7.MyBatis延时加载

1.创建javaWeb项目MyBatis_Lazy并在WebRoot下的WEB-INF下的lib下添加如下jar文件

cglib-nodep-2.1_3.jar

log4j-1.2.17.jar

mybatis-3.2.3.jar

ojdbc14.jar

2.在src下创建log4j.properties日志文件

 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   

log4j.properties

3.在src下创建jdbc.properties数据库属性文件

 driver=oracle.jdbc.driver.OracleDriver
 url=jdbc\:oracle\:thin\:@127.0.0.1\:1521\:orcl
 username=scott
 password=tiger

jdbc.properties

4.在src下创建Configuration.xml主配置文件

 <?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>
    <!-- 1.jdbc链接数据库的主配置文件 -->
    <properties resource="jdbc.properties"/>

    <!-- 2.全局参数配置 -->
    <settings>
         <!--打开延迟加载的开关  -->
         <setting name="lazyLoadingEnabled" value="true"/>
          <!--将积极加载改为消极加载及按需加载  -->
         <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <!-- 别名配置 -->
    <typeAliases>
      <typeAlias type="com.entity.Dept" alias="Dept"/>
      <typeAlias type="com.entity.Emp" alias="Emp"/>
    </typeAliases>

    <!-- 3.数据源的配置 -->
    <environments default="development">
      <environment id="development">
        <transactionManager type="jdbc"/>
        <dataSource type="POOLED">
          <property name="driver" value="${driver}"/>
          <property name="url" value="${url}"/>
          <property name="username" value="${username}"/>
          <property name="password" value="${password}"/>
        </dataSource>
      </environment>
    </environments>
    <!-- 4.注册映射文件 -->
    <mappers>
      <mapper resource="com/mapper/ScottMapper.xml"/>
    </mappers>

 </configuration>

Configuration.xml

5.在src下com.entity包下创建Dept.java

 package com.entity;

 public class Dept {

     private int deptno;

     private String dname;

     public Dept() {
     }
     public Dept(int deptno, String dname) {
         this.deptno = deptno;
         this.dname = dname;
     }
     public int getDeptno() {
         return deptno;
     }
     public void setDeptno(int deptno) {
         this.deptno = deptno;
     }
     public String getDname() {
         return dname;
     }
     public void setDname(String dname) {
         this.dname = dname;
     }
     @Override
     public String toString() {
         return "Dept [deptno=" + deptno + ", dname=" + dname + "]";
     }

 }

Dept.java

6.在src下com.entity包下创建Emp.java

 package com.entity;

 public class Emp {
     private int empno; //员工编号
     private String ename; //员工姓名
     private double sal; //工资
     private Dept dept; //外键列：部门对象

     public Emp() {
     }
     public Emp(int empno, String ename, double sal, Dept dept) {
         this.empno = empno;
         this.ename = ename;
         this.sal = sal;
         this.dept = dept;
     }
     public int getEmpno() {
         return empno;
     }
     public void setEmpno(int empno) {
         this.empno = empno;
     }
     public String getEname() {
         return ename;
     }
     public void setEname(String ename) {
         this.ename = ename;
     }
     public double getSal() {
         return sal;
     }
     public void setSal(double sal) {
         this.sal = sal;
     }
     public Dept getDept() {
         return dept;
     }
     public void setDept(Dept dept) {
         this.dept = dept;
     }

 /*    @Override
     public String toString() {
         return "Emp [ empno=" + empno + ", ename=" + ename
                 + ", sal=" + sal + "]";
     }*/

 }

Emp.java

7.在src下com.util包下创建MyBatisUtil.java

 package com.util;

 import java.io.IOException;
 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;

 public class MyBatisUtil {
     private static SqlSessionFactory sqlSessionFactory=null;
     static{
         try {
             Reader reader=Resources.getResourceAsReader("Configuration.xml");
             sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

     public static SqlSession getSeqlsession(boolean isCommit){
         return sqlSessionFactory.openSession(isCommit);
     }

 }

MyBatisUtil.java

8.在src下com.mapper包下创建ScottMapper.java接口

 package com.mapper;

 import java.util.List;

 import com.entity.Dept;
 import com.entity.Emp;

 /**
  * 映射接口
  * @author pc
  *
  */
 public interface ScottMapper {
    /**
     * 1.查询员工表是延迟加载部门信息
     * @return
     */
    List<Emp> getEmpLazyLoading();

    /**
     * 2.根据部门编号查询某个部门信息
     * @param deptno
     * @return
     */
    Dept findByDeptno(int deptno);

 }

ScottMapper.java

9.在src下com.mapper包下创建ScottMapper.xml

 <?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.mapper.ScottMapper">
   <!-- 1.查询从表数据Emp -->
   <select id="getEmpLazyLoading" resultMap="EmpLazyLoading">
      select * from emp
   </select>

   <!-- 2.配置id=EmpLazyLoading的resultMap -->
   <resultMap id="EmpLazyLoading" type="Emp">
      <id property="empno" column="empno"/>
      <result property="ename" column="ename"/>
      <result property="sal" column="sal"/>

      <!-- 外键字段：多对一映射 -->
      <association property="dept" javaType="Dept" column="deptno" select="findByDeptno"/>
   </resultMap>

   <!-- 3.根据部门编号查询部门信息 -->
   <select id="findByDeptno" parameterType="int" resultType="Dept">
      select * from dept where deptno=#{deptno}
   </select>

 </mapper>

ScottMapper.xml

10.在src下com.mapper.impl包下创建ScottMapperImpl.java

 package com.mapper.impl;

 import java.util.List;

 import org.apache.ibatis.session.SqlSession;

 import com.entity.Dept;
 import com.entity.Emp;
 import com.mapper.ScottMapper;
 import com.util.MyBatisUtil;

 public class ScottMapperImpl implements ScottMapper {
     /**
      * 1.查询所有员工信息
      */
     public List<Emp> getEmpLazyLoading() {
         SqlSession sqlSession=MyBatisUtil.getSeqlsession(false);
         ScottMapper mapper=sqlSession.getMapper(ScottMapper.class);
         List<Emp> emp=mapper.getEmpLazyLoading();
         sqlSession.close();
         return emp;
     }
     /**
      * 2.根据部门编号查询部门信息
      */
     public Dept findByDeptno(int deptno) {
         SqlSession sqlSession=MyBatisUtil.getSeqlsession(false);
         ScottMapper mapper=sqlSession.getMapper(ScottMapper.class);
         List<Emp> emp=mapper.getEmpLazyLoading();
         Dept dept=mapper.findByDeptno(deptno);
         sqlSession.close();
         return dept;
     }

 }

ScottMapperImpl.java

11.在src下com.test包下创建Test.java

 package com.test;

 import java.util.List;

 import com.entity.Emp;
 import com.mapper.ScottMapper;
 import com.mapper.impl.ScottMapperImpl;

 public class Test {
     public static void main(String[] args) {
         ScottMapper mapper=new ScottMapperImpl();
         List<Emp> list=mapper.getEmpLazyLoading();
         for (Emp emp : list) {
             System.out.println(emp.getDept().getDname());
         }
         //System.out.println(mapper.findByDeptno(10));;
     }

 }

Test.java