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MyBatis 缓存
日期：2019-04-18点击：268收藏
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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