapElements(context.evalNodes("/mapper/resultMap"));
sqlElement(context.evalNodes("/mapper/sql"));
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
}
} private void parsePendingResultMaps() {
Collection<ResultMapResolver> incompleteResultMaps = configuration.getIncompleteResultMaps();
synchronized (incompleteResultMaps) {
Iterator<ResultMapResolver> iter = incompleteResultMaps.iterator();
while (iter.hasNext()) {
try {
iter.next().resolve();
iter.remove();
} catch (IncompleteElementException e) {
// ResultMap is still missing a resource...
}
}
}
} private void parsePendingCacheRefs() {
Collection<CacheRefResolver> incompleteCacheRefs = configuration.getIncompleteCacheRefs();
synchronized (incompleteCacheRefs) {
Iterator<CacheRefResolver> iter = incompleteCacheRefs.iterator();
while (iter.hasNext()) {
try {
iter.next().resolveCacheRef();
iter.remove();
} catch (IncompleteElementException e) {
// Cache ref is still missing a resource...
}
}
}
} private void parsePendingStatements() {
Collection<XMLStatementBuilder> incompleteStatements = configuration.getIncompleteStatements();
synchronized (incompleteStatements) {
Iterator<XMLStatementBuilder> iter = incompleteStatements.iterator();
while (iter.hasNext()) {
try {
iter.next().parseStatementNode();
iter.remove();
} catch (IncompleteElementException e) {
// Statement is still missing a resource...
}
}
}
}
// 最后，返回一个 DefaultSqlSessionFactory, 载入配置项
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
// 会话创建好后，可以执行sql了
public void fullyPopulatedSubject() {
// 打开一个连接，使用完成后关闭
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
final Object subject = mapper.getSubject(1);
assertNotNull(subject);
}
}
2. 打开获得一个数据库会话连接
// org.apache.ibatis.session.defaults.SqlSession.openSession(); 打开一个数据库连接 @Override
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
// 运行环境获取
final Environment environment = configuration.getEnvironment();
// 事务管理工厂获取
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
// 创建新事务
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
// new Executor
final Executor executor = configuration.newExecutor(tx, execType);
// 最后返回 DefaultSqlSession 使用
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
// 关闭上下文监控
ErrorContext.instance().reset();
}
}
// org.apache.ibatis.session.Configuration.newExecutor()
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
// 根据不同请求类型创建不同的 executor
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
// 默认为 SIMPLE
executor = new SimpleExecutor(this, transaction);
}
if (cacheEnabled) {
// 创建缓存管理，将缓存请求委托给 executor 处理
executor = new CachingExecutor(executor);
}
// 处理plugin 请求
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
// org.apache.ibatis.executor.CachingExecutor
public CachingExecutor(Executor delegate) {
this.delegate = delegate;
delegate.setExecutorWrapper(this);
} // 最后将加载好的各种配置和实际处理，由 DefaultSqlSession 包装好后返回
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
3. 获取mapper,准备调用查询
// org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper()
@Override
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
} // org.apache.ibatis.binding.MapperRegistry.getMapper()
@SuppressWarnings("unchecked")
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
// 获取 MapperProxyFactory
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
// 创建 mapper 实例
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
} // org.apache.ibatis.binding.newInstance();
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
4. select, 查询数据
//mapper.getSubject(1); 查询数据
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
} else if (isDefaultMethod(method)) {
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
// 加载缓存包装方法
final MapperMethod mapperMethod = cachedMapperMethod(method);
// 执行查询
return mapperMethod.execute(sqlSession, args);
} private MapperMethod cachedMapperMethod(Method method) {
return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
} // org.apache.ibatis.binding.MapperMethod.execute(sqlSession, args); 针对不同类型语句，做不同调用
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession, args);
} else {
// 转换参数
Object param = method.convertArgsToSqlCommandParam(args);
// 执行单条查询
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional() &&
(result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException("Mapper method '" + command.getName()
+ " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
}
return result;
}
// org.apache.ibatis.reflection.ParamNameResolver.getNamedParams() 返回参数，如果是单个参数，直接返回参数值
// 如果是多个参数，则以 map 形式返回
public Object getNamedParams(Object[] args) {
final int paramCount = names.size();
if (args == null || paramCount == 0) {
return null;
} else if (!hasParamAnnotation && paramCount == 1) {
return args[names.firstKey()];
} else {
final Map<String, Object> param = new ParamMap<>();
int i = 0;
for (Map.Entry<Integer, String> entry : names.entrySet()) {
param.put(entry.getValue(), args[entry.getKey()]);
// add generic param names (param1, param2, ...)
final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1);
// ensure not to overwrite parameter named with @Param
if (!names.containsValue(genericParamName)) {
param.put(genericParamName, args[entry.getKey()]);
}
i++;
}
return param;
}
}
selectOne
// org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(command.getName(), param);
@Override
public <T> T selectOne(String statement, Object parameter) {
// Popular vote was to return null on 0 results and throw exception on too many.
// 查询单条记录时，默认也是先查询list,然后取第一条
List<T> list = this.<T>selectList(statement, parameter);
if (list.size() == 1) {
return list.get(0);
} else if (list.size() > 1) {
throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
} else {
return null;
}
} // 查询列表
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 先获取执行语句，此处 statement 为 id
MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
} // org.apache.ibatis.session.Configuration.getMappedStatement(id), 获取初始化解析出来的语句
public MappedStatement getMappedStatement(String id) {
return this.getMappedStatement(id, true);
}
public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
if (validateIncompleteStatements) {
buildAllStatements();
}
return mappedStatements.get(id);
}
包装执行 query
// executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
// org.apache.ibatis.executor.CachingExecutor.query()
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
// 获取sql
BoundSql boundSql = ms.getBoundSql(parameterObject);
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
} // org.apache.ibatis.mapping.MappedStatement.getBoundSql()
public BoundSql getBoundSql(Object parameterObject) {
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
// 字段映射
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {
boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
} // check for nested result maps in parameter mappings (issue #30)
for (ParameterMapping pm : boundSql.getParameterMappings()) {
String rmId = pm.getResultMapId();
if (rmId != null) {
ResultMap rm = configuration.getResultMap(rmId);
if (rm != null) {
hasNestedResultMaps |= rm.hasNestedResultMaps();
}
}
} return boundSql;
} // CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
// return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
// org.apache.ibatis.executor.CachingExecutor.query()
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
Cache cache = ms.getCache();
if (cache != null) {
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
前面的query是一个cache的包装类，其实际查询动作需要委托给excuttor，而我们主要关心 queryFromDb 逻辑！
// org.apache.ibatis.executor.SimpleExecutor.query() / BaseExecutor
@SuppressWarnings("unchecked")
@Override
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
if (closed) {
throw new ExecutorException("Executor was closed.");
}
// 缓存刷新
if (queryStack == 0 && ms.isFlushCacheRequired()) {
clearLocalCache();
}
List<E> list;
try {
queryStack++;
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// 没有缓存，走db
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
} // BaseExecutor
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
// 缓存占位符
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
// 防止异常情况，保证将占位缓存删除
localCache.removeObject(key);
}
// 操作完成后，重新放入缓存
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
执行 doQuery，主要是获取完整的 statement，使handler有据可查！
@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
// 获取全局配置
Configuration configuration = ms.getConfiguration();
// 获取statement, 处理 JDBC 接口
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.<E>query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
// org.apache.ibatis.session.Configuration.newStatementHandler(), 兼顾 plugins,
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
db查询
// 为不同处理类型，建立不同的 handler
public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { switch (ms.getStatementType()) {
case STATEMENT:
delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case PREPARED:
delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case CALLABLE:
delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
default:
throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
} } //stmt = prepareStatement(handler, ms.getStatementLog());
// org.apache.ibatis.executor.SimpleExecutor.prepareStatement(), 获取 statement, JDBC
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
Connection connection = getConnection(statementLog);
// sql录入
stmt = handler.prepare(connection, transaction.getTimeout());
// 参数绑定
handler.parameterize(stmt);
return stmt;
} // BaseExecutor
protected Connection getConnection(Log statementLog) throws SQLException {
Connection connection = transaction.getConnection();
if (statementLog.isDebugEnabled()) {
return ConnectionLogger.newInstance(connection, statementLog, queryStack);
} else {
return connection;
}
} // org.apache.ibatis.transaction.jdbc.JdbcTransaction.getConnection()
@Override
public Connection getConnection() throws SQLException {
if (connection == null) {
// 为空时新建 connection
openConnection();
}
return connection;
} protected void openConnection() throws SQLException {
if (log.isDebugEnabled()) {
log.debug("Opening JDBC Connection");
}
connection = dataSource.getConnection();
if (level != null) {
connection.setTransactionIsolation(level.getLevel());
}
setDesiredAutoCommit(autoCommit);
} // org.apache.ibatis.datasource.unpooled.getConnection()
@Override
public Connection getConnection() throws SQLException {
return doGetConnection(username, password);
} private Connection doGetConnection(String username, String password) throws SQLException {
Properties props = new Properties();
if (driverProperties != null) {
props.putAll(driverProperties);
}
if (username != null) {
props.setProperty("user", username);
}
if (password != null) {
props.setProperty("password", password);
}
return doGetConnection(props);
} private Connection doGetConnection(Properties properties) throws SQLException {
// 如果没有初始化驱动，初始化
initializeDriver();
//
Connection connection = DriverManager.getConnection(url, properties);
configureConnection(connection);
return connection;
} private synchronized void initializeDriver() throws SQLException {
if (!registeredDrivers.containsKey(driver)) {
Class<?> driverType;
try {
// 加载驱动
if (driverClassLoader != null) {
driverType = Class.forName(driver, true, driverClassLoader);
} else {
driverType = Resources.classForName(driver);
}
// DriverManager requires the driver to be loaded via the system ClassLoader.
// http://www.kfu.com/~nsayer/Java/dyn-jdbc.html
Driver driverInstance = (Driver)driverType.newInstance();
DriverManager.registerDriver(new DriverProxy(driverInstance));
registeredDrivers.put(driver, driverInstance);
} catch (Exception e) {
throw new SQLException("Error setting driver on UnpooledDataSource. Cause: " + e);
}
}
} private void configureConnection(Connection conn) throws SQLException {
if (autoCommit != null && autoCommit != conn.getAutoCommit()) {
conn.setAutoCommit(autoCommit);
}
if (defaultTransactionIsolationLevel != null) {
conn.setTransactionIsolation(defaultTransactionIsolationLevel);
}
} // stmt = handler.prepare(connection, transaction.getTimeout()); 组装sql
// org.apache.ibatis.executor.statement.RoutingStatementHandler.prepare()
@Override
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
return delegate.prepare(connection, transactionTimeout);
} // org.apache.ibatis.executor.statement.PreparedStatementHandler.
@Override
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
ErrorContext.instance().sql(boundSql.getSql());
Statement statement = null;
try {
// select * from tab where id = ?
statement = instantiateStatement(connection);
// 设置超时
setStatementTimeout(statement, transactionTimeout);
// 设置查询大小，默认不限制
setFetchSize(statement);
return statement;
} catch (SQLException e) {
closeStatement(statement);
throw e;
} catch (Exception e) {
closeStatement(statement);
throw new ExecutorException("Error preparing statement. Cause: " + e, e);
}
} // 调用jdbc connection.prepareStatement(sql), 初始化语句
@Override
protected Statement instantiateStatement(Connection connection) throws SQLException {
String sql = boundSql.getSql();
if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
String[] keyColumnNames = mappedStatement.getKeyColumns();
if (keyColumnNames == null) {
return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
} else {
return connection.prepareStatement(sql, keyColumnNames);
}
} else if (mappedStatement.getResultSetType() == ResultSetType.DEFAULT) {
return connection.prepareStatement(sql);
} else {
return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
}
} // PreparedStatementHandler handler.parameterize(stmt);
@Override
public void parameterize(Statement statement) throws SQLException {
parameterHandler.setParameters((PreparedStatement) statement);
} // org.apache.ibatis.scripting.defaults.DefaultParameterHandler.setParameters()
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
MetaObject metaObject = configuration.newMetaObject(parameterObject);
value = metaObject.getValue(propertyName);
}
// TypeHandler 处理参数类型
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
} // return handler.<E>query(stmt, resultHandler);
// org.apache.ibatis.executor.statement.RoutingStatementHandler.query()
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
return delegate.<E>query(statement, resultHandler);
} // PreparedStatementHandler.query()
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
// 调用驱动程序执行 execute
ps.execute();
// 处理结果集映射
return resultSetHandler.<E> handleResultSets(ps);
} // org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(), 处理结果集映射
@Override
public List<Object> handleResultSets(Statement stmt) throws SQLException {
ErrorContext.instance().activity("handling results").object(mappedStatement.getId()); final List<Object> multipleResults = new ArrayList<>(); int resultSetCount = 0;
// 获取第一个结果集（开始偏移的地方）
ResultSetWrapper rsw = getFirstResultSet(stmt); List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
ResultMap resultMap = resultMaps.get(resultSetCount);
handleResultSet(rsw, resultMap, multipleResults, null);
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
} String[] resultSets = mappedStatement.getResultSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
handleResultSet(rsw, resultMap, null, parentMapping);
}
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
} return collapseSingleResultList(multipleResults);
} // org.apache.ibatis.executor.resultset.ResultSetWrapper, 根据第一行返回数据集，初始化字段名及字段类型
public ResultSetWrapper(ResultSet rs, Configuration configuration) throws SQLException {
super();
this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
this.resultSet = rs;
final ResultSetMetaData metaData = rs.getMetaData();
final int columnCount = metaData.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
columnNames.add(configuration.isUseColumnLabel() ? metaData.getColumnLabel(i) : metaData.getColumnName(i));
// java.sql.Types, 处理返回的类型为具体的java类型映射到 org.apache.ibatis.type.JdbcType
jdbcTypes.add(JdbcType.forCode(metaData.getColumnType(i)));
// java 类型全名
classNames.add(metaData.getColumnClassName(i));
}
}
数据库结果映射到javabean
// DefaultResultSetHandler.handleResultSet() 处理单条记录映射关系
private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
try {
if (parentMapping != null) {
handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
} else {
if (resultHandler == null) {
DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
multipleResults.add(defaultResultHandler.getResultList());
} else {
handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
}
}
} finally {
// issue #228 (close resultsets)
closeResultSet(rsw.getResultSet());
}
}
// handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
public void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
if (resultMap.hasNestedResultMaps()) {
// 嵌套数据的映射
ensureNoRowBounds();
checkResultHandler();
handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
} else {
// 简单数据映射
handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
}
}
// 简单数据映射
private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
throws SQLException {
DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
ResultSet resultSet = rsw.getResultSet();
// 跳过行偏移，难道不是在数据sql中添加 limit 进行数据筛选的？
skipRows(resultSet, rowBounds);
while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
// 1. Discriminated 鉴别器
ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
//
Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
}
}
// 检测超过 limit 后，不再继续获取结果
private boolean shouldProcessMoreRows(ResultContext<?> context, RowBounds rowBounds) {
return !context.isStopped() && context.getResultCount() < rowBounds.getLimit();
}
// Discriminated
public ResultMap resolveDiscriminatedResultMap(ResultSet rs, ResultMap resultMap, String columnPrefix) throws SQLException {
Set<String> pastDiscriminators = new HashSet<>();
Discriminator discriminator = resultMap.getDiscriminator();
while (discriminator != null) {
final Object value = getDiscriminatorValue(rs, discriminator, columnPrefix);
final String discriminatedMapId = discriminator.getMapIdFor(String.valueOf(value));
if (configuration.hasResultMap(discriminatedMapId)) {
resultMap = configuration.getResultMap(discriminatedMapId);
Discriminator lastDiscriminator = discriminator;
discriminator = resultMap.getDiscriminator();
if (discriminator == lastDiscriminator || !pastDiscriminators.add(discriminatedMapId)) {
break;
}
} else {
break;
}
}
return resultMap;
} // 从结果set中获取值
private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
final ResultLoaderMap lazyLoader = new ResultLoaderMap();
Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
final MetaObject metaObject = configuration.newMetaObject(rowValue);
boolean foundValues = this.useConstructorMappings;
if (shouldApplyAutomaticMappings(resultMap, false)) {
foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
}
foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
foundValues = lazyLoader.size() > 0 || foundValues;
rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
}
return rowValue;
} // DefaultResultSetHandler
private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix)
throws SQLException {
final Class<?> resultType = resultMap.getType();
final MetaClass metaType = MetaClass.forClass(resultType, reflectorFactory);
final List<ResultMapping> constructorMappings = resultMap.getConstructorResultMappings();
if (hasTypeHandlerForResultObject(rsw, resultType)) {
return createPrimitiveResultObject(rsw, resultMap, columnPrefix);
} else if (!constructorMappings.isEmpty()) {
return createParameterizedResultObject(rsw, resultType, constructorMappings, constructorArgTypes, constructorArgs, columnPrefix);
} else if (resultType.isInterface() || metaType.hasDefaultConstructor()) {
return objectFactory.create(resultType);
} else if (shouldApplyAutomaticMappings(resultMap, false)) {
return createByConstructorSignature(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix);
}
throw new ExecutorException("Do not know how to create an instance of " + resultType);
} // 构造器注入方式
private Object createByConstructorSignature(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs,
String columnPrefix) throws SQLException {
final Constructor<?>[] constructors = resultType.getDeclaredConstructors();
final Constructor<?> defaultConstructor = findDefaultConstructor(constructors);
if (defaultConstructor != null) {
return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix, defaultConstructor);
} else {
for (Constructor<?> constructor : constructors) {
if (allowedConstructorUsingTypeHandlers(constructor, rsw.getJdbcTypes())) {
return createUsingConstructor(rsw, resultType, constructorArgTypes, constructorArgs, columnPrefix, constructor);
}
}
}
throw new ExecutorException("No constructor found in " + resultType.getName() + " matching " + rsw.getClassNames());
} private Object createUsingConstructor(ResultSetWrapper rsw, Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix, Constructor<?> constructor) throws SQLException {
boolean foundValues = false;
for (int i = 0; i < constructor.getParameterTypes().length; i++) {
Class<?> parameterType = constructor.getParameterTypes()[i];
String columnName = rsw.getColumnNames().get(i);
TypeHandler<?> typeHandler = rsw.getTypeHandler(parameterType, columnName);
Object value = typeHandler.getResult(rsw.getResultSet(), prependPrefix(columnName, columnPrefix));
constructorArgTypes.add(parameterType);
constructorArgs.add(value);
foundValues = value != null || foundValues;
}
// 调用构造方法注入值
return foundValues ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;
}
// org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(), 调用构造器返回 bean 实例
@SuppressWarnings("unchecked")
@Override
public <T> T create(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
Class<?> classToCreate = resolveInterface(type);
// we know types are assignable
return (T) instantiateClass(classToCreate, constructorArgTypes, constructorArgs);
} private <T> T instantiateClass(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
try {
Constructor<T> constructor;
if (constructorArgTypes == null || constructorArgs == null) {
constructor = type.getDeclaredConstructor();
try {
return constructor.newInstance();
} catch (IllegalAccessException e) {
if (Reflector.canControlMemberAccessible()) {
constructor.setAccessible(true);
return constructor.newInstance();
} else {
throw e;
}
}
}
constructor = type.getDeclaredConstructor(constructorArgTypes.toArray(new Class[constructorArgTypes.size()]));
try {
return constructor.newInstance(constructorArgs.toArray(new Object[constructorArgs.size()]));
} catch (IllegalAccessException e) {
if (Reflector.canControlMemberAccessible()) {
constructor.setAccessible(true);
return constructor.newInstance(constructorArgs.toArray(new Object[constructorArgs.size()]));
} else {
throw e;
}
}
} catch (Exception e) {
StringBuilder argTypes = new StringBuilder();
if (constructorArgTypes != null && !constructorArgTypes.isEmpty()) {
for (Class<?> argType : constructorArgTypes) {
argTypes.append(argType.getSimpleName());
argTypes.append(",");
}
argTypes.deleteCharAt(argTypes.length() - 1); // remove trailing ,
}
StringBuilder argValues = new StringBuilder();
if (constructorArgs != null && !constructorArgs.isEmpty()) {
for (Object argValue : constructorArgs) {
argValues.append(String.valueOf(argValue));
argValues.append(",");
}
argValues.deleteCharAt(argValues.length() - 1); // remove trailing ,
}
throw new ReflectionException("Error instantiating " + type + " with invalid types (" + argTypes + ") or values (" + argValues + "). Cause: " + e, e);
}
}
数据集获取
// 保存结果
private void storeObject(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue, ResultMapping parentMapping, ResultSet rs) throws SQLException {
if (parentMapping != null) {
linkToParents(rs, parentMapping, rowValue);
} else {
callResultHandler(resultHandler, resultContext, rowValue);
}
} @SuppressWarnings("unchecked" /* because ResultHandler<?> is always ResultHandler<Object>*/)
private void callResultHandler(ResultHandler<?> resultHandler, DefaultResultContext<Object> resultContext, Object rowValue) {
resultContext.nextResultObject(rowValue);
((ResultHandler<Object>) resultHandler).handleResult(resultContext);
}
//
private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
throws SQLException {
final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
boolean foundValues = false;
final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
for (ResultMapping propertyMapping : propertyMappings) {
String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
if (propertyMapping.getNestedResultMapId() != null) {
// the user added a column attribute to a nested result map, ignore it
column = null;
}
if (propertyMapping.isCompositeResult()
|| (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))
|| propertyMapping.getResultSet() != null) {
Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
// issue #541 make property optional
final String property = propertyMapping.getProperty();
if (property == null) {
continue;
} else if (value == DEFERED) {
foundValues = true;
continue;
}
if (value != null) {
foundValues = true;
}
if (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive())) {
// gcode issue #377, call setter on nulls (value is not 'found')
metaObject.setValue(property, value);
}
}
}
return foundValues;
} // collapseSingleResultList(multipleResults); 转换多级 list 为1级list
@SuppressWarnings("unchecked")
private List<Object> collapseSingleResultList(List<Object> multipleResults) {
return multipleResults.size() == 1 ? (List<Object>) multipleResults.get(0) : multipleResults;
}
至此，一条select 语句搞定！
主要经历几个阶段：
1. 加载配置
2. 创建sqlSessionFactory
3. 获取sqlSession
4. jdbc连接
5. 获取mapper
6. 查询参数绑定
7. 获取db结果
8. 处理返回集字段映射
9. 缓存结果
10. 返回结果