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

 1 log4j.rootLogger=DEBUG, Console  
 2   
 3 #Console  
 4 log4j.appender.Console=org.apache.log4j.ConsoleAppender  
 5 log4j.appender.Console.layout=org.apache.log4j.PatternLayout  
 6 log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n  
 7   
 8 log4j.logger.java.sql.ResultSet=INFO  
 9 log4j.logger.org.apache=INFO  
10 log4j.logger.java.sql.Connection=DEBUG  
11 log4j.logger.java.sql.Statement=DEBUG  
12 log4j.logger.java.sql.PreparedStatement=DEBUG

log4j.properties

3.在src下创建jdbc.properties数据库属性文件

1 driver=oracle.jdbc.driver.OracleDriver
2 url=jdbc:oracle:thin:@127.0.0.1:1521:orcl
3 username=scott
4 password=tiger

jdbc.properties

4.在src下创建Configuration.xml主配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd" >
 3 <configuration>
 4    <!-- 1.jdbc链接数据库的主配置文件 -->
 5    <properties resource="jdbc.properties"/>
 6    
 7    <!-- 2.全局参数配置 -->
 8    <settings>
 9         <!--打开延迟加载的开关  -->
10         <setting name="lazyLoadingEnabled" value="true"/>
11          <!--将积极加载改为消极加载及按需加载  -->
12         <setting name="aggressiveLazyLoading" value="false"/>
13    </settings>
14    
15    <!-- 别名配置 -->
16    <typeAliases>
17      <typeAlias type="com.entity.Dept" alias="Dept"/>
18      <typeAlias type="com.entity.Emp" alias="Emp"/>
19    </typeAliases>
20    
21    <!-- 3.数据源的配置 -->
22    <environments default="development">
23      <environment id="development">
24        <transactionManager type="jdbc"/>
25        <dataSource type="POOLED">
26          <property name="driver" value="${driver}"/>
27          <property name="url" value="${url}"/>
28          <property name="username" value="${username}"/>
29          <property name="password" value="${password}"/>
30        </dataSource>
31      </environment>
32    </environments>
33    <!-- 4.注册映射文件 -->
34    <mappers>
35      <mapper resource="com/mapper/ScottMapper.xml"/>
36    </mappers>
37    
38 </configuration>

Configuration.xml

5.在src下com.entity包下创建Dept.java

 1 package com.entity;
 2 
 3 public class Dept {
 4     
 5     private int deptno;
 6     
 7     private String dname;
 8     
 9     public Dept() {
10     }
11     public Dept(int deptno, String dname) {
12         this.deptno = deptno;
13         this.dname = dname;
14     }
15     public int getDeptno() {
16         return deptno;
17     }
18     public void setDeptno(int deptno) {
19         this.deptno = deptno;
20     }
21     public String getDname() {
22         return dname;
23     }
24     public void setDname(String dname) {
25         this.dname = dname;
26     }
27     @Override
28     public String toString() {
29         return "Dept [deptno=" + deptno + ", dname=" + dname + "]";
30     }
31     
32 
33 }

Dept.java

6.在src下com.entity包下创建Emp.java

 1 package com.entity;
 2 
 3 public class Emp {
 4     private int empno; //员工编号
 5     private String ename; //员工姓名
 6     private double sal; //工资
 7     private Dept dept; //外键列：部门对象
 8     
 9     
10     public Emp() {
11     }
12     public Emp(int empno, String ename, double sal, Dept dept) {
13         this.empno = empno;
14         this.ename = ename;
15         this.sal = sal;
16         this.dept = dept;
17     }
18     public int getEmpno() {
19         return empno;
20     }
21     public void setEmpno(int empno) {
22         this.empno = empno;
23     }
24     public String getEname() {
25         return ename;
26     }
27     public void setEname(String ename) {
28         this.ename = ename;
29     }
30     public double getSal() {
31         return sal;
32     }
33     public void setSal(double sal) {
34         this.sal = sal;
35     }
36     public Dept getDept() {
37         return dept;
38     }
39     public void setDept(Dept dept) {
40         this.dept = dept;
41     }
42     
43 /*    @Override
44     public String toString() {
45         return "Emp [ empno=" + empno + ", ename=" + ename
46                 + ", sal=" + sal + "]";
47     }*/
48     
49     
50 
51 }

Emp.java

7.在src下com.util包下创建MyBatisUtil.java

 1 package com.util;
 2 
 3 import java.io.IOException;
 4 import java.io.Reader;
 5 
 6 import org.apache.ibatis.io.Resources;
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 public class MyBatisUtil {
12     private static SqlSessionFactory sqlSessionFactory=null;
13     static{
14         try {
15             Reader reader=Resources.getResourceAsReader("Configuration.xml");
16             sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
17         } catch (IOException e) {
18             e.printStackTrace();
19         }
20     }
21     
22     public static SqlSession getSeqlsession(boolean isCommit){
23         return sqlSessionFactory.openSession(isCommit);
24     }
25 
26 }

MyBatisUtil.java

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

 1 package com.mapper;
 2 
 3 import java.util.List;
 4 
 5 import com.entity.Dept;
 6 import com.entity.Emp;
 7 
 8 /**
 9  * 映射接口
10  * @author pc
11  *
12  */
13 public interface ScottMapper {
14    /**
15     * 1.查询员工表是延迟加载部门信息    
16     * @return
17     */
18    List<Emp> getEmpLazyLoading();
19    
20    /**
21     * 2.根据部门编号查询某个部门信息
22     * @param deptno
23     * @return
24     */
25    Dept findByDeptno(int deptno);
26    
27     
28 }

ScottMapper.java

9.在src下com.mapper包下创建ScottMapper.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
 3 <mapper namespace="com.mapper.ScottMapper">
 4   <!-- 1.查询从表数据Emp -->
 5   <select id="getEmpLazyLoading" resultMap="EmpLazyLoading">
 6      select * from emp
 7   </select>
 8   
 9   <!-- 2.配置id=EmpLazyLoading的resultMap -->
10   <resultMap id="EmpLazyLoading" type="Emp">
11      <id property="empno" column="empno"/>
12      <result property="ename" column="ename"/>
13      <result property="sal" column="sal"/>
14      
15      <!-- 外键字段：多对一映射 -->
16      <association property="dept" javaType="Dept" column="deptno" select="findByDeptno"/>
17   </resultMap>
18   
19   <!-- 3.根据部门编号查询部门信息 -->
20   <select id="findByDeptno" parameterType="int" resultType="Dept">
21      select * from dept where deptno=#{deptno}
22   </select>
23   
24 </mapper>

ScottMapper.xml

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

 1 package com.mapper.impl;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.session.SqlSession;
 6 
 7 import com.entity.Dept;
 8 import com.entity.Emp;
 9 import com.mapper.ScottMapper;
10 import com.util.MyBatisUtil;
11 
12 public class ScottMapperImpl implements ScottMapper {
13     /**
14      * 1.查询所有员工信息
15      */
16     public List<Emp> getEmpLazyLoading() {
17         SqlSession sqlSession=MyBatisUtil.getSeqlsession(false);
18         ScottMapper mapper=sqlSession.getMapper(ScottMapper.class);
19         List<Emp> emp=mapper.getEmpLazyLoading();
20         sqlSession.close();
21         return emp;
22     }
23     /**
24      * 2.根据部门编号查询部门信息
25      */
26     public Dept findByDeptno(int deptno) {
27         SqlSession sqlSession=MyBatisUtil.getSeqlsession(false);
28         ScottMapper mapper=sqlSession.getMapper(ScottMapper.class);
29         List<Emp> emp=mapper.getEmpLazyLoading();
30         Dept dept=mapper.findByDeptno(deptno);
31         sqlSession.close();
32         return dept;
33     }
34 
35 
36 }

ScottMapperImpl.java

11.在src下com.test包下创建Test.java

 1 package com.test;
 2 
 3 import java.util.List;
 4 
 5 import com.entity.Emp;
 6 import com.mapper.ScottMapper;
 7 import com.mapper.impl.ScottMapperImpl;
 8 
 9 public class Test {
10     public static void main(String[] args) {
11         ScottMapper mapper=new ScottMapperImpl();
12         List<Emp> list=mapper.getEmpLazyLoading();
13         for (Emp emp : list) {
14             System.out.println(emp.getDept().getDname());
15         }
16         //System.out.println(mapper.findByDeptno(10));;
17     }
18 
19 }

Test.java

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原文地址：https://www.cnblogs.com/holly8/p/5805079.html