一.简述及实现原则

装饰模式：在不改变 原有类 和 不使用继承的情况下， 动态地扩展一个对象的功能。

因会创建一个包装对象，来包裹真实对象而得名。

• 作用：增强对象的功能

例子1：

墙： 功能---遮风挡雨

包了墙纸的墙（本质还是墙）：

功能---遮风挡雨

新增功能---陶冶情操

 

例子2：

钢笔： 功能---写字

包了礼盒的钢笔（本质还是钢笔）：

功能---写字

功能---礼品

1. 没有改变原有类
2. 进行动态地增强

装饰类：增强功能的类（包了墙纸的墙）

被装饰类：待增强功能的类（墙）

实现原则：

1. 装饰类 必须 实现 被装饰类的所有接口
2. 装饰类 中 必须获取 被装饰类对象

二.入门案例

分析：

1. 定义一个装饰类 实现 Phone接口
2. 装饰类中 获取到 被装饰类对象（成员变量）

 

代码实现：

HWPhoneDecorator:

public class HWPhoneDecorator implements Phone {//被装饰类的对象private HWPhone old;public HWPhoneDecorator(HWPhone old) {this.old = old;}/** 打电话方法不需要增强，不需要改变* */public void call(String number) {old.call(number);}/*** 发短信方法需要被增强*/public void sendMsg() {//1、先运行原来的功能old.sendMsg();//2、再执行新的增强代码System.out.println("(o゜▽゜)o☆[BINGO!]");}
}

测试类：

public static void main(String[] args) {Phone hw = new HWPhoneDecorator(new HWPhone());hw.call("12345");hw.sendMsg();
}

小结：

装饰者设计模式，可以在不改变原有类的情况，动态增强类中某个方法。

 

实现：

1. 装饰类实现 被装饰类实现的所有接口
2. 装饰类中 获取  被装饰类对象

三.​​​​​​​装饰者设计模式向静态代理转变

HWPhoneDecorator 

public class HWPhoneDecorator implements Phone {//被装饰类的对象private Phone old;  //接口下的实现类都能增强public HWPhoneDecorator(Phone old) {this.old = old;}/** 打电话方法不需要增强，不需要改变* */public void call(String number) {old.call(number);}/*** 发短信方法需要被增强*/public void sendMsg() {//1、先运行原来的功能old.sendMsg();//2、再执行新的增强代码System.out.println("(o゜▽゜)o☆[BINGO!]");}
}

四.​​​​​​​.使用装饰者设计模式修改连接池

• 增强Connection 对象close方法，不是关闭资源，而是归还连接池

分析：

1. 编写一个装饰类MyConnection，增强Connection对象
2. 需要重写close方法
3. 把连接池创建的Connection对象，装饰为MyConnection对象

MyConnection

public class MyConnection implements Connection {//被装饰的Connection对象private Connection old;//因为close方法需要把连接归还连接池，所以这里也要获取连接池private LinkedList<Connection> pool;public MyConnection(Connection old, LinkedList<Connection> pool) {this.old = old;this.pool = pool;}/*** 要增强的close方法* @throws SQLException*/public void close() throws SQLException {//old.close();//会关闭资源//把当前装饰类对象 归还到连接池pool.addLast(this);}/*** 其他方法 用原对象进行调用即可,底下代码无需手写*/public Statement createStatement() throws SQLException {return old.createStatement();}public PreparedStatement prepareStatement(String sql) throws SQLException {return old.prepareStatement(sql);}public CallableStatement prepareCall(String sql) throws SQLException {return old.prepareCall(sql);}public String nativeSQL(String sql) throws SQLException {return old.nativeSQL(sql);}public void setAutoCommit(boolean autoCommit) throws SQLException {old.setAutoCommit(autoCommit);}public boolean getAutoCommit() throws SQLException {return old.getAutoCommit();}public void commit() throws SQLException {old.commit();}public void rollback() throws SQLException {old.rollback();}public boolean isClosed() throws SQLException {return old.isClosed();}public DatabaseMetaData getMetaData() throws SQLException {return old.getMetaData();}public void setReadOnly(boolean readOnly) throws SQLException {old.setReadOnly(readOnly);}public boolean isReadOnly() throws SQLException {return old.isReadOnly();}public void setCatalog(String catalog) throws SQLException {old.setCatalog(catalog);}public String getCatalog() throws SQLException {return old.getCatalog();}public void setTransactionIsolation(int level) throws SQLException {old.setTransactionIsolation(level);}public int getTransactionIsolation() throws SQLException {return old.getTransactionIsolation();}public SQLWarning getWarnings() throws SQLException {return old.getWarnings();}public void clearWarnings() throws SQLException {old.clearWarnings();}public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {return old.createStatement(resultSetType,resultSetConcurrency);}public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return old.prepareStatement(sql,resultSetType,resultSetConcurrency);}public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return old.prepareCall(sql,resultSetType,resultSetConcurrency);}public Map<String, Class<?>> getTypeMap() throws SQLException {return old.getTypeMap();}public void setTypeMap(Map<String, Class<?>> map) throws SQLException {old.setTypeMap(map);}public void setHoldability(int holdability) throws SQLException {old.setHoldability(holdability);}public int getHoldability() throws SQLException {return old.getHoldability();}public Savepoint setSavepoint() throws SQLException {return old.setSavepoint();}public Savepoint setSavepoint(String name) throws SQLException {return old.setSavepoint(name);}public void rollback(Savepoint savepoint) throws SQLException {old.rollback(savepoint);}public void releaseSavepoint(Savepoint savepoint) throws SQLException {old.releaseSavepoint(savepoint);}public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return old.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);}public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return old.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);}public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return old.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);}public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {return old.prepareStatement(sql,autoGeneratedKeys);}public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {return old.prepareStatement(sql,columnIndexes);}public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {return old.prepareStatement(sql,columnNames);}public Clob createClob() throws SQLException {return old.createClob();}public Blob createBlob() throws SQLException {return old.createBlob();}public NClob createNClob() throws SQLException {return old.createNClob();}public SQLXML createSQLXML() throws SQLException {return old.createSQLXML();}public boolean isValid(int timeout) throws SQLException {return old.isValid(timeout);}public void setClientInfo(String name, String value) throws SQLClientInfoException {old.setClientInfo(name,value);}public void setClientInfo(Properties properties) throws SQLClientInfoException {old.setClientInfo(properties);}public String getClientInfo(String name) throws SQLException {return old.getClientInfo(name);}public Properties getClientInfo() throws SQLException {return old.getClientInfo();}public Array createArrayOf(String typeName, Object[] elements) throws SQLException {return old.createArrayOf(typeName,elements);}public Struct createStruct(String typeName, Object[] attributes) throws SQLException {return old.createStruct(typeName,attributes);}public void setSchema(String schema) throws SQLException {old.setSchema(schema);}public String getSchema() throws SQLException {return old.getSchema();}public void abort(Executor executor) throws SQLException {old.abort(executor);}public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {old.setNetworkTimeout(executor,milliseconds);}public int getNetworkTimeout() throws SQLException {return old.getNetworkTimeout();}public <T> T unwrap(Class<T> iface) throws SQLException {return old.unwrap(iface);}public boolean isWrapperFor(Class<?> iface) throws SQLException {return old.isWrapperFor(iface);}
}

MyDataSource

public class MyDataSource implements DataSource {private static final String DRIVERCLASS="com.mysql.jdbc.Driver";private static final String URL="jdbc:mysql://127.0.0.1:3306/day01_db";private static final String USERNAME="root";private static final String PASSWORD="1234";//连接池private static final LinkedList<Connection> pool = new LinkedList<Connection>();static{//1、注册驱动try {Class.forName(DRIVERCLASS);//2、初始化连接池，默认连接池有5个连接initPool();} catch (Exception e) {e.printStackTrace();}}/*** 初始化连接池*/private static void initPool() throws SQLException {for (int i = 0; i <5 ; i++) {pool.addLast(getCon());}}/*** 类内部进行获取连接的方法* @return*/private static Connection getCon() throws SQLException {return new MyConnection(DriverManager.getConnection(URL,USERNAME,PASSWORD),pool);}/*** 获取连接* @return* @throws SQLException*/public Connection getConnection() throws SQLException {//判断：连接池是否有连接if(pool.size()==0){//连接池没有连接，再创建5个initPool();}//连接池有连接，从池中取出一个连接return pool.removeLast();}/*** 关闭所有资源 （con对象 归还到 连接池中）* @param con* @param ps* @param rs* @throws SQLException*/public static void closeAll(Connection con, PreparedStatement ps,ResultSet rs) throws SQLException {if(rs!=null)rs.close();if(ps!=null)ps.close();if(con!=null)con.close();}public Connection getConnection(String username, String password) throws SQLException {return null;}public <T> T unwrap(Class<T> iface) throws SQLException {return null;}public boolean isWrapperFor(Class<?> iface) throws SQLException {return false;}public PrintWriter getLogWriter() throws SQLException {return null;}public void setLogWriter(PrintWriter out) throws SQLException {}public void setLoginTimeout(int seconds) throws SQLException {}public int getLoginTimeout() throws SQLException {return 0;}public Logger getParentLogger() throws SQLFeatureNotSupportedException {return null;}
}

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