最终：但是这种方式行不通，通过查看JDBC工具类获取连接的方法我们发现：我们虽然自定义了一个子类，完成了归还连接的操作 。但是获取的还是这个对象，并不是我们的子类对象 。而我们又不能整体去修改驱动包中类的功能！
（2）用装饰设计模式去解决
/*自定义Connection类 。通过装饰设计模式，实现和mysql驱动包中的Connection实现类相同的功能！实现步骤：1.定义一个类，实现Connection接口2.定义Connection连接对象和连接池容器对象的变量3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值4.在close()方法中，完成连接的归还5.剩余方法，只需要调用mysql驱动包的连接对象完成即可*/public class MyConnection2 implements Connection {//2.定义Connection连接对象和连接池容器对象的变量private Connection con;private List pool;//3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值public MyConnection2(Connection con,List pool) {this.con = con;this.pool = pool;}//4.在close()方法中，完成连接的归还@Overridepublic void close() throws SQLException {pool.add(con);}//注意下面代码的有返回值，自动生成后需要修改返回值 。@Overridepublic Statement createStatement() throws SQLException {return con.createStatement();}@Overridepublic PreparedStatement prepareStatement(String sql) throws SQLException {return con.prepareStatement(sql);}@Overridepublic CallableStatement prepareCall(String sql) throws SQLException {return con.prepareCall(sql);}@Overridepublic String nativeSQL(String sql) throws SQLException {return con.nativeSQL(sql);}@Overridepublic void setAutoCommit(boolean autoCommit) throws SQLException {con.setAutoCommit(autoCommit);}@Overridepublic boolean getAutoCommit() throws SQLException {return con.getAutoCommit();}@Overridepublic void commit() throws SQLException {con.commit();}@Overridepublic void rollback() throws SQLException {con.rollback();}@Overridepublic boolean isClosed() throws SQLException {return con.isClosed();}@Overridepublic DatabaseMetaData getMetaData() throws SQLException {return con.getMetaData();}@Overridepublic void setReadOnly(boolean readOnly) throws SQLException {con.setReadOnly(readOnly);}@Overridepublic boolean isReadOnly() throws SQLException {return con.isReadOnly();}@Overridepublic void setCatalog(String catalog) throws SQLException {con.setCatalog(catalog);}@Overridepublic String getCatalog() throws SQLException {return con.getCatalog();}@Overridepublic void setTransactionIsolation(int level) throws SQLException {con.setTransactionIsolation(level);}@Overridepublic int getTransactionIsolation() throws SQLException {return con.getTransactionIsolation();}@Overridepublic SQLWarning getWarnings() throws SQLException {return con.getWarnings();}@Overridepublic void clearWarnings() throws SQLException {con.clearWarnings();}@Overridepublic Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {return con.createStatement(resultSetType,resultSetConcurrency);}@Overridepublic PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return con.prepareStatement(sql,resultSetType,resultSetConcurrency);}@Overridepublic CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return con.prepareCall(sql,resultSetType,resultSetConcurrency);}@Overridepublic Map> getTypeMap() throws SQLException {return con.getTypeMap();}@Overridepublic void setTypeMap(Map> map) throws SQLException {con.setTypeMap(map);}@Overridepublic void setHoldability(int holdability) throws SQLException {con.setHoldability(holdability);}@Overridepublic int getHoldability() throws SQLException {return con.getHoldability();}@Overridepublic Savepoint setSavepoint() throws SQLException {return con.setSavepoint();}@Overridepublic Savepoint setSavepoint(String name) throws SQLException {return con.setSavepoint(name);}@Overridepublic void rollback(Savepoint savepoint) throws SQLException {con.rollback(savepoint);}@Overridepublic void releaseSavepoint(Savepoint savepoint) throws SQLException {con.releaseSavepoint(savepoint);}@Overridepublic Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);}@Overridepublic PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);}@Overridepublic CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);}@Overridepublic PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {return con.prepareStatement(sql,autoGeneratedKeys);}@Overridepublic PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {return con.prepareStatement(sql,columnIndexes);}@Overridepublic PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {return con.prepareStatement(sql,columnNames);}@Overridepublic Clob createClob() throws SQLException {return con.createClob();}@Overridepublic Blob createBlob() throws SQLException {return con.createBlob();}@Overridepublic NClob createNClob() throws SQLException {return con.createNClob();}@Overridepublic SQLXML createSQLXML() throws SQLException {return con.createSQLXML();}@Overridepublic boolean isValid(int timeout) throws SQLException {return con.isValid(timeout);}@Overridepublic void setClientInfo(String name, String value) throws SQLClientInfoException {con.setClientInfo(name,value);}@Overridepublic void setClientInfo(Properties properties) throws SQLClientInfoException {con.setClientInfo(properties);}@Overridepublic String getClientInfo(String name) throws SQLException {return con.getClientInfo(name);}@Overridepublic Properties getClientInfo() throws SQLException {return con.getClientInfo();}@Overridepublic Array createArrayOf(String typeName, Object[] elements) throws SQLException {return con.createArrayOf(typeName,elements);}@Overridepublic Struct createStruct(String typeName, Object[] attributes) throws SQLException {return con.createStruct(typeName,attributes);}@Overridepublic void setSchema(String schema) throws SQLException {con.setSchema(schema);}@Overridepublic String getSchema() throws SQLException {return con.getSchema();}@Overridepublic void abort(Executor executor) throws SQLException {con.abort(executor);}@Overridepublic void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {con.setNetworkTimeout(executor,milliseconds);}@Overridepublic int getNetworkTimeout() throws SQLException {return con.getNetworkTimeout();}@Overridepublic T unwrap(Class iface) throws SQLException {return con.unwrap(iface);}@Overridepublic boolean isWrapperFor(Class