mybatis 细粒度控制二级缓存

时间:2022-02-28 07:30:46

  本文要解决的问题:细粒度控制mybatis的二级缓存。mybatis的二级缓存的问题:当更新SQL执行时只清除当前SQL所在命名空间(namespace)的缓存。如果存在2个命名空间namespaceA和namespaceB,当namespaceA下执行更新操作时,namespaceB的缓存并不会清除。正常的情况下,这种策略是不会有问题。但是,如果存在关联查询时就有可能出现问题了,例如namespaceA关联namespaceB,当namespaceB执行更新时清除namespaceB的缓存,这是查询namespaceA时,会导致查询出来的结果是缓存的,即数据不是最新的。步骤如下:

    1. 开启mybatis二级缓存

  1. <settings>
    <setting name="cacheEnabled" value="true" />
    </settings>

    2. 加入SQL分析的jar依赖

    <dependency>
    <groupId>com.github.jsqlparser</groupId>
    <artifactId>jsqlparser</artifactId>
    <version>0.9.4</version>
    </dependency>

    3. 复制如下拦截器代码

    package com.xyz.core.inctercepter;
    
    import java.util.Collection;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import java.util.Properties; import org.apache.ibatis.executor.Executor;
    import org.apache.ibatis.mapping.BoundSql;
    import org.apache.ibatis.mapping.MappedStatement;
    import org.apache.ibatis.plugin.Interceptor;
    import org.apache.ibatis.plugin.Intercepts;
    import org.apache.ibatis.plugin.Invocation;
    import org.apache.ibatis.plugin.Plugin;
    import org.apache.ibatis.plugin.Signature;
    import org.apache.ibatis.session.Configuration;
    import org.apache.ibatis.session.ResultHandler;
    import org.apache.ibatis.session.RowBounds;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory; import net.sf.jsqlparser.JSQLParserException;
    import net.sf.jsqlparser.parser.CCJSqlParserUtil;
    import net.sf.jsqlparser.statement.Statement;
    import net.sf.jsqlparser.statement.delete.Delete;
    import net.sf.jsqlparser.statement.insert.Insert;
    import net.sf.jsqlparser.statement.select.Select;
    import net.sf.jsqlparser.statement.update.Update;
    import net.sf.jsqlparser.util.TablesNamesFinder; /**
    * 缓存控制拦截器
    *
    * @author lee
    * @since 2016年3月17日
    */
    @Intercepts({
    @Signature(method = "query", type = Executor.class, args = { MappedStatement.class, Object.class,
    RowBounds.class, ResultHandler.class }),
    @Signature(method = "update", type = Executor.class, args = { MappedStatement.class, Object.class }) })
    public class CachingInterceptor implements Interceptor {
    private final static Logger logger = LoggerFactory.getLogger(CachingInterceptor.class);
    /**
    * 表名关联的命名空间<br/>
    * 一个table下关联的namespace
    */
    private final static Map<String, Map<String, String>> tableLinks = new HashMap<String, Map<String, String>>(); /**
    * 记录已经解析过的SQL,确保一条SQL只被解析一次,提高效率
    */
    private final static Map<String, String> dealedMap = new HashMap<String, String>(); public Object intercept(Invocation invocation) throws Throwable {
    Object[] args = invocation.getArgs();
    MappedStatement ms = (MappedStatement) args[0];
    BoundSql boundSql = ms.getBoundSql(args[1]);
    if (!ms.getConfiguration().isCacheEnabled() || ms.getCache() == null)
    return invocation.proceed();
    if (dealedMap.containsKey(ms.getId()) && dealedMap.get(ms.getId()).equals(boundSql.getSql())) {
    return invocation.proceed();
    }
    dealedMap.put(ms.getId(), boundSql.getSql()); final String operate = invocation.getMethod().getName();
    final List<String> tableNames = getTableList(boundSql.getSql());
    final String namespace = ms.getCache().getId();
    logger.debug("当前操作SQL中包含的namespace:" + namespace);
    if ("query".equals(operate)) {
    deal(namespace, tableNames);
    } else {
    Configuration configuration = ms.getConfiguration();
    clearCache(tableNames, configuration.getMappedStatements());
    } return invocation.proceed();
    } public Object plugin(Object target) {
    return Plugin.wrap(target, this);
    } public void setProperties(Properties properties) {
    } /**
    * 一个namespace包含多个SQL<br/>
    * 一条SQL语句包含多个table
    *
    * @param namespace
    * @param tableNames
    */
    private void deal(final String namespace, final List<String> tableNames) {
    if (tableNames == null || tableNames.size() == 0)
    return; for (String tableName : tableNames) {
    Map<String, String> namespaces = tableLinks.get(tableName);
    if (namespaces == null) {
    namespaces = new HashMap<String, String>();
    namespaces.put(namespace, namespace);
    tableLinks.put(tableName, namespaces);
    } else if (!namespaces.containsKey(namespace)) {
    namespaces.put(namespace, namespace);
    }
    }
    } /**
    * 清除缓存
    *
    * @param mappedStatments
    */
    @SuppressWarnings("rawtypes")
    private void clearCache(List<String> tableNames, Collection mappedStatments) {
    if (tableNames == null || tableNames.isEmpty())
    return;
    for (String tableName : tableNames) {
    Map<String, String> namespaces = tableLinks.get(tableName);
    if (namespaces == null)
    continue;
    for (String namespaceNeedClearKey : namespaces.keySet()) {
    for (Object o : mappedStatments) {
    if (o instanceof MappedStatement) {
    MappedStatement sta = ((MappedStatement) o);
    final String namespace = sta.getCache().getId();
    if (namespaceNeedClearKey.equals(namespace)) {
    logger.debug("命名空间[{}]的缓存被清除", namespace);
    sta.getCache().clear();
    break;
    }
    }
    }
    }
    }
    } /**
    * 解析SQL中包含的表名
    *
    * @param sql
    * @return
    */
    public List<String> getTableList(final String sql) {
    try {
    Statement statement = CCJSqlParserUtil.parse(sql);
    TablesNamesFinder tablesNamesFinder = new TablesNamesFinder();
    List<String> tableList = null;
    if (statement instanceof Select) {
    Select selectStatement = (Select) statement;
    tableList = tablesNamesFinder.getTableList(selectStatement);
    } else if (statement instanceof Update) {
    Update updateStatement = (Update) statement;
    tableList = tablesNamesFinder.getTableList(updateStatement);
    } else if (statement instanceof Insert) {
    Insert insertStatement = (Insert) statement;
    tableList = tablesNamesFinder.getTableList(insertStatement);
    } else if (statement instanceof Delete) {
    Delete deleteStatement = (Delete) statement;
    tableList = tablesNamesFinder.getTableList(deleteStatement);
    }
    logger.debug("SQL:{}中包含的表名:" + tableList, sql);
    return tableList;
    } catch (JSQLParserException e) {
    logger.error("解析sql异常:" + sql, e);
    }
    return null;
    }
    }

    4. 配置mybatis拦截器

        <plugins>
    <plugin interceptor="com.xyz.core.inctercepter.CachingInterceptor" />
    </plugins>