连接池

为什么要有连接池呢？？

因为在数据连接中一个连接的启用和关闭是非常耗费时间的，导致效率不高，所以在实际应用中，我们会创建连接池来提升效率。

先写一个简单自己实现的连接池类，这个不需要编写装饰的connection,但是不规范。

package com.itheima.pool;

import java.sql.Connection;
import java.util.Collections;
import java.util.LinkedList;

import com.itheima.util.DBUtils;
//模拟数据库连接池，但不具备实际开发意义
public class SimpleConnectionPool {
	 //创建一个存放连接的池子
	private static LinkedList<Connection> pool = (LinkedList<Connection>) Collections.synchronizedList(new LinkedList<Connection>());
	
	static{
		try {
			for (int i = 0; i < 10; i++) {
				Connection conn = DBUtils.getConnection();
				pool.add(conn);
			}
		} catch (Exception e) {
			throw new ExceptionInInitializerError("初始化数据库连接失败，请检查配置文件是否正确！");
		}
	}
	
	//得到一个连接
	public static  Connection getConnectionFromPool(){
		Connection conn = null;
		if(pool.size()>0){
			conn =  pool.removeFirst();//从池中取出一个连接
			return conn;
		}else{
			//等待
			//新创建一个连接
			throw new RuntimeException("服务器忙。。。");
		}
		
	}
	//释放资源
	public static  void release(Connection conn){
		pool.addLast(conn);
	}
}

　　然后在通过一个实现datasource接口

package com.itheima.datasource;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Collections;
import java.util.LinkedList;

import javax.sql.DataSource;

import com.itheima.util.DBUtils;

public class MyDataSource implements DataSource{
	 //创建一个存放连接的池子
		private static LinkedList<Connection> pool = (LinkedList<Connection>) Collections.synchronizedList(new LinkedList<Connection>());
		
		static{
			try {
				for (int i = 0; i < 10; i++) {
					Connection conn = DBUtils.getConnection();
					pool.add(conn);
				}
			} catch (Exception e) {
				throw new ExceptionInInitializerError("初始化数据库连接失败，请检查配置文件是否正确！");
			}
		}
	
	public Connection getConnection() throws SQLException {
		Connection conn = null;
		if(pool.size()>0){
			conn =  pool.removeFirst();//从池中取出一个连接
			MyConnection myConn = new MyConnection(conn,pool);//得到一个包装后的MyConnection对象
			return myConn;
		}else{
			//等待
			//新创建一个连接
			throw new RuntimeException("服务器忙。。。");
		}
	}
	
	
	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 void setLogWriter(PrintWriter out) throws SQLException {
		// TODO Auto-generated method stub
		
	}

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

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

	public <T> T unwrap(Class<T> iface) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public boolean isWrapperFor(Class<?> iface) throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	



}

　　因为close方法会把connection关闭，这样导致连接池里面的连接数会变少，所以要写一个自己装饰过的connction类，重写close方法；

package com.itheima.datasource;

import java.sql.Array;
import java.sql.Blob;
import java.sql.CallableStatement;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.NClob;
import java.sql.PreparedStatement;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;
import java.sql.SQLWarning;
import java.sql.SQLXML;
import java.sql.Savepoint;
import java.sql.Statement;
import java.sql.Struct;
import java.util.LinkedList;
import java.util.Map;
import java.util.Properties;

//1、编写一个类，实现与被包装类相同的接口。（具备相同的行为）
//2、定义一个被包装类类型的变量。
//3、定义构造方法，把被包装类的对象注入，给被包装类变量赋值。
//4、对于不需要改写的方法，调用原有的方法。
//5、对于需要改写的方法，写自己的代码
public class MyConnection implements Connection{

	private Connection oldConnection;//com.mysql.jdbc.Connection
	private LinkedList<Connection> pool;//连接池对象
	public MyConnection(Connection oldConnection,LinkedList<Connection> pool){
		this.oldConnection = oldConnection;//得到com.mysql.jdbc.Connection
		this.pool = pool;//得到连接池对象
	}
	
	public void close() throws SQLException {
		pool.addLast(oldConnection);
	}
	
	public PreparedStatement prepareStatement(String sql) throws SQLException {
		return oldConnection.prepareStatement(sql);
	}
	
	public <T> T unwrap(Class<T> iface) throws SQLException {
		return oldConnection.unwrap(iface);
	}

	public boolean isWrapperFor(Class<?> iface) throws SQLException {
		return oldConnection.isWrapperFor(iface);
	}

	public Statement createStatement() throws SQLException {
		return oldConnection.createStatement();
	}



	public CallableStatement prepareCall(String sql) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public String nativeSQL(String sql) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public void setAutoCommit(boolean autoCommit) throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public boolean getAutoCommit() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	public void commit() throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public void rollback() throws SQLException {
		// TODO Auto-generated method stub
		
	}



	public boolean isClosed() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

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

	public void setReadOnly(boolean readOnly) throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public boolean isReadOnly() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	public void setCatalog(String catalog) throws SQLException {
		// TODO Auto-generated method stub
		
	}

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

	public void setTransactionIsolation(int level) throws SQLException {
		// TODO Auto-generated method stub
		
	}

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

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

	public void clearWarnings() throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public Statement createStatement(int resultSetType, int resultSetConcurrency)
			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 CallableStatement prepareCall(String sql, int resultSetType,
			int resultSetConcurrency) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public Map<String, Class<?>> getTypeMap() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public void setHoldability(int holdability) throws SQLException {
		// TODO Auto-generated method stub
		
	}

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

	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 rollback(Savepoint savepoint) throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public void releaseSavepoint(Savepoint savepoint) throws SQLException {
		// TODO Auto-generated method stub
		
	}

	public Statement createStatement(int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			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 CallableStatement prepareCall(String sql, int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			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 Clob createClob() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

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

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

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

	public boolean isValid(int timeout) throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	public void setClientInfo(String name, String value)
			throws SQLClientInfoException {
		// TODO Auto-generated method stub
		
	}

	public void setClientInfo(Properties properties)
			throws SQLClientInfoException {
		// TODO Auto-generated method stub
		
	}

	public String getClientInfo(String name) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

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

	public Array createArrayOf(String typeName, Object[] elements)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public Struct createStruct(String typeName, Object[] attributes)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

}

　　

 终极版，把装饰类细化的更清楚

package com.itheima.warper;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Collections;
import java.util.LinkedList;

import javax.sql.DataSource;

import com.itheima.util.DBUtils;

public class MyDataSource implements DataSource{
	 //创建一个存放连接的池子
		private static LinkedList<Connection> pool = (LinkedList<Connection>) Collections.synchronizedList(new LinkedList<Connection>());
		
		static{
			try {
				for (int i = 0; i < 10; i++) {
					Connection conn = DBUtils.getConnection();
					pool.add(conn);
				}
			} catch (Exception e) {
				throw new ExceptionInInitializerError("初始化数据库连接失败，请检查配置文件是否正确！");
			}
		}
	
	public Connection getConnection() throws SQLException {
		Connection conn = null;
		if(pool.size()>0){
			conn =  pool.removeFirst();//从池中取出一个连接
			MyConnection myConn = new MyConnection(conn,pool);//得到一个包装后的MyConnection对象
			return myConn;
		}else{
			//等待
			//新创建一个连接
			throw new RuntimeException("服务器忙。。。");
		}
	}
	
	
	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 void setLogWriter(PrintWriter out) throws SQLException {
		// TODO Auto-generated method stub
		
	}

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

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

	public <T> T unwrap(Class<T> iface) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public boolean isWrapperFor(Class<?> iface) throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	



}

　　

package com.itheima.warper;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.LinkedList;

public class MyConnection extends MyConnectionWarper {
	private Connection oldConn;
	private LinkedList<Connection> pool;
	public MyConnection(Connection oldConn,LinkedList<Connection> pool) {
		super(oldConn);
		this.oldConn = oldConn;
		this.pool = pool;
	}
	@Override
	public void close() throws SQLException {
		pool.addLast(oldConn);
	}
	
	
	

}