设计模式课程 设计模式精讲 15-3 桥接模式源码解析

1　　　　桥接模式源码解析

1.1　　源码解析1 jdk中的应用（驱动类）

1　　　　桥接模式源码解析

1.1　　源码解析1 jdk中的应用（驱动类）

步骤：

class.forName 调取驱动接口的静态块，触发驱动管理类DriverManager 的注册驱动方法，从而将该驱动放到CopyOnWriteArrayList中。

getConnect方法是通过传入url用户名密码。

针对不同的数据库，通过driverManager中的不同方法，获取的都是相同的接口，jdbc在最初的时候设计了一套接口，再由各个数据库公司实现这套接口。

重点：

实现（各种Driver如SqlDriver，OracleDriver等）和抽象（DriverManager的分离）分离

驱动接口：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.mysql.jdbc;

import java.sql.DriverManager;
import java.sql.SQLException;

public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    public Driver() throws SQLException {
    }
//class.forName 直接调用该静态块
    static {
        try {
            DriverManager.registerDriver(new Driver());
        } catch (SQLException var1) {
            throw new RuntimeException("Can't register driver!");
        }
    }
}

驱动实现类：

public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    public Driver() throws SQLException {
    }
}

DriverManager：

public class DriverManager {
    // List of registered JDBC drivers
    private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<DriverInfo>();
    private static volatile int loginTimeout = 0;
    private static volatile java.io.PrintWriter logWriter = null;
    private static volatile java.io.PrintStream logStream = null;
    // Used in println() to synchronize logWriter
    private final static  Object logSync = new Object();

    /* Prevent the DriverManager class from being instantiated. */
    private DriverManager(){}

 /**
    *内部类，对driver进行封装
    */
class DriverInfo {

    final Driver driver;
    DriverInfo(Driver driver) {
        this.driver = driver;
    }

    public boolean equals(Object other) {
        return (other instanceof DriverInfo)
                && this.driver == ((DriverInfo) other).driver;
    }

    public int hashCode() {
        return driver.hashCode();
    }

    public String toString() {
        return ("driver[className="  + driver + "]");
    }
}

//注册驱动的方法

public static synchronized void registerDriver(java.sql.Driver driver)
    throws SQLException {

    /* Register the driver if it has not already been added to our list */
    if(driver != null) {
        registeredDrivers.addIfAbsent(new DriverInfo(driver));
    } else {
        // This is for compatibility with the original DriverManager
        throw new NullPointerException();
    }

    println("registerDriver: " + driver);
}

//获取数据库连接

@CallerSensitive
public static Connection getConnection(String url,
    String user, String password) throws SQLException {
    java.util.Properties info = new java.util.Properties();

    if (user != null) {
        info.put("user", user);
    }
    if (password != null) {
        info.put("password", password);
    }

    return (getConnection(url, info, Reflection.getCallerClass()));
}
}