在JavaEE中使用Mybatis框架

MyBatis 使用简单的 XML 或注解用于配置和原始映射，将接口和 Java 的 POJOs（Plain Old Java Objects，普通的 Java 对象）映射成数据库中的记录。每个 MyBatis 应用程序主要都是使用 SqlSessionFactory 实例的，一个 SqlSessionFactory 实例可以通过 SqlSessionFactoryBuilder 获得。SqlSessionFactoryBuilder 可以从一个 xml 配置文件或者一个预定义的配置类的实例获得。

使用框架就是引用别人封装好的 jar 包，按照别人规定好的方式进行配置并调用 jar 包里的各种方法。那 Mybatis 需要进行哪些配置呢？我们来看一个例子：

一、创建简单的 POJO 类

package com.wenji.entity;

public class Employee {
       private int id;
       private String firstName;
       private String lastName;
       private int salary;  

       public Employee() {}
       public Employee(int id,String firstName, String lastName, int salary) {
          this.id = id;
          this.firstName = firstName;
          this.lastName = lastName;
          this.salary = salary;
       }
       //省略getter、setter方法
}

Employee类

二、设置 mybatis 配置文件: Configure.xml（文件名随便起）, 在 src/config 目录下建立此文件，内容如下:

<?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
     <typeAliases>
         <typeAlias type="com.wenji.entity.Employee" alias="Employee"/>
     </typeAliases>

     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
                 <property name="driver" value="oracle.jdbc.driver.OracleDriver"></property>
                 <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl"></property>
                 <property name="username" value="system"></property>
                 <property name="password" value="123456"></property>
             </dataSource>
         </environment>
     </environments>
     <mappers>
         <mapper resource="com/wenji/mapping/Employee.xml"></mapper>
    </mappers>
</configuration>

三、设置 Mybatis 映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.wenji.UserMapper">
    <select id="GetEmployeeByID" parameterType="int" resultType="Employee">
        select id,first_name firstName,last_name lastName,salary from HTCPP.Employee where id = #{id}
    </select>
</mapper>

下面是对这两个配置文件一点解释说明：
1、配置文件 Configure.xml 是 mybatis 用来建立 sessionFactory，里面主要包含了数据库连接相关内容，还有 java 类所对应的别名，比如：<typeAlias type="com.wenji.entity.Employee" alias="Employee"/>  这个别名非常重要，在具体的类的映射中，比如： Employee.xml 中 resultType 就是对应这个。要保持一致，这里的 resultType 还有另外单独的定义方式，后面我们再详细介绍说明。
2、Configure.xml 里面的 <mapper resource="com/wenji/mapping/Employee.xml"></mapper> 是包含要映射的类的 xml 配置文件。
3、在 Employee.xml  文件里面主要是定义各种 SQL 语句，以及这些语句的参数，以及要返回的类型等等。

四、测试是否成功

package com.wenji.test;

import java.util.List;
import java.util.Date;
import java.util.Iterator; 

import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.wenji.entity.Employee;

public class ManageEmployee {
    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;

    static {
        try {
            reader = Resources.getResourceAsReader("configure.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static SqlSessionFactory getSession() {
        return sqlSessionFactory;
    }
    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        SqlSession session = sqlSessionFactory.openSession();
        try {
            Employee employee = (Employee) session.selectOne(
                    "com.wenji.UserMapper.GetEmployeeByID", 2);
            if(employee!=null){
                System.out.println("First Name: " + employee.getFirstName());
                System.out.println("Last Name: " + employee.getLastName());
                System.out.println("Salary: " + employee.getSalary());
            }
        } finally {
            session.close();
        }
    }
}

Mybatis 也提供了注解的方式来定义映射，来看下面这个示例

Employee 类不变，Employee.xml 文件不见了，取而代之的是 IEmployee.java 接口

package com.wenji.dao;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.wenji.entity.Employee;

public interface IEmployee {
    @Select("select id,first_name firstName,last_name lastName,salary from Employee where id = #{id3}")
    public Employee getEmployeeByID(int id2);

    @Select("select id,first_name firstName,last_name lastName,salary from Employee ")
    public List<Employee> getEmployeeList();

    @Insert(" INSERT INTO Employee(id,first_name, last_name,salary) VALUES(#{id}, #{firstName}, #{lastName}, #{salary})")
    public void insertEmployee(Employee ee);

    @Update("UPDATE Employee SET id=#{id},first_name = #{firstName},last_name = #{lastName},salary = #{salary} WHERE id =#{id}")
    public void updateEmployee(Employee ee);

    @Delete("DELETE FROM Employee WHERE id = #{id}")
    public void  deleteEmployee(int id);
}

因为不存在 Employee.xml，所以配置文件只是注释掉一行

<?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
         <typeAlias type="com.wenji.entity.Employee" alias="Employee"/>
<!--         <package name="entity"></package> -->
     </typeAliases>

     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
                 <property name="driver" value="oracle.jdbc.driver.OracleDriver"></property>
                 <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl"></property>
                 <property name="username" value="developer"></property>
                 <property name="password" value="developer"></property>
             </dataSource>
         </environment>
     </environments>
     <mappers>
<!--          <mapper resource="com/wenji/mapping/Employee.xml"></mapper> -->
    </mappers>
</configuration>

测试方法有很大的不同

package com.wenji.test;

import java.util.List;
import java.util.Date;
import java.util.Iterator; 

import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.wenji.dao.IEmployee;
import com.wenji.entity.Employee;

public class ManageEmployee {
    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;
    static {
        try {
            reader = Resources.getResourceAsReader("configure.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            sqlSessionFactory.getConfiguration().addMapper(IEmployee.class);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSessionFactory getSession() {
        return sqlSessionFactory;
    }

    public static void main(String[] args) {
        getEmployeeByID(1);
//        getEmployeeList();
//        testInsert();
//        testUpdate();
//        testDelete();
    }

    private static void getEmployeeByID(int id){
         SqlSession session = sqlSessionFactory.openSession();
         try {
             IEmployee iEmployee = session.getMapper(IEmployee.class);
             Employee employee = iEmployee.getEmployeeByID(id);
             System.out.print("First Name: " + employee.getFirstName());
             System.out.print("  Last Name: " + employee.getLastName());
             System.out.println("  Salary: " + employee.getSalary());
         } finally {
             session.close();
         }
    }

    private static void  getEmployeeList(){
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IEmployee iEmployee = session.getMapper(IEmployee.class);
            List<Employee> employees = iEmployee.getEmployeeList();
            printEmployees(employees);
        } finally {
            session.close();
        }
    }

    public static void testInsert(){
        try{
            // 获取Session连接
            SqlSession session = sqlSessionFactory.openSession();
            // 获取Mapper
            IEmployee eMapper = session.getMapper(IEmployee.class);
            System.out.println("Test insert start...");
            // 执行插入
            Employee ee = new Employee();
            ee.setId(5);
            ee.setFirstName("zhang");
            ee.setLastName("san");
            ee.setSalary(100);
            eMapper.insertEmployee(ee);
            // 提交事务
            session.commit();

            // 显示插入之后Employee信息
            System.out.println("After insert");
            getEmployeeList();
            System.out.println("Test insert finished...");
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    public static void testUpdate(){
        try{
            SqlSession session = sqlSessionFactory.openSession();
            IEmployee eMapper = session.getMapper(IEmployee.class);
            System.out.println("Test update start...");
            printEmployees(eMapper.getEmployeeList());
            // 执行更新
            Employee ee = eMapper.getEmployeeByID(5);
            ee.setFirstName("New name");
            eMapper.updateEmployee(ee);
            // 提交事务
            session.commit();
            // 显示更新之后Employee信息
            System.out.println("After update");
            getEmployeeList();
            System.out.println("Test update finished...");
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    // 删除用户信息
    public static void testDelete(){
        try{
            SqlSession session = sqlSessionFactory.openSession();
            IEmployee eMapper = session.getMapper(IEmployee.class);
            System.out.println("Test delete start...");
            // 显示删除之前Employee信息
            System.out.println("Before delete");
            getEmployeeList();
            // 执行删除
            eMapper.deleteEmployee(5);
            // 提交事务
            session.commit();
            // 显示删除之后User信息
            System.out.println("After delete");
            getEmployeeList();
            System.out.println("Test delete finished...");
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    /**
     *
     * 打印用户信息到控制台
     *
     * @param users
     */
    private static void printEmployees(final List<Employee> employees) {
        for (Employee employee : employees) {
            System.out.print("id: " + employee.getId());
            System.out.print("First Name: " + employee.getFirstName());
            System.out.print("  Last Name: " + employee.getLastName());
            System.out.println("  Salary: " + employee.getSalary());
        }
    }
}