MyBatis 缓存

一级缓存

对于一级缓存来说,Mybatis是直接单个线程隔离的

在执行add,update,delete 的时候,会自动清空缓存,避免脏读造成的影响

此时mapper为线程隔离的,而管理对象为所有线程所共享的.

修改展示层

<%@ page import="org.apache.ibatis.session.SqlSession" %>
<%@ page import="com.ming.Util.SqlSessionFactoryUtil" %>
<%@ page import="com.ming.MyBatis.RoleMapper" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.Iterator" %>
<%@ page import="com.ming.MyBatis.POJO.Student" %>
<html>
<body>
<h2>Hello World!</h2>

<%
    long startTime = System.currentTimeMillis(); //获取开始时间
    SqlSession sqlSession = null;
    List<Student> students = null;
    List<Student> students1 = null;
        try {
            sqlSession = SqlSessionFactoryUtil.openSqlSesion();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            students = roleMapper.getStudent(1);
            students1 = roleMapper.getStudent(1);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
    }
    long endTime = System.currentTimeMillis(); //获取结束时间

%>

<%
    Iterator iterator = students.iterator();
    while(iterator.hasNext()){
        %>
            <%=((Student)iterator.next()).getGender()%>

        <%
    }
    iterator = students1.iterator();
    while(iterator.hasNext()){
        %>
            <%=((Student)iterator.next()).getGender()%>
        <%
    }
%>
</body>
</html>

查看日志

2019-04-17 22:33:38.147 [DEBUG] org.apache.ibatis.transaction.jdbc.JdbcTransaction.openConnection(JdbcTransaction.java:136) - Opening JDBC Connection
2019-04-17 22:33:38.147 [DEBUG] org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:397) - Checked out connection 879027360 from pool.
2019-04-17 22:33:38.148 [DEBUG] org.apache.ibatis.transaction.jdbc.JdbcTransaction.setDesiredAutoCommit(JdbcTransaction.java:100) - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@3464e4a0]
2019-04-17 22:33:38.161 [DEBUG] org.apache.ibatis.logging.jdbc.BaseJdbcLogger.debug(BaseJdbcLogger.java:143) - ==>  Preparing: SELECT student.uid, student.gender, student.remarks, student.student_id_number, student.student_name FROM student WHERE student.uid = 1; 
2019-04-17 22:33:38.162 [DEBUG] org.apache.ibatis.logging.jdbc.BaseJdbcLogger.debug(BaseJdbcLogger.java:143) - ==> Parameters: 
2019-04-17 22:33:38.181 [DEBUG] org.apache.ibatis.logging.jdbc.BaseJdbcLogger.debug(BaseJdbcLogger.java:143) - <==      Total: 1
2019-04-17 22:33:38.183 [DEBUG] org.apache.ibatis.transaction.jdbc.JdbcTransaction.resetAutoCommit(JdbcTransaction.java:122) - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@3464e4a0]
2019-04-17 22:33:38.200 [DEBUG] org.apache.ibatis.transaction.jdbc.JdbcTransaction.close(JdbcTransaction.java:90) - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@3464e4a0]
2019-04-17 22:33:38.201 [DEBUG] org.apache.ibatis.datasource.pooled.PooledDataSource.pushConnection(PooledDataSource.java:362) - Returned connection 879027360 to pool.

可以看到只查询了一次

需要注意的是缓存在各个SqlSession是相互隔离的

二级缓存

二级缓存直接添加cache即可

<?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">
<!-- 定义接口类 -->
<mapper namespace="com.ming.MyBatis.RoleMapper">
	
	<resultMap type="role" id="roleMap">
		<!-- id为主键映射关系 其中数据库中的id为主键 -->
		<id column="id" property="id" javaType="int" jdbcType="INTEGER"/>
		<!-- result为其他基本数据类型和实体类之间的映射 映射关系为role_name 到 roleName之间的映射 数据类型为string到VARCHAR之间的映射关系 -->
		<result column="role_name" property="roleName" javaType="string" jdbcType="VARCHAR"/>
		<!-- 这里使用typeHandler表示遇到此处理集的时候,将会执行com.ming.MyBatis.StringTypeHandler -->
		<result column="note" property="note" typeHandler="com.ming.MyBatis.StringTypeHandler"/>
	</resultMap>
	
	<select id="getRole" parameterType="int" resultType="com.ming.MyBatis.POJO.Role">
		SELECT id, role_name as roleName, note FROM t_role WHERE id = #{id}
	</select>
	
	<select id="findRoleByteMap" parameterType="map" resultMap="roleMap">
		SELECT id, role_name, note FROM t_role
		WHERE role_name LIKE CONCAT('%', #{roleName}, '%')
		AND note LIKE CONCAT('%', #{note}, '%')
	</select>
	
	<select id="findRoleByteMap1" resultMap="roleMap">
		SELECT id, role_name, note FROM t_role
		WHERE role_name LIKE CONCAT('%', #{roleName}, '%')
		AND note LIKE CONCAT('%', #{note}, '%')
	</select>
	
	
	<resultMap id="studentSelfCardMap" type="com.ming.MyBatis.POJO.StudentCard">
		<id column="uid" property="uid"/>
		<result column="student_number" property="studentNumber"/>
		<result column="birthplace" property="birthplace" />
		<result column="date_of_issue" property="dateOfIssue" jdbcType="DATE" javaType="java.util.Date"/>
		<result column="end_date" property="endDate" jdbcType="DATE" javaType="java.util.Date"/>
		<result column="remarks" property="remarks" />
	</resultMap>

	<select id="findStudentSelfCardByStudentId" parameterType="int" resultMap="studentSelfCardMap">
		SELECT student_card.uid, student_card.student_number, student_card.remarks,
		student_card.end_date, student_card.date_of_issue, student_card.birthplace
		FROM student_card WHERE student_card.uid = #{studentId};
	</select>
	
	<resultMap id="studentMap" type="com.ming.MyBatis.POJO.Student">
		<id column="uid" property="uid"/>
		<result column="student_name" property="studentName"/>
		<result column="gender" property="gender"/>
		<result column="student_id_number" property="studentIdNumber"/>
		<result column="remarks" property="remarks"/>
		<!--将会调用接口代表的SQL 进行执行查询 -->
		<association property="studentCard" column="uid" select="com.ming.MyBatis.RoleMapper.findStudentSelfCardByStudentId"/>
	</resultMap>
	
	<select id="getStudent" parameterType="int" resultMap="studentMap">
		SELECT student.uid, student.gender, student.remarks, student.student_id_number,
		student.student_name
		FROM student
		WHERE student.uid = 1;
	</select>
	
	<cache/>
</mapper>

此时select语句将会缓存

insert update delete 将会刷新缓存

会使用LRU算法进行回收

根据时间表 缓存不会用任何时间顺序来刷新缓存

缓存会存储列表集合或对象 1024个引用

由于对象需要序列化所以需要实现 java.io.Serializable接口

父类实现序列化 子类会自动实现序列化 若子类实现序列化 父类没有实现序列化 此时在子类中保存父类的值,直接跳过2019-04-18 00:55:44.428 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.7586206896551724 2019-04-18 00:55:44.430 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.7666666666666667 2019-04-18 00:55:44.433 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.7741935483870968 2019-04-18 00:55:44.435 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.78125查看日志,可以发现再次读取的时候,直接从缓存中获取了.

缓存生效,并为执行sql语句

已经命中缓存

自定义缓存

这个需要实现cache接口

package com.ming.MyBatis;

import java.util.concurrent.locks.ReadWriteLock;

/**
 * @author ming
 */
public class Cache implements org.apache.ibatis.cache.Cache {
    /**
     * @return The identifier of this cache
     */
    @Override
    public String getId() {
        return null;
    }

    /**
     * @param key   Can be any object but usually it is a {@link CacheKey}
     * @param value The result of a select.
     */
    @Override
    public void putObject(Object key, Object value) {

    }

    /**
     * @param key The key
     * @return The object stored in the cache.
     */
    @Override
    public Object getObject(Object key) {
        return null;
    }

    /**
     * As of 3.3.0 this method is only called during a rollback
     * for any previous value that was missing in the cache.
     * This lets any blocking cache to release the lock that
     * may have previously put on the key.
     * A blocking cache puts a lock when a value is null
     * and releases it when the value is back again.
     * This way other threads will wait for the value to be
     * available instead of hitting the database.
     *
     * @param key The key
     * @return Not used
     */
    @Override
    public Object removeObject(Object key) {
        return null;
    }

    /**
     * Clears this cache instance.
     */
    @Override
    public void clear() {

    }

    /**
     * Optional. This method is not called by the core.
     *
     * @return The number of elements stored in the cache (not its capacity).
     */
    @Override
    public int getSize() {
        return 0;
    }

    /**
     * Optional. As of 3.2.6 this method is no longer called by the core.
     * <p>
     * Any locking needed by the cache must be provided internally by the cache provider.
     *
     * @return A ReadWriteLock
     */
    @Override
    public ReadWriteLock getReadWriteLock() {
        return null;
    }
}

然后redis直接操作即可

额...暂时先不连接

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