摘要：一級(jí)緩存對(duì)于一級(jí)緩存來說是直接單個(gè)線程隔離的在執(zhí)行的時(shí)候會(huì)自動(dòng)清空緩存避免臟讀造成的影響此時(shí)為線程隔離的而管理對(duì)象為所有線程所共享的修改展示層獲取開始時(shí)間獲取結(jié)束時(shí)間查看日志可以看到只查

對(duì)于一級(jí)緩存來說,Mybatis是直接單個(gè)線程隔離的
在執(zhí)行add,update,delete 的時(shí)候,會(huì)自動(dòng)清空緩存,避免臟讀造成的影響
此時(shí)mapper為線程隔離的,而管理對(duì)象為所有線程所共享的.

修改展示層

<%@ 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(); //獲取開始時(shí)間
    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(); //獲取結(jié)束時(shí)間

%>

<%
    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.

可以看到只查詢了一次

需要注意的是緩存在各個(gè)SqlSession是相互隔離的

二級(jí)緩存直接添加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;
    
    
    

此時(shí)select語句將會(huì)緩存
insert update delete 將會(huì)刷新緩存
會(huì)使用LRU算法進(jìn)行回收
根據(jù)時(shí)間表 緩存不會(huì)用任何時(shí)間順序來刷新緩存
緩存會(huì)存儲(chǔ)列表集合或?qū)ο?1024個(gè)引用

由于對(duì)象需要序列化所以需要實(shí)現(xiàn) java.io.Serializable接口

父類實(shí)現(xiàn)序列化 子類會(huì)自動(dòng)實(shí)現(xiàn)序列化 若子類實(shí)現(xiàn)序列化 父類沒有實(shí)現(xiàn)序列化 此時(shí)在子類中保存父類的值,直接跳過

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,可以發(fā)現(xiàn)再次讀取的時(shí)候,直接從緩存中獲取了.
緩存生效,并為執(zhí)行sql語句

已經(jīng)命中緩存

這個(gè)需要實(shí)現(xiàn)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

額...暫時(shí)先不連接