摘要：一級緩存對于一級緩存來說是直接單個線程隔離的在執行的時候會自動清空緩存避免臟讀造成的影響此時為線程隔離的而管理對象為所有線程所共享的修改展示層獲取開始時間獲取結束時間查看日志可以看到只查

對于一級緩存來說,Mybatis是直接單個線程隔離的
在執行add,update,delete 的時候,會自動清空緩存,避免臟讀造成的影響
此時mapper為線程隔離的,而管理對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(); //獲取結束時間

%>

<%
    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SqlSession是相互隔離的

二級緩存直接添加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select語句將會緩存
insert update delete 將會刷新緩存
會使用LRU算法進行回收
根據時間表 緩存不會用任何時間順序來刷新緩存
緩存會存儲列表集合或對象 1024個引用

由于對象需要序列化所以需要實現 java.io.Serializable接口

父類實現序列化 子類會自動實現序列化 若子類實現序列化 父類沒有實現序列化 此時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,可以發現再次讀取的時候,直接從緩存中獲取了.
緩存生效,并為執行sql語句

已經命中緩存

這個需要實現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...暫時先不連接