当一个方法满足不了需求时的三种办法

1，写一个子类，重写该方法，这种方式用的很少

2，使用包装设计模式，下面是自己写的一个数据库连接池，明显close（）方法满足不了需求，因为如果用数据库驱动返回来的Connect对象关闭的话，connnect就会返回给数据库，而不是返回给连接池，代码如下：

package cn.itcast.utils;

import java.io.PrintWriter;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.SQLWarning;
import java.sql.Savepoint;
import java.sql.Statement;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Properties;

import javax.sql.DataSource;

public class JdbcPool implements DataSource {

    private static LinkedList<Connection> list = new LinkedList<Connection>();
    private static Properties config = new Properties();
    static{
        try {
            config.load(JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties"));
            
            Class.forName(config.getProperty("driver"));
            for(int i=0;i<10;i++){
                Connection conn = DriverManager.getConnection(config.getProperty("url"), config.getProperty("username"), config.getProperty("password"));
                list.add(conn);
            }
        } catch (Exception e) {
            throw new ExceptionInInitializerError(e);
        }
    }
    
    
    //conn.close()
    /* 在实际开发，发现对象的方法满足不了开发需求时，有三种方式对其进行增强
     * 1.写一个connecton子类，覆盖close方法，增强close方法
     * 2.用包装设计模式
     * 3.用动态代理    aop 面向切面编程
     */
    public Connection getConnection() throws SQLException {
        
        if(list.size()<=0){
            throw new RuntimeException("数据库忙，请稍会再来！！");
        }
        Connection conn = list.removeFirst();   //mysqlconnection   C
        MyConnection my = new MyConnection(conn);
         return my;      //my-------preparedStatment   commit   createStatement  close
    }
    

    //1.定义一个类，实现与被增强相同的接口
    //2.在类中定义一个变量，记住被增强对象
    //3.定义一个构造函数，接收被增强对象
    //4.覆盖想增强的方法
    //5.对于不想增强的方法，直接调用目标对象（被增强对象）的方法
    
    class MyConnection implements Connection{
        private Connection conn;
        public MyConnection(Connection conn){
            this.conn = conn;
        }
        public void close(){
            list.add(this.conn);
        }
        public void clearWarnings() throws SQLException {
            this.conn.clearWarnings();
            
        }
        public void commit() throws SQLException {
            this.conn.commit();
            
        }
        public Statement createStatement() throws SQLException {
            return this.conn.createStatement();
        }
        public Statement createStatement(int resultSetType,
                int resultSetConcurrency, int resultSetHoldability)
                throws SQLException {
            return this.conn.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability);
        }
        public Statement createStatement(int resultSetType,
                int resultSetConcurrency) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public boolean getAutoCommit() throws SQLException {
            // TODO Auto-generated method stub
            return false;
        }
        public String getCatalog() throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public int getHoldability() throws SQLException {
            // TODO Auto-generated method stub
            return 0;
        }
        public DatabaseMetaData getMetaData() throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public int getTransactionIsolation() throws SQLException {
            // TODO Auto-generated method stub
            return 0;
        }
        public Map<String, Class<?>> getTypeMap() throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public SQLWarning getWarnings() throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public boolean isClosed() throws SQLException {
            // TODO Auto-generated method stub
            return false;
        }
        public boolean isReadOnly() throws SQLException {
            // TODO Auto-generated method stub
            return false;
        }
        public String nativeSQL(String sql) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public CallableStatement prepareCall(String sql, int resultSetType,
                int resultSetConcurrency, int resultSetHoldability)
                throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public CallableStatement prepareCall(String sql, int resultSetType,
                int resultSetConcurrency) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public CallableStatement prepareCall(String sql) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql,
                int resultSetType, int resultSetConcurrency,
                int resultSetHoldability) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql,
                int resultSetType, int resultSetConcurrency)
                throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql,
                int autoGeneratedKeys) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql,
                int[] columnIndexes) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql,
                String[] columnNames) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public PreparedStatement prepareStatement(String sql)
                throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public void releaseSavepoint(Savepoint savepoint) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void rollback() throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void rollback(Savepoint savepoint) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void setAutoCommit(boolean autoCommit) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void setCatalog(String catalog) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void setHoldability(int holdability) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void setReadOnly(boolean readOnly) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public Savepoint setSavepoint() throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public Savepoint setSavepoint(String name) throws SQLException {
            // TODO Auto-generated method stub
            return null;
        }
        public void setTransactionIsolation(int level) throws SQLException {
            // TODO Auto-generated method stub
            
        }
        public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
            // TODO Auto-generated method stub
            
        }
    }
    
    
    

    public Connection getConnection(String username, String password)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    public PrintWriter getLogWriter() throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    public int getLoginTimeout() throws SQLException {
        // TODO Auto-generated method stub
        return 0;
    }

    public void setLogWriter(PrintWriter arg0) throws SQLException {
        // TODO Auto-generated method stub

    }

    public void setLoginTimeout(int arg0) throws SQLException {
        // TODO Auto-generated method stub

    }

}

3.使用动态代理

proxyConn = (Connection) Proxy.newProxyInstance(this.getClass()
            .getClassLoader(), conn.getClass().getInterfaces(),
            new InvocationHandler() {
        //此处为内部类，当close方法被调用时将conn还回池中,其它方法直接执行
            public Object invoke(Object proxy, Method method,
                      Object[] args) throws Throwable {
                if (method.getName().equals("close")) {
                    pool.addLast(conn);
                    return null;
            }
            return method.invoke(conn, args);
        }
    });