JdbcTemplate 使用了模版模式和回调函数：

1.T execute(ConnectionCallback<T> action) 主要结构 使用了ConnectionCallback中的方法作为回调方法 public <T> T execute(ConnectionCallback<T> action) {    Connection con = DataSourceUtils.getConnection(getDataSource());            Connection conToUse = con;            if (this.nativeJdbcExtractor != null) {                // Extract native JDBC Connection, castable to OracleConnection or the like.                conToUse = this.nativeJdbcExtractor.getNativeConnection(con);            }            else {                // Create close-suppressing Connection proxy, also preparing returned Statements.                conToUse = createConnectionProxy(con);            }            return action.doInConnection(conToUse);        } } 2. T execute(StatementCallback<T> action) public <T> T execute(StatementCallback<T> action) throws DataAccessException {            Connection con = DataSourceUtils.getConnection(getDataSource());            Statement stmt = null;            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);            handleWarnings(stmt);            return result;｝3. execute(final String sql) ：使用内部类的回调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);                return null;            }            @Override            public String getSql() {                return sql;            }        }        execute(new ExecuteStatementCallback());    }