JDBC 06: 连接池 / 数据源

 0.          什么是连接池 / 数据源？

　　　　连接池是一个集合, 用来保存多个连接(Connection)

１．　　为什么需要连接池/数据源？

　　　　＜１＞　　为了避免重复地创建Connection

　　　　＜ 2 ＞       节约资源

2.　　　　创建连接池 / 数据源

public class JDBCUtils {

    private static final String connectionURL = "jdbc:mysql://localhost:3306/web01?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "root";
    
    private static ArrayList<Connection> conlist = new ArrayList<Connection>();
    static {
        for(int i=0;i<5;i++) { // 连接池的容量为5
            Connection con = createConnection();
            conlist.add(con);
        }
    }
    public static Connection getConnection() {
        if(conlist.isEmpty() == false) { 
            Connection con = conlist.get(0); 
            conlist.remove(con);
            return con; // 连接借用
        }else {
            return createConnection();
        }
    }
    private static Connection createConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            return DriverManager.getConnection(connectionURL,username,password);
        }catch(Exception e) {
            e.printStackTrace();
        }
        
        return null;
    }
    private static void closeConnection(Connection con) {
        conlist.add(con); // 连接归还
    }
}    

3. 第三方连接池 - dbcp

public class DOCPDataSource {
    private static final String connectionURL = "jdbc:mysql://localhost:3306/web01?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "root";
    
    private static BasicDataSource ds;
    
    static {
        // 初始化dbcp 数据源
        BasicDataSource ds = new BasicDataSource();
        ds.setDriverClassName("com.mysql.jdbc.Driver");
        ds.setUrl(connectionURL);
        ds.setUsername(username);
        ds.setPassword(password);
        
        ds.setInitialSize(5); // 初始连接个数:    5
        ds.setMaxTotal(20);   // 允许最大连接个数: 20
        ds.setMinIdle(3);     // 设置最少连接个数: 3
    }
    
    public Connection getConnection() {
        try {
            return ds.getConnection(); // 通过dbcp得到的连接,不需要归还,直接close就可以
        }catch(SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
    
    private static void closeConnection(Connection con) {
        try {
            if(con!=null) {
                con.close(); // 这里会把连接归还給dbcp连接池,并不是真正的断开连接
            }
        } catch(SQLException e) {
            e.printStackTrace();
        }
        
    }
}

4. 第三方连接池  - C3P0

package com.Jasper2003.jdbc01;

import java.beans.PropertyVetoException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;


import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3P0DataSource {
    
    private static final String connectionURL = "jdbc:mysql://localhost:3306/web01?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "root";
    
    private static ComboPooledDataSource ds;
    
    static {
        try {
            ds = new ComboPooledDataSource();
            ds.setDriverClass("com.mysql.jdbc.Driver");
            ds.setJdbcUrl(connectionURL);
            ds.setUser(username);
            ds.setPassword(password);
            
            ds.setInitialPoolSize(5); // 初始连接个数:    5
            ds.setMaxPoolSize(20);   // 允许最大连接个数: 20
        }catch(PropertyVetoException e) {
            e.printStackTrace();
        }
    }
    
    public static Connection getConnection() {
        try {
            return ds.getConnection(); 
        }catch(SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
    
    private static void closeConnection(Connection con) {
        try {
            if(con!=null) {
                con.close(); 
            }
        } catch(SQLException e) {
            e.printStackTrace();
        }
    }
    
    public static void close(ResultSet rs, Statement stmt, Connection con) {
        closeResultSet(rs);
        closeStatement(stmt);
        closeConnection(con);
    }
    
    public static void close(Statement stmt1,Statement stmt2, Connection con) {

        closeStatement(stmt1);
        closeStatement(stmt2);
        closeConnection(con);
        
    }
    
    private static void closeResultSet(ResultSet rs) {
        try {
            if(rs!=null)
                rs.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    private static void closeStatement(Statement stmt) {
        try {
            if(stmt!=null)
                stmt.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}