调用入口
调用JdbcTemplate提供的API都会委托给execute()，代码如下：
public <T> T execute(PreparedStatementCreator psc, PreparedStatementCallback<T> action)
throws DataAccessException {
Assert.notNull(psc, "PreparedStatementCreator must not be null");
Assert.notNull(action, "Callback object must not be null");
if (logger.isDebugEnabled()) {
String sql = getSql(psc);
logger.debug("Executing prepared SQL statement" + (sql != null ? " [" + sql + "]" : ""));
}
Connection con = DataSourceUtils.getConnection(getDataSource());
PreparedStatement ps = null;
try {
Connection conToUse = con;
if (this.nativeJdbcExtractor != null &&
this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativePreparedStatements()) {
conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
}
ps = psc.createPreparedStatement(conToUse);
applyStatementSettings(ps);
PreparedStatement psToUse = ps;
if (this.nativeJdbcExtractor != null) {
psToUse = this.nativeJdbcExtractor.getNativePreparedStatement(ps);
}
T result = action.doInPreparedStatement(psToUse);
handleWarnings(ps);
return result;
}
catch (SQLException ex) {
// Release Connection early, to avoid potential connection pool deadlock
// in the case when the exception translator hasn't been initialized yet.
if (psc instanceof ParameterDisposer) {
((ParameterDisposer) psc).cleanupParameters();
}
String sql = getSql(psc);
psc = null;
JdbcUtils.closeStatement(ps);
ps = null;
DataSourceUtils.releaseConnection(con, getDataSource());
con = null;
throw getExceptionTranslator().translate("PreparedStatementCallback", sql, ex);
}
finally {
if (psc instanceof ParameterDisposer) {
((ParameterDisposer) psc).cleanupParameters();
}
JdbcUtils.closeStatement(ps);
DataSourceUtils.releaseConnection(con, getDataSource());
}
}
总结一下可以分为三个步骤：
- 获取DataSource的Connection 。
- 设置Statement的属性并执行SQL 。
- 关闭Connection 。
1.获取Connection
Spring jdbcTemplate 获取Connection 是委托给 DataSourceUtils.getConnection(getDataSource());实现的。里面的核心方法就是调用 dataSource.getConnection()获取。
DBCP的getConnection() 内部是通过GenericObjectPool实现的，PoolableConnectionFactory是pool的工厂负责makeObject()：
class BasicDataSource{
protected void createConnectionPool() {
// Create an object pool to contain our active connections
GenericObjectPool gop;
if ((abandonedConfig != null) && (abandonedConfig.getRemoveAbandoned())) {
gop = new AbandonedObjectPool(null,abandonedConfig);
}
else {
gop = new GenericObjectPool();
}
gop.setMaxActive(maxActive);
gop.setMaxIdle(maxIdle);
gop.setMinIdle(minIdle);
gop.setMaxWait(maxWait);
gop.setTestOnBorrow(testOnBorrow);
gop.setTestOnReturn(testOnReturn);
gop.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);
gop.setNumTestsPerEvictionRun(numTestsPerEvictionRun);
gop.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);
gop.setTestWhileIdle(testWhileIdle);
connectionPool = gop;
}
}
2.设置Statement的属性并执行SQL
jdbcTempate有一行比较重要的代码applyStatementSettings(ps) 是设置StatementSettings的,包括FetchSize，MaxRows，QueryTimeout等，在某些情况下非常有用。
protected void applyStatementSettings(Statement stmt) throws SQLException {
int fetchSize = getFetchSize();
if (fetchSize > 0) {
stmt.setFetchSize(fetchSize);
}
int maxRows = getMaxRows();
if (maxRows > 0) {
stmt.setMaxRows(maxRows);
}
DataSourceUtils.applyTimeout(stmt, getDataSource(), getQueryTimeout());
}
3.关闭Connection
执行完SQL之后需要关闭connection，jdbcTempalte是委托给 DataSourceUtils.releaseConnection(con, getDataSource())，最核心还是con.close()
public static void doReleaseConnection(Connection con, DataSource dataSource) throws SQLException {
if (con == null) {
return;
}
if (dataSource != null) {
ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
if (conHolder != null && connectionEquals(conHolder, con)) {
// It's the transactional Connection: Don't close it.
conHolder.released();
return;
}
}
// Leave the Connection open only if the DataSource is our
// special SmartDataSoruce and it wants the Connection left open.
if (!(dataSource instanceof SmartDataSource) || ((SmartDataSource) dataSource).shouldClose(con)) {
logger.debug("Returning JDBC Connection to DataSource");
con.close();
}
}
在dbcp中con实际上是PoolableConnection,其close方法被重写只是把connection返回到pool，没有实际关闭。
public synchronized void close() throws SQLException {
if (_closed) {
// already closed
return;
}
boolean isUnderlyingConectionClosed;
try {
isUnderlyingConectionClosed = _conn.isClosed();
} catch (SQLException e) {
try {
_pool.invalidateObject(this); // XXX should be guarded to happen at most once
} catch(IllegalStateException ise) {
// pool is closed, so close the connection
passivate();
getInnermostDelegate().close();
} catch (Exception ie) {
// DO NOTHING the original exception will be rethrown
}
throw (SQLException) new SQLException("Cannot close connection (isClosed check failed)").initCause(e);
}
if (!isUnderlyingConectionClosed) {
// Normal close: underlying connection is still open, so we
// simply need to return this proxy to the pool
try {
_pool.returnObject(this); // XXX should be guarded to happen at most once
} catch(IllegalStateException e) {
// pool is closed, so close the connection
passivate();
getInnermostDelegate().close();
} catch(SQLException e) {
throw e;
} catch(RuntimeException e) {
throw e;
} catch(Exception e) {
throw (SQLException) new SQLException("Cannot close connection (return to pool failed)").initCause(e);
}
} else {
// Abnormal close: underlying connection closed unexpectedly, so we
// must destroy this proxy
try {
_pool.invalidateObject(this); // XXX should be guarded to happen at most once
} catch(IllegalStateException e) {
// pool is closed, so close the connection
passivate();
getInnermostDelegate().close();
} catch (Exception ie) {
// DO NOTHING, "Already closed" exception thrown below
}
throw new SQLException("Already closed.");
}
}