Spring的JdbcTemplate自动关闭连接

逃离我推掉我的手 2022-05-22 10:58 1166阅读 0赞

来源：https://blog.csdn.net/partner4java/article/details/7012196

JdbcTemplate类使用DataSource得到一个数据库连接。然后，他调用StatementCreator实例创建要执行的语句。下一步，他调用StatementCallBack完成。  
一旦StatementCallBack返回结果，JdbcTemplate类完成所有必要清理工作关闭连接。如果StatementCreator或StatementCallBack抛出异常，JdbcTemplate类会捕获他们，并转换为Spring数据访问异常。

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看一个JdbcTemplate里面的比较核心的一个方法：

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1.  //-------------------------------------------------------------------------  
2.  // Methods dealing with prepared statements  
3.  //-------------------------------------------------------------------------  
4.    
5.  **public** Object execute(PreparedStatementCreator psc, PreparedStatementCallback action)  
6.          **throws** DataAccessException \{  
7.    
8.      Assert.notNull(psc, "PreparedStatementCreator must not be null");  
9.      Assert.notNull(action, "Callback object must not be null");  
10.     **if** (logger.isDebugEnabled()) \{  
11.         String sql = getSql(psc);  
12.         logger.debug("Executing prepared SQL statement" + (sql != **null** ? " \[" + sql + "\]" : ""));  
13.     \}  
14.   
15.     Connection con = DataSourceUtils.getConnection(getDataSource());  
16.     PreparedStatement ps = **null**;  
17.     **try** \{  
18.         Connection conToUse = con;  
19.         **if** (**this**.nativeJdbcExtractor != **null** &&  
20.                 **this**.nativeJdbcExtractor.isNativeConnectionNecessaryForNativePreparedStatements()) \{  
21.             conToUse = **this**.nativeJdbcExtractor.getNativeConnection(con);  
22.         \}  
23.         ps = psc.createPreparedStatement(conToUse);  
24.         applyStatementSettings(ps);  
25.         PreparedStatement psToUse = ps;  
26.         **if** (**this**.nativeJdbcExtractor != **null**) \{  
27.             psToUse = **this**.nativeJdbcExtractor.getNativePreparedStatement(ps);  
28.         \}  
29.         Object result = action.doInPreparedStatement(psToUse);  
30.         handleWarnings(ps);  
31.         **return** result;  
32.     \}  
33.     **catch** (SQLException ex) \{  
34.         // Release Connection early, to avoid potential connection pool deadlock  
35.         // in the case when the exception translator hasn't been initialized yet.  
36.         **if** (psc **instanceof** ParameterDisposer) \{  
37.             ((ParameterDisposer) psc).cleanupParameters();  
38.         \}  
39.         String sql = getSql(psc);  
40.         psc = **null**;  
41.         JdbcUtils.closeStatement(ps);  
42.         ps = **null**;  
43.         DataSourceUtils.releaseConnection(con, getDataSource());  
44.         con = **null**;  
45.         **throw** getExceptionTranslator().translate("PreparedStatementCallback", sql, ex);  
46.     \}  
47.     **finally** \{  
48.         **if** (psc **instanceof** ParameterDisposer) \{  
49.             ((ParameterDisposer) psc).cleanupParameters();  
50.         \}  
51.         JdbcUtils.closeStatement(ps);  
52.         DataSourceUtils.releaseConnection(con, getDataSource());  
53.     \}  
54. \}

显然，我们在finally里面看到了关闭调用，在看看这个关闭调用方法内部：

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1.  /\*\* 
2.  \* Close the given Connection, obtained from the given DataSource, 
3.  \* if it is not managed externally (that is, not bound to the thread). 
4.  \* @param con the Connection to close if necessary 
5.  \* (if this is <code>null</code>, the call will be ignored) 
6.  \* @param dataSource the DataSource that the Connection was obtained from 
7.  \* (may be <code>null</code>) 
8.  \* @see \#getConnection 
9.  \*/  
10. **public** **static** **void** releaseConnection(Connection con, DataSource dataSource) \{  
11.     **try** \{  
12.         doReleaseConnection(con, dataSource);  
13.     \}  
14.     **catch** (SQLException ex) \{  
15.         logger.debug("Could not close JDBC Connection", ex);  
16.     \}  
17.     **catch** (Throwable ex) \{  
18.         logger.debug("Unexpected exception on closing JDBC Connection", ex);  
19.     \}  
20. \}  
21.   
22. /\*\* 
23. \* Actually close the given Connection, obtained from the given DataSource. 
24. \* Same as \{@link \#releaseConnection\}, but throwing the original SQLException. 
25. \* <p>Directly accessed by \{@link TransactionAwareDataSourceProxy\}. 
26. \* @param con the Connection to close if necessary 
27. \* (if this is <code>null</code>, the call will be ignored) 
28. \* @param dataSource the DataSource that the Connection was obtained from 
29. \* (may be <code>null</code>) 
30. \* @throws SQLException if thrown by JDBC methods 
31. \* @see \#doGetConnection 
32. \*/  
33. **public** **static** **void** doReleaseConnection(Connection con, DataSource dataSource) **throws** SQLException \{  
34.     **if** (con == **null**) \{  
35.         **return**;  
36.     \}  
37.   
38.     **if** (dataSource != **null**) \{  
39.         ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);  
40.         **if** (conHolder != **null** && connectionEquals(conHolder, con)) \{  
41.             // It's the transactional Connection: Don't close it.  
42.             conHolder.released();  
43.             **return**;  
44.         \}  
45.     \}  
46.   
47.     // Leave the Connection open only if the DataSource is our  
48.     // special SmartDataSoruce and it wants the Connection left open.  
49.     **if** (!(dataSource **instanceof** SmartDataSource) || ((SmartDataSource) dataSource).shouldClose(con)) \{  
50.         logger.debug("Returning JDBC Connection to DataSource");  
51.         con.close();  
52.     \}  
53. \}

主要下面这几行代码:

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1.  // Leave the Connection open only if the DataSource is our  
2.  // special SmartDataSoruce and it wants the Connection left open.  
3.  **if** (!(dataSource **instanceof** SmartDataSource) || ((SmartDataSource) dataSource).shouldClose(con)) \{  
4.      logger.debug("Returning JDBC Connection to DataSource");  
5.      con.close();  
6.  \}

哦，可以看到大部分情况下是自动关闭，除非你使用的SmartDataSource，且SmartDataSource指定了允许关闭。   
  
  
有些时候，你引入了JdbcTemplate或者DaoSupport，但是有时还需要自己额外的拿到conn进行操作，如下：   
jdbcTemplate.getDataSource().getConnection()   
那么，你应该就需要关闭连接了

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