Mybatis源码解析：JDBC用法一览

JDBC相关的基础知识

在正式分析mybatis源码之前，我们需要对JDBC的api有一个比较清晰的认识，因为mybatis就是基于JDBC的封装，理解了这些常用的api，能提高我们阅读源码的速度。

JDBC的所有编程接口包含在java.sql和javax.sql这2个包中

我们可以通过如下两种方式获取JDBC的Connection对象

1. 通过JDBC api提供的DriverManager类来获取
2. 通过DataSource接口的实现类来获取（主要就是利用池的机制来复用连接，提供系统性能）

Statement：定义了执行SQL语句的方法，这些方法不支持参数输入
PreparedStatement：增加了设置SQL参数的方法
CallableStatement：增加了调用存储过程以及检索存储过程调用结果的方法

使用JDBC进行开发

在MySQL下面建立一个test的库，接着就是创建表和插入记录

create table user_info
(
  id  int auto_increment comment '用户id' primary key,
  name varchar(255) not null comment '用户名',
  age int not null comment '年龄'
);


INSERT INTO `user_info`(`name`, `age`) VALUES ('1', 1);
INSERT INTO `user_info`(`name`, `age`) VALUES ('2', 2);
INSERT INTO `user_info`(`name`, `age`) VALUES ('3', 3);

pom文件中加入加入mysql依赖

<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<version>5.1.35</version>
	<scope>runtime</scope>
</dependency>

Statement语句是SQL语句的描述，使用它可以操作各种SQL语句，包括DDL（数据定义语句，如创建表）DML（CRUD）和DCL（修改权限）等

ResultSet用来获取SQL语句的查询结果

通过DriverManager来获取连接

Connection connection = DriverManager.getConnection("jdbc:mysql://myhost/test?useUnicode=true&characterEncoding=utf-8&useSSL=false", "test", "test");
String sql = "select id, name, age from user_info";
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()) {
    int id = rs.getInt(1);
    String name = rs.getString(2);
    String email = rs.getString(3);
    System.out.println(id + "," + name + "," + email);
}
connection.close();

通过DataSource来获取连接

Map<String, Object> configMap = new HashMap<>();
configMap.put("driverClassName", "com.mysql.jdbc.Driver");
configMap.put("url", "jdbc:mysql://myhost/test?useUnicode=true&characterEncoding=utf-8&useSSL=false");
configMap.put("username", "test");
configMap.put("password", "test");
configMap.put("initialSize", "5");
configMap.put("maxActive", "10");
DataSource dataSource = DruidDataSourceFactory.createDataSource(configMap);
Connection connection = dataSource.getConnection();
String sql = "select id, name, age from user_info";
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()) {
    int id = rs.getInt(1);
    String name = rs.getString(2);
    String email = rs.getString(3);
    System.out.println(id + "," + name + "," + email);
}
connection.close();

PreparedStatement在Statement的基础上提供了使用？作为参数占位符的功能，并且提供了相应的方法为参数占位符设值

Connection connection = DriverManager.getConnection("jdbc:mysql://myhost/test?useUnicode=true&characterEncoding=utf-8&useSSL=false", "test", "test");
String sql = "insert user_info(name, age) values (?, ?)";
PreparedStatement pstmt = connection.prepareStatement(sql);
pstmt.setString(1, "testName");
pstmt.setInt(2, 10);
pstmt.execute();
connection.close();

CallableStatement

CallableStatement继承PreparedStatement，提供了调用存储过程的能力

1. 调用简单的存储过程
2. 调用有输入参数的存储过程
3. 调用有输入输出参数的存储过程

先在数据中执行如下sql创建表和存储过程

-- 创建表
CREATE TABLE `kf_user_info` (
  `id` int(11) NOT NULL COMMENT '用户id',
  `gid` int(11) NOT NULL COMMENT '客服组id',
  `name` varchar(25) NOT NULL COMMENT '客服名字'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='客户信息表';

-- 存储过程如果存在则删除
DROP PROCEDURE IF EXISTS create_kf_use_arg;
-- 定义存储过程
DELIMITER //
CREATE PROCEDURE create_kf_use_arg(IN loop_times INT)
BEGIN
    DECLARE var INT;
    SET var = 1;
    WHILE var <= loop_times DO
    INSERT INTO kf_user_info (`id`,`gid`,`name`)
    VALUES (var, var, var);
    SET var = var + 1;
    END WHILE;
END //
DELIMITER ;

DROP PROCEDURE IF EXISTS get_kf;
DELIMITER //
CREATE PROCEDURE get_kf(IN num int)
BEGIN
    SELECT `id`,`gid`,`name` FROM kf_user_info kf_user_info WHERE id = num;
END //
DELIMITER ;

Connection connection = DriverManager.getConnection("jdbc:mysql://myhost/test?useUnicode=true&characterEncoding=utf-8&useSSL=false", "root", "XpFNhfrEM6eIlRB1");
// 插入5条记录
CallableStatement cs = connection.prepareCall("call create_kf_use_arg(5)");
cs.execute();
// 获取id=5的记录
cs = connection.prepareCall("call get_kf(5)");
cs.execute();
ResultSet rs = cs.getResultSet();
while(rs.next()) {
    int id = rs.getInt(1);
    String name = rs.getString(2);
    String email = rs.getString(3);
    System.out.println(id + "," + name + "," + email);
}
connection.close();

参考博客

[1]http://study.163.com/course/courseMain.htm?courseId=645004