MyBatis 不使用插件 分页

第一步：创建Maven项目

• 添加Maven依赖：

        junit
        junit
        4.12
        test
    

    
        log4j
        log4j
        1.2.17
    

    
        org.projectlombok
        lombok
        1.18.10
    

    
        mysql
        mysql-connector-java
        8.0.18
    
    
        org.mybatis
        mybatis
        3.5.4
    
    
        org.mybatis
        mybatis-typehandlers-jsr310
        1.0.2
    
    
        com.github.pagehelper
        pagehelper
        5.1.11
    

• 指定Mapper XML文件在mybatis-config.xml中的配置有效，强制部署resources目录到classes

    
        src/main/resources
        
            **/*.xml
        
    
    
        ${basedir}/src/main/resources
    

第二步：配置文件

- log4j.properties
log4j.rootLogger=DEBUG, Console  

#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender  
log4j.appender.Console.layout=org.apache.log4j.PatternLayout  
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n  

log4j.logger.java.sql.ResultSet=INFO  
log4j.logger.org.apache=INFO  
log4j.logger.java.sql.Connection=DEBUG  
log4j.logger.java.sql.Statement=DEBUG  
log4j.logger.java.sql.PreparedStatement=DEBUG  

• mysql.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1/db_test?useSSL=false&serverTimezone=CST
username=root
password=root

• mybatis-config.xml

DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

    
    

    
        
    

    
        
            
        
    

    
        
            
              
                
                
                
                
            
        
    

    
        
    

注意：mappers标签中使用的是resouce

第三步：实体类

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Emp implements Serializable {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private LocalDate hiredate;
    private double sal;
    private double comm;
    private int deptno;
}

第四步：接口文件EmpMapper.java

public interface EmpMapper {
    List selectEmpByPage1();

    List selectEmpByPage2(Map map);
}

第五步：EmpMapper.xml

在resources目录下创建mapper文件夹，然后在该文件夹中创建映射文件EmpMapper.xml：

DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

    
        select * from tb_emp
        
            
                and deptno=#{deptno}
            
            
                and ename=#{ename}
            
            
                and hiredate ]]> #{startDate}
            
            
                and hiredate  #{endDate}
            
        
        order by hiredate desc
        
            limit #{pageNum} , #{pageSize}
        
    

    
      SELECT * from tb_emp
    

第六步：MyBatisUtil

public class MyBatisUtil {
    private static String CONFIG_FILE_LOCATION = "mybatis-config.xml";
    private static final ThreadLocal threadLocal = new ThreadLocal();
    private static SqlSessionFactory sessionFactory;

    static {
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(CONFIG_FILE_LOCATION);
            SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
            sessionFactory = builder.build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSession() { //获取SqlSession
        SqlSession session = threadLocal.get();
        if (session == null) {
            session = (sessionFactory != null) ? sessionFactory.openSession() : null;
            threadLocal.set(session);
        }
        return session;
    }

    public static void closeSession() { //关闭SqlSession
        SqlSession session = threadLocal.get();
        if (session != null) {
            session.close();
            threadLocal.set(null);
        }
    }
}

第七步：测试代码

public class EmpMapperTest {

    private EmpMapper empMapper;

    @Before
    public void before() {
        SqlSession session = MyBatisUtil.getSession(); // 用来执行已映射的SQL语句
        empMapper = session.getMapper(EmpMapper.class);
    }

    @After
    public void after() {
        MyBatisUtil.closeSession();
    }


    @Test
    public void selectEmpByPage() {//求第2页，每页显示3条
        Map map = new HashMap();
        map.put("deptno", 20);
        map.put("startDate", "1987-05-23");
        map.put("endDate", "2018-12-02");
        map.put("pageNum", (2 - 1) * 3);
        map.put("pageSize", 3);
        List list = empMapper.selectEmpByPage2(map);
        list.forEach(System.out::println);
    }

    @Test
    public void fun1() {
        PageHelper.startPage(2, 3);
        List empList = empMapper.selectEmpByPage1();
        for (Emp emp : empList)
            System.out.println(emp);
    }

    @Test
    public void fun3() {
        PageHelper.startPage(2, 3);
        //分页后，实际返回的结果list类型是Page，如果想取出分页信息，需要强制转换为Page
        Page empPage = (Page) empMapper.selectEmpByPage1();
        long total = empPage.getTotal();
        System.out.println(total);//14
        List empList = empPage.getResult();
        empList.forEach(item -> System.out.println(item));
    }
    @Test
    public void fun30() {
        PageHelper.startPage(2, 3);
        //分页后，实际返回的结果list类型是Page，如果想取出分页信息，需要强制转换为Page
        Page empPage = (Page) empMapper.selectEmpByPage1();
        long total = empPage.getTotal();
        System.out.println(total);//14
        List empList = empPage.getResult();
        empList.forEach(item -> System.out.println(item));
    }

    @Test
    public void fun31() {//只分页不统计
        Page page = PageHelper.startPage(2, 3, false);
        empMapper.selectEmpByPage1();

        long total = page.getTotal();
        System.out.println(total);   //-1
        List empList = page.getResult();
        empList.forEach(item -> System.out.println(item));
    }

    @Test
    public void fun32() {//分页的同时做统计
        Page page = PageHelper.startPage(2, 3, true);
        empMapper.selectEmpByPage1();

        long total = page.getTotal();
        System.out.println(total);  //14
        List empList = page.getResult();
        empList.forEach(item -> System.out.println(item));
    }

    @Test
    public void fun4() {
        PageHelper.startPage(2, 3);
        List list = empMapper.selectEmpByPage1();

        PageInfo page = new PageInfo(list);//用PageInfo对结果进行包装
        //测试PageInfo全部分页属性
        System.out.println(page.getPageNum());
        System.out.println(page.getPageSize());
        System.out.println(page.getStartRow());
        System.out.println(page.getEndRow());
        System.out.println(page.getTotal());
        System.out.println(page.getPages());
        System.out.println(page.getNavigateFirstPage());
        System.out.println(page.getNavigateLastPage());
        System.out.println(page.isIsFirstPage());
        System.out.println(page.isIsLastPage());
        System.out.println(page.isHasPreviousPage());
        System.out.println(page.isHasNextPage());
    }

}