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本文浅析 spring jdbcTemplate 源码，主要是学习其设计精髓。模板模式、巧妙的回调
一、jdbcTemplate 类结构
①、JdbcOperations : 接口定义了方法，如
<T> T execute(StatementCallback<T> action) throws DataAccessException;
void execute(String sql) throws DataAccessException;
<T> T query(String sql, ResultSetExtractor<T> rse) throws DataAccessException;
。。。
②、JdbcAccessor ： 定义了数据源。
③、实现JdbcOperations接口定义的方法
二、jdbcTemplate 模板模式
1、我们看下execute(StatementCallback<T> action)实现 （核心）
public <T> T execute(StatementCallback<T> action) throws DataAccessException { Assert.notNull(action, "Callback object must not be null"); Connection con = DataSourceUtils.getConnection(getDataSource()); Statement stmt = null; try { Connection conToUse = con; if (this.nativeJdbcExtractor != null && this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) { conToUse = this.nativeJdbcExtractor.getNativeConnection(con); } stmt = conToUse.createStatement(); applyStatementSettings(stmt); Statement stmtToUse = stmt; if (this.nativeJdbcExtractor != null) { stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt); } T result = action.doInStatement(stmtToUse); // 回调 handleWarnings(stmt); return result; } catch (SQLException ex) { JdbcUtils.closeStatement(stmt); stmt = null; DataSourceUtils.releaseConnection(con, getDataSource()); con = null; throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex); } finally { JdbcUtils.closeStatement(stmt); DataSourceUtils.releaseConnection(con, getDataSource()); } }
2、再看下 execute(String sql) 源码
public void execute(final String sql) throws DataAccessException { if (logger.isDebugEnabled()) { logger.debug("Executing SQL statement [" + sql + "]"); } class ExecuteStatementCallback implements StatementCallback<Object>, SqlProvider { @Override public Object doInStatement(Statement stmt) throws SQLException { stmt.execute(sql); // JAVA jdbc return null; } @Override public String getSql() { return sql; } } execute(new ExecuteStatementCallback()); // 调用上述T execute(StatementCallback<T> action) }
由此，可以知道，我们平时常用的execute(final String sql) 方法，底层帮我们做了很多事情，如创建默认的ExecuteStatementCallback，采用回调的方式，由模板去执行sql，关闭链接
3、T query(final String sql, final ResultSetExtractor<T> rse) 源码实现
@Override public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException { Assert.notNull(sql, "SQL must not be null"); Assert.notNull(rse, "ResultSetExtractor must not be null"); if (logger.isDebugEnabled()) { logger.debug("Executing SQL query [" + sql + "]"); } class QueryStatementCallback implements StatementCallback<T>, SqlProvider { @Override public T doInStatement(Statement stmt) throws SQLException { ResultSet rs = null; try { rs = stmt.executeQuery(sql); ResultSet rsToUse = rs; if (nativeJdbcExtractor != null) { rsToUse = nativeJdbcExtractor.getNativeResultSet(rs); } return rse.extractData(rsToUse); } finally { JdbcUtils.closeResultSet(rs); } } @Override public String getSql() { return sql; } } return execute(new QueryStatementCallback()); }
4、update(final String sql) 源码
@Override public int update(final String sql) throws DataAccessException { Assert.notNull(sql, "SQL must not be null"); if (logger.isDebugEnabled()) { logger.debug("Executing SQL update [" + sql + "]"); } class UpdateStatementCallback implements StatementCallback<Integer>, SqlProvider { @Override public Integer doInStatement(Statement stmt) throws SQLException { int rows = stmt.executeUpdate(sql); if (logger.isDebugEnabled()) { logger.debug("SQL update affected " + rows + " rows"); } return rows; } @Override public String getSql() { return sql; } } return execute(new UpdateStatementCallback()); }
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原文地址：http://www.cnblogs.com/chenmo-xpw/p/5536592.html
