Shulou(Shulou.com)06/02 Report--

这篇文章将为大家详细讲解有关Mybatis中Executor的作用是什么，文章内容质量较高，因此小编分享给大家做个参考，希望大家阅读完这篇文章后对相关知识有一定的了解。

1.BatchExecutor

BatchExecutor与其它的区别是update方法中，使用的是StatementHandler的batch方法，如下List-1

List-1

public class BatchExecutor extends BaseExecutor { ... @Override public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException { final Configuration configuration = ms.getConfiguration(); final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null); final BoundSql boundSql = handler.getBoundSql(); final String sql = boundSql.getSql(); final Statement stmt; if (sql.equals(currentSql) && ms.equals(currentStatement)) { int last = statementList.size() - 1; stmt = statementList.get(last); applyTransactionTimeout(stmt); handler.parameterize(stmt);//fix Issues 322 BatchResult batchResult = batchResultList.get(last); batchResult.addParameterObject(parameterObject); } else { Connection connection = getConnection(ms.getStatementLog()); stmt = handler.prepare(connection, transaction.getTimeout()); handler.parameterize(stmt); //fix Issues 322 currentSql = sql; currentStatement = ms; statementList.add(stmt); batchResultList.add(new BatchResult(ms, sql, parameterObject)); } // handler.parameterize(stmt); handler.batch(stmt); return BATCH_UPDATE_RETURN_VALUE; } ...2.ReuseExecutor

ReuseExecutor与其它executor的区别是重用jdbc的Statement，有个map属性，ReuseExecutor的doUpdate、doQuery中，调用prepareStatement时，如下List-2，会根据sql来判断是否已经存在对应的Statement，如果map中已经有了则直接使用，如果不存在，则通过PrepareStatementHandler.prepare方法获取对Statement，之后放入到map中。

List-2

public class ReuseExecutor extends BaseExecutor { ... private final Map statementMap = new HashMap(); ... private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Statement stmt; BoundSql boundSql = handler.getBoundSql(); String sql = boundSql.getSql(); if (hasStatementFor(sql)) { stmt = getStatement(sql); applyTransactionTimeout(stmt); } else { Connection connection = getConnection(statementLog); stmt = handler.prepare(connection, transaction.getTimeout()); putStatement(sql, stmt); } handler.parameterize(stmt); return stmt; } private boolean hasStatementFor(String sql) { try { return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed(); } catch (SQLException e) { return false; } } private Statement getStatement(String s) { return statementMap.get(s); } private void putStatement(String sql, Statement stmt) { statementMap.put(sql, stmt); }3.SimpleExecutor

SimpleExecutor与ReuseExecutor和BatchExecutor不同，即没有重用Statement，在update时也没有使用StatementHandler的batch方法，而是用了update方法。

4.CachingExecutor

CachingExecutor有点特殊，使用了Delete模式，此外用到了Cache，如下List-3

List-3

public class CachingExecutor implements Executor { private final Executor delegate; private final TransactionalCacheManager tcm = new TransactionalCacheManager(); public CachingExecutor(Executor delegate) { this.delegate = delegate; delegate.setExecutorWrapper(this); }...

来看TransactionalCacheManager，如下List-4，通过Cache这个key，得到TransactionalCache，当调用getObject方法时，间接调用TransactionalCache.getObject.

List-4

public class TransactionalCacheManager { private final Map transactionalCaches = new HashMap(); public void clear(Cache cache) { getTransactionalCache(cache).clear(); } public Object getObject(Cache cache, CacheKey key) { return getTransactionalCache(cache).getObject(key); } public void putObject(Cache cache, CacheKey key, Object value) { getTransactionalCache(cache).putObject(key, value); } public void commit() { for (TransactionalCache txCache : transactionalCaches.values()) { txCache.commit(); } } public void rollback() { for (TransactionalCache txCache : transactionalCaches.values()) { txCache.rollback(); } }

List-5

public class TransactionalCache implements Cache { private final Cache delegate; private boolean clearOnCommit; private final Map entriesToAddOnCommit; private final Set entriesMissedInCache; public TransactionalCache(Cache delegate) { this.delegate = delegate; this.clearOnCommit = false; this.entriesToAddOnCommit = new HashMap(); this.entriesMissedInCache = new HashSet(); } @Override public Object getObject(Object key) { // issue #116 Object object = delegate.getObject(key); if (object == null) { entriesMissedInCache.add(key); } // issue #146 if (clearOnCommit) { return null; } else { return object; } }

List-5中，getObject方法中，从委托的cache中getObject如果不是null则返回，不为null则还需要更新统计。

所以mybatis中可以使用二级缓存就是通过这个Cache来实现的。

在没有特殊设置的情况下，mybatis中，如下List-6，默认使用的executor是SimpleExecutor，StatementHandler是RoutingStatementHandler，内部委托给PrepareStatementHandler。

List-6

select * from person where username=#{username};

如下List-7，没有参数设置，默认情况下使用的还是SimpleExecutor、RoutingStatementHandler--内部委托给PrepareStatementHandler.

List-7

select * from person关于Mybatis中Executor的作用是什么就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。

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