为了方便修改BUG,我在github上创建了一个仓库,地址:https://github.com/hupanfeng/hdd。欢迎大家在留言里提交问题,我会尽快修复,并将修复的代码提交至github上。
在前面的文章里,我开发了两个插件:根据注解实现的sql自动生成插件和分页插件。这两个插件在没有开启cache的情况下可以很好的使用,但开启cache后却出现了一些问题,为了解决这些问题,我编写了拦截cache的插件,通过这个拦截器修正了这些问题。
问题
什么问题
最容易出现的问题是开启cache后,分页查询时无论查询哪一页都返回第一页的数据。另外,使用sql自动生成插件生成get方法的sql时,传入的参数不起作用,无论传入的参数是多少,都返回第一个参数的查询结果。
为什么出现这些问题
在之前讲解Mybatis的执行流程的时候提到,在开启cache的前提下,Mybatis的executor会先从缓存里读取数据,读取不到才去数据库查询。问题就出在这里,sql自动生成插件和分页插件执行的时机是在statementhandler里,而statementhandler是在executor之后执行的,无论sql自动生成插件和分页插件都是通过改写sql来实现的,executor在生成读取cache的key(key由sql以及对应的参数值构成)时使用都是原始的sql,这样当然就出问题了。
解决问题
找到问题的原因后,解决起来就方便了。只要通过拦截器改写executor里生成key的方法,在生成可以时使用自动生成的sql(对应sql自动生成插件)或加入分页信息(对应分页插件)就可以了。
拦截器签名
[java] view plain copy- @Intercepts({@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
- public class CacheInterceptor implements Interceptor {
- ...
- }
从签名里可以看出,要拦截的目标类型是Executor(注意:type只能配置成接口类型),拦截的方法是名称为query的方法。
intercept的实现
[java] view plain copy- public Object intercept(Invocation invocation) throws Throwable {
- Executor executorProxy = (Executor) invocation.getTarget();
- MetaObject metaExecutor = MetaObject.forObject(executorProxy, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);
- // 分离代理对象链
- while (metaExecutor.hasGetter("h")) {
- Object object = metaExecutor.getValue("h");
- metaExecutor = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);
- }
- // 分离最后一个代理对象的目标类
- while (metaExecutor.hasGetter("target")) {
- Object object = metaExecutor.getValue("target");
- metaExecutor = MetaObject.forObject(object, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);
- }
- Object[] args = invocation.getArgs();
- return this.query(metaExecutor, args);
- }
- public <E> List<E> query(MetaObject metaExecutor, Object[] args) throws SQLException {
- MappedStatement ms = (MappedStatement) args[0];
- Object parameterObject = args[1];
- RowBounds rowBounds = (RowBounds) args[2];
- ResultHandler resultHandler = (ResultHandler) args[3];
- BoundSql boundSql = ms.getBoundSql(parameterObject);
- // 改写key的生成
- CacheKey cacheKey = createCacheKey(ms, parameterObject, rowBounds, boundSql);
- Executor executor = (Executor) metaExecutor.getOriginalObject();
- return executor.query(ms, parameterObject, rowBounds, resultHandler, cacheKey, boundSql);
- }
- private CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {
- Configuration configuration = ms.getConfiguration();
- pageSqlId = configuration.getVariables().getProperty("pageSqlId");
- if (null == pageSqlId || "".equals(pageSqlId)) {
- logger.warn("Property pageSqlId is not setted,use default '.*Page$' ");
- pageSqlId = defaultPageSqlId;
- }
- CacheKey cacheKey = new CacheKey();
- cacheKey.update(ms.getId());
- cacheKey.update(rowBounds.getOffset());
- cacheKey.update(rowBounds.getLimit());
- List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
- // 解决自动生成SQL,SQL语句为空导致key生成错误的bug
- if (null == boundSql.getSql() || "".equals(boundSql.getSql())) {
- String id = ms.getId();
- id = id.substring(id.lastIndexOf(".") + 1);
- String newSql = null;
- try {
- if ("select".equals(id)) {
- newSql = SqlBuilder.buildSelectSql(parameterObject);
- }
- SqlSource sqlSource = buildSqlSource(configuration, newSql, parameterObject.getClass());
- parameterMappings = sqlSource.getBoundSql(parameterObject).getParameterMappings();
- cacheKey.update(newSql);
- } catch (Exception e) {
- logger.error("Update cacheKey error.", e);
- }
- } else {
- cacheKey.update(boundSql.getSql());
- }
- MetaObject metaObject = MetaObject.forObject(parameterObject, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY);
- if (parameterMappings.size() > 0 && parameterObject != null) {
- TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();
- if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
- cacheKey.update(parameterObject);
- } else {
- for (ParameterMapping parameterMapping : parameterMappings) {
- String propertyName = parameterMapping.getProperty();
- if (metaObject.hasGetter(propertyName)) {
- cacheKey.update(metaObject.getValue(propertyName));
- } else if (boundSql.hasAdditionalParameter(propertyName)) {
- cacheKey.update(boundSql.getAdditionalParameter(propertyName));
- }
- }
- }
- }
- // 当需要分页查询时,将page参数里的当前页和每页数加到cachekey里
- if (ms.getId().matches(pageSqlId) && metaObject.hasGetter("page")) {
- PageParameter page = (PageParameter) metaObject.getValue("page");
- if (null != page) {
- cacheKey.update(page.getCurrentPage());
- cacheKey.update(page.getPageSize());
- }
- }
- return cacheKey;
- }
plugin的实现
[java] view plain copy- public Object plugin(Object target) {
- // 当目标类是CachingExecutor类型时,才包装目标类,否者直接返回目标本身,减少目标被代理的
- // 次数
- if (target instanceof CachingExecutor) {
- return Plugin.wrap(target, this);
- } else {
- return target;
- }
- }