6.1 MyBatis_缓存及MyBatis整合ehcache

系统管理员 2022-05-31 09:07 201阅读 0赞

1.目录结构

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导入必要的jar包并使用mysql数据库创建表

2.代码

Employee.java

package com.bean;
    
    import java.io.Serializable;
    
    public class Employee implements Serializable{
    	private Integer id;
    	private String lastName;
    	private String email;
    	private String gender;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public String getLastName() {
    		return lastName;
    	}
    	public void setLastName(String lastName) {
    		this.lastName = lastName;
    	}
    	public String getEmail() {
    		return email;
    	}
    	public void setEmail(String email) {
    		this.email = email;
    	}
    	public String getGender() {
    		return gender;
    	}
    	public void setGender(String gender) {
    		this.gender = gender;
    	}
    	
    	public Employee(Integer id, String lastName, String email, String gender) {
    		super();
    		this.id = id;
    		this.lastName = lastName;
    		this.email = email;
    		this.gender = gender;
    	}
    	public Employee() {};
    	
    	@Override
    	public String toString() {
    		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
    	}
    
    	
    
    }

EmployeeMapper.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.dao.EmployeeMapper">
     
     	<cache type="org.mybatis.caches.ehcache.EhcacheCache"><property name="employee" value=""/></cache>
     	
     	
     	
     	
     	    
      
     	 
       
    	<sql id="insertColumn">
    		<if test="_databaseId=='mysql'">
    			id,last_name,email,gender
    		</if>
    		<if test="_databaseId=='oracle'">
    			id,last_name,email,department_id
    		</if>
    	</sql>
    	
    	<insert id="addEmployeeBysql" databaseId="mysql">
    		insert into tbl_employee(
    			
    			<include refid="insertColumn" ></include>
    		) 
    		values (#{id},#{lastName},#{email},#{gender})
    	</insert>
    	
    	<select id="getEmployeeById" resultType="com.bean.Employee" databaseId="mysql" 
    		useCache="true" >
    		select * from tbl_employee where id=#{id}
    	</select>
       		 
    </mapper>

EmployeeMapper.java

package com.dao;
    
    import java.util.List;
    
    import org.apache.ibatis.annotations.Param;
    
    import com.bean.Employee;
    
    public interface EmployeeMapper {
    	
    	
    	//11.测试sql可重复片段
    	public void addEmployeeBysql(Employee employee);
    	
    	//测试缓存cache
    	public Employee getEmployeeById(Integer id);
    }

testMybatis.java

package com.test;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    import java.io.IOException;
    import java.io.InputStream;
    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 org.junit.Test;
    import com.bean.Employee;
    import com.dao.EmployeeMapper;
    
    public class testMybatis{
    	
    	private SqlSessionFactory getSqlSessionFactory() throws IOException {
    		String resource = "mybatis-config.xml";
    		InputStream inputStream = Resources.getResourceAsStream(resource);
    		SqlSessionFactory SqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
    		return SqlSessionFactory;
    	}
    	
    	@Test
    	public void testSQL() throws IOException {
    		SqlSessionFactory ssf=getSqlSessionFactory();
    		SqlSession ss=ssf.openSession();
    		try {
    			EmployeeMapper mapper=ss.getMapper(EmployeeMapper.class);
    			
    			Employee emp1=mapper.getEmployeeById(38);
    			System.out.println(emp1);
    			
    		/* 一级缓存失效的四种情况:
    		 * 1.SqlSession不同，Cache会失效
    			SqlSession ss2=ssf.openSession();
    			EmployeeMapper mapper2=ss2.getMapper(EmployeeMapper.class);
    			
    			Employee emp2=mapper2.getEmployeeById(38);
    			System.out.println(emp2);*/
    			
    		/*2.sqlSession相同，查询条件相同，但两次查询之间执行了增删改操作
    			mapper.addEmployeeBysql(new Employee(null,"yiwen","yiwen@qq.com","1"));*/
    			
    		/*3.SqlSession相同，查询条件不同
    			Employee emp3=mapper.getEmployeeById(41);
    			System.out.println(emp3);*/
    			
    		/*4.sqlSession相同，查询条件相同，手动清除了缓存clearCache()
    			ss.clearCache();*/
    			
    			Employee emp2=mapper.getEmployeeById(38);
    			System.out.println(emp2);
    			
    			System.out.println(emp1==emp2);
    			
    			ss.commit();
    		}
    		finally {
    			ss.close();
    			}	
    	
    	}
    	 
    	/* 二级缓存：基于namespace级别的缓存，一个namespace对应一个二级缓存
                   工作机制：
             1、一个会话查询一个数据，这个数据会被保存到当前会话的一级缓存中      
             2、如果会话关闭，一级缓存中的数据会被保存到二级缓存中，新的会话消息，就可以查询二级缓存
             3、不同namespace查出来的数据，会被放在自己对应的缓存中
    	 
    	 使用二级缓存的步骤：
    		第一步：开启缓存
    			在全局配置文件中开启缓存
    			<setting name="cacheEnabled" value="true"></setting>
    		第二步:在映射文件中配置缓存
    			<cache></cache>
    		第三步:pojo需要使用序列化接口
    		
    	和缓存有关的设置/属性：
    		1.cacheEnabled=true;false:关闭缓存（二级缓存关闭（一级缓存一直可用））
    		2.每个select标签都有useCache="true"
    			false:不使用缓存（一级缓存依然使用，二级缓存不适用）
    		3.每个增删改标签的：flushCache="true";（一级、二级缓存都会清除）
    			增删改执行完成后就会清除缓存
    			测试：flushCache="true":一级缓存就清空了，二级缓存也会被清除；
    			查询标签：fulshCache="false";
    				如果fulshCache="true";每次查询之后都会清空缓存，缓存是没有被使用的
    		4.SqlSession.cleanCache（）；只是清除当前Session的一级缓存
    		5.localCacheScope:本地缓存作用域：=SESSION（一级缓存SESSION）:当前回话的所有数据保存在回话缓存中。
    				=STATEMENT:可以禁用一级缓存	
    	*/
    	
    	/*第三方缓存整合：
    		1.导入第三方缓存包即可；
    		2.导入与第三方缓存整合的适配包；官方有下载（与spring整合的包，与hibernate整合的包）；
    		3.mapper.xmm中使用自定义缓存
    			<cache type="org.mybatis.caches.ehcache.EhcacheCache"></cache>
    		4.配置ehcache.xml*/
    	
    	@Test
    	public void cahetest() throws IOException {
    		SqlSessionFactory ssf=getSqlSessionFactory();
    		SqlSession ss2=ssf.openSession();
    		EmployeeMapper mapper2=ss2.getMapper(EmployeeMapper.class);
    		SqlSession ss3=ssf.openSession();
    		EmployeeMapper mapper3=ss3.getMapper(EmployeeMapper.class);
    		
    		Employee emp2=mapper2.getEmployeeById(42);
    		System.out.println(emp2);
    		ss2.close();//如果会话关闭，一级缓存中的数据会被保存到二级缓存中，新的会话消息，就可以查询二级缓存
    		
    		mapper3.addEmployeeBysql(new Employee(null,"songping","song@qq.com","1"));
    		ss3.commit();
    		
    		Employee emp3=mapper3.getEmployeeById(42);
    		System.out.println(emp3);
    		ss3.close();
    		
    			
    	}
    
    }

mybatis-config.xml

<?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>
    
    	
    	
    	<settings> 
            <setting name="logImpl" value="STDOUT_LOGGING"/>  
            <setting name="mapUnderscoreToCamelCase" value="true"/>
            <setting name="cacheEnabled" value="true"></setting>
        </settings> 
        
      <environments default="dev_mysql"  >
        <environment id="dev_mysql">
          <transactionManager type="JDBC"/>
          <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/mybatis?allowMultiQueries=true"/>
            <property name="username" value="root"/>
            <property name="password" value="shapolang"/>
          </dataSource>
        </environment>
        
         <environment id="dev_oracle">
        	<transactionManager type="JDBC"></transactionManager>
        	<dataSource type="POOLED">
    			<property name="driver" value="${oracle.driver}"></property>
    			<property name="url" value="${oracle.url}"></property>
    			<property name="username" value="${oracle.username" ></property>
    			<property name="password" value="${oracle.password}"></property>
        	</dataSource>
        </environment>
      </environments>
      
      
      <databaseIdProvider type="DB_VENDOR">
      	<property name="MySQL" value="mysql"/>
      	<property name="Oracle" value="oracle"/>
      	<property name="SQL Server" value="sqlserver"/>
      </databaseIdProvider>
      
      
      
      <mappers>
        <mapper resource="com/bean/EmployeeMapper.xml"/>
      </mappers>
    </configuration>

整合ehcache需要的配置文件ehcache.xml

<?xml version="1.0" encoding="UTF-8"?>
    <ehcache>
        <diskStore path="F:/ehcache/"></diskStore>
        
        
        <defaultCache
            maxElementsInMemory="10000"
            eternal="false"
            timeToIdleSeconds="120"
            timeToLiveSeconds="120"
            overflowToDisk="true"
        />
        
        
        <cache 
            name="employee" 
            maxElementsInMemory="10000" 
            eternal="false"
            timeToIdleSeconds="300" 
            timeToLiveSeconds="600" 
            overflowToDisk="true" 
        /> 
    
    </ehcache>

3.mybatis缓存原理图

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[Center]: /images/20220531/3160bb7243e848d7a66b22eebc180e34.png
[Center 1]: /images/20220531/213d314df88243569b3d3fcb263b9d72.png