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); } });
