MyBatis 缓存

摘要：一级缓存对于一级缓存来说是直接单个线程隔离的在执行的时候会自动清空缓存避免脏读造成的影响此时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获取开始时间获取结束时间查看日志可以看到只查

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" %>


Hello World!

<%
    long startTime = System.currentTimeMillis(); //获取开始时间
    SqlSession sqlSession = null;
    List students = null;
    List 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()%>
        <%
    }
%>

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

二级缓存直接添加cache即可

    
    
        
        
        
        
        
        
    
    
    
        SELECT id, role_name as roleName, note FROM t_role WHERE id = #{id}
    
    
    
        SELECT id, role_name, note FROM t_role
        WHERE role_name LIKE CONCAT("%", #{roleName}, "%")
        AND note LIKE CONCAT("%", #{note}, "%")
    
    
    
        SELECT id, role_name, note FROM t_role
        WHERE role_name LIKE CONCAT("%", #{roleName}, "%")
        AND note LIKE CONCAT("%", #{note}, "%")
    
    
    
    
        
        
        
        
        
        
    

    
        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 student.uid, student.gender, student.remarks, student.student_id_number,
        student.student_name
        FROM student
        WHERE student.uid = 1;
    
    
    

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

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.
     * 

     * 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