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 Connection2019-04-17 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: 12019-04-17 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]: 0.75862068965517242019-04-18 00:55:44.430 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.76666666666666672019-04-18 00:55:44.433 [DEBUG] org.apache.ibatis.cache.decorators.LoggingCache.getObject(LoggingCache.java:62) - Cache Hit Ratio [com.ming.MyBatis.RoleMapper]: 0.77419354838709682019-04-18 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