缓存技术（一）ssm添加缓存技术

梦里梦外; 2023-05-30 06:16 115阅读 0赞

# 学习指南： #

我们在写一般的项目在使用增删改查，一般是直接操作数据库，但是我们可以换一个思路，如果当前时间段1万个人同时访问数据库，就会造成数据库的宕机。我们可不可以换个思路，把数据库复制一份“一模一样”的数据，只要查一次就完成了复制，如果下次再进行查询，就直接从“副本”里进行查询。这样就不会直接访问数据库了。这种副本就叫做缓存。这个技术就叫做缓存技术。

## 基础项目三层结构： ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTgxMTU0_size_16_color_FFFFFF_t_70][]

## 添加缓存后的层次结构： ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTgxMTU0_size_16_color_FFFFFF_t_70 1][]

## **RedisTemplate对象介绍** ##

使用Spring提供的一个操作Redis数据库的模板对象，提供了对象redis数据库的增删查改的功能，封装了Jedis，同时自身实现了:

**对象的序列化和反序列化功能(obj----byte\[\]),作为对象存储的默认方案。**

**如果需要将对象转化为json字符串存储，需要覆盖默认方案。**

**RedisTemplate操作对象我们已经在之前以及有提及，所以这次直接上手项目：**

**第一步：导入pom依赖（和之前ssm整合的依赖无异，需要额外添加的是：jackson包、Jedis包、spring-data-redis包（封装了Jedis））**

<project xmlns="http://maven.apache.org/POM/4.0.0"
    	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    	<modelVersion>4.0.0</modelVersion>
    	<groupId>com.bjsxt.usercache</groupId>
    	<artifactId>maven-cache</artifactId>
    	<version>0.0.1-SNAPSHOT</version>
    	<packaging>war</packaging>
    
    	
    	<dependencies>
    		
    		<dependency>
    			<groupId>mysql</groupId>
    			<artifactId>mysql-connector-java</artifactId>
    			<version>5.1.38</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.mybatis</groupId>
    			<artifactId>mybatis</artifactId>
    			<version>3.4.6</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.mybatis</groupId>
    			<artifactId>mybatis-spring</artifactId>
    			<version>1.3.2</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>com.github.pagehelper</groupId>
    			<artifactId>pagehelper</artifactId>
    			<version>4.0.3</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>com.alibaba</groupId>
    			<artifactId>druid</artifactId>
    			<version>1.1.10</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-aop</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-beans</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-beans</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-context</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-core</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-expression</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-jdbc</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-tx</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-web</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>org.springframework</groupId>
    			<artifactId>spring-webmvc</artifactId>
    			<version>4.3.18.RELEASE</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>javax.servlet</groupId>
    			<artifactId>jstl</artifactId>
    			<version>1.2</version>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>javax.servlet.jsp</groupId>
    			<artifactId>jsp-api</artifactId>
    			<version>2.2</version>
    			<scope>provided</scope>
    		</dependency>
    
    		
    		<dependency>
    			<groupId>javax.servlet</groupId>
    			<artifactId>servlet-api</artifactId>
    			<version>2.5</version>
    			<scope>provided</scope>
    		</dependency>
    
    		<dependency>
    			<groupId>org.aspectj</groupId>
    			<artifactId>aspectjweaver</artifactId>
    			<version>1.9.4</version>
    		</dependency>
    		
    		
    		<dependency>
    			<groupId>com.fasterxml.jackson.core</groupId>
    			<artifactId>jackson-databind</artifactId>
    			<version>2.7.0</version>
    		</dependency>
    		
    		
    		<dependency>
    			<groupId>redis.clients</groupId>
    			<artifactId>jedis</artifactId>
    			<version>2.9.0</version>
    		</dependency>
    
    
    		
    		<dependency>
    			<groupId>org.springframework.data</groupId>
    			<artifactId>spring-data-redis</artifactId>
    			<version>1.8.6.RELEASE</version>
    		</dependency>
    	</dependencies>
    </project>

**第二步：书写一个正常的ssm项目：我们这里书写一个能够正常的查询，修改，删除的ssm简易项目：**

xml文件一：application-context.xml

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xsi:schemaLocation="                                               
                http://www.springframework.org/schema/beans    
                http://www.springframework.org/schema/beans/spring-beans.xsd    
              ">
    	
    	<bean id="dataSource"
    		class="com.alibaba.druid.pool.DruidDataSource">
    		<property name="driverClassName"
    			value="com.mysql.jdbc.Driver"></property>
    		<property name="url"
    			value="jdbc:mysql://localhost:3306/db_email"></property>
    		<property name="username" value="root"></property>
    		<property name="password" value="root"></property>
    	</bean>
    
    	
    	<bean id="sqlSessionFactory"
    		class="org.apache.ibatis.session.SqlSessionFactory">
    		
    		<property name="dataSource" ref="dataSource"></property>
    		
    		<property name="plugins">
    			<list>
    				
    				<bean class="com.github.pagehelper.PageHelper">
    					
    					<property name="properties">
    						<props>
    							
    							<prop key="dialect">mysql</prop>
    							
    							<prop key="reasonable">true</prop>
    						</props>
    					</property>
    				</bean>
    			</list>
    		</property>
    	</bean>
    
    	
    	<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    		<property name="basePackage" value="com.bjsxt.mapper"></property>
    		<property name="sqlSessionFactoryBeanName"
    			value="sqlSessionFactory"></property>
    	</bean>
    
    
    </beans>

**文件二：applicationContext-service.xml的配置**

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xmlns:aop="http://www.springframework.org/schema/aop"
    	xmlns:tx="http://www.springframework.org/schema/tx"
    	xmlns:context="http://www.springframework.org/schema/context"
    	xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop.xsd
           http://www.springframework.org/schema/tx
            http://www.springframework.org/schema/tx/spring-tx.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd">
            
    	
    	<context:component-scan base-package="com.bjsxt.service.impl"></context:component-scan>
    	
    	
    	<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    		<property name="dataSource" ref="dataSource"></property>
    	</bean>
    	
    	
    	<tx:advice id="txAdvice" transaction-manager="transactionManager">
    		<tx:attributes>
    			<tx:method name="load*" read-only="true"/>
    			<tx:method name="save*" read-only="false"/>
    			<tx:method name="insert*" read-only="false"/>
    			<tx:method name="delete*" read-only="false"/>
    			<tx:method name="update*" read-only="false"/>
    			<tx:method name="*" read-only="true"/>
    		</tx:attributes>
    	</tx:advice>
    	
    	<aop:config>
    		<aop:pointcut expression="execution(* com.bjsxt.service.impl.*.*(..))" id="pc"/>
    		<aop:advisor advice-ref="txAdvice" pointcut-ref="pc"/>
    	</aop:config>
    
    
    </beans>

**文件三：配置springmvc.xml文件**

**配置文件四：我们在这里还需要加入cache.xml文件配置，**

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xsi:schemaLocation="                                               
                http://www.springframework.org/schema/beans    
                http://www.springframework.org/schema/beans/spring-beans.xsd    
              ">
    
    	
    	<bean id="redisTemplate"
    		class="org.springframework.data.redis.core.RedisTemplate">
    		
    		<property name="connectionFactory" ref="connectionFactory"></property>
    		<property name="keySerializer" ref="keySerializer"></property>
    		<property name="valueSerializer" ref="valueSerializer"></property>
    	</bean>
    	
    	
    	<bean id="connectionFactory"
    		class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory">
    		<property name="hostName" value="192.168.224.11"></property>
    		<property name="port" value="6379"></property>
    	</bean>
    	
    	
    	<bean id="keySerializer" 
    		class="org.springframework.data.redis.serializer.StringRedisSerializer"></bean>
    
    	<bean id="valueSerializer" 
    		class="org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer"></bean>
    </beans>

**配置web.xml文件**

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
      <display-name>car2-controller</display-name>
      <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
      </welcome-file-list>
      
      <context-param>
      	<param-name>contextConfigLocation</param-name>
      	<param-value>classpath:applicationContext-*.xml</param-value>
      </context-param>
      
      <listener>
      	<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
      </listener>
      
      <servlet>
      	<servlet-name>springmvc</servlet-name>
      	<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
      	<init-param>
      		<param-name>contextConfigLocation</param-name>
      		<param-value>classpath:springmvc.xml</param-value>
      	</init-param>
      </servlet>
      <servlet-mapping>
      	<servlet-name>springmvc</servlet-name>
      	<url-pattern>/</url-pattern>
      </servlet-mapping>
      
      <filter>
      	<filter-name>charset</filter-name>
      	<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
      	<init-param>
      		<param-name>encoding</param-name>
      		<param-value>utf-8</param-value>
      	</init-param>
      </filter>
      <filter-mapping>
      	<filter-name>charset</filter-name>
      	<url-pattern>/*</url-pattern>
      </filter-mapping>
    </web-app>

### 关键部分：Service实现类 ###

缓存是从service实现类时查询缓存：

package com.bjsxt.service.impl;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.data.redis.core.BoundValueOperations;
    import org.springframework.data.redis.core.RedisTemplate;
    import org.springframework.stereotype.Service;
    
    import com.bjsxt.mapper.UserMapper;
    import com.bjsxt.pojo.User;
    import com.bjsxt.service.UserService;
    
    @Service
    public class UserServiceImpl implements UserService {
    	@Autowired
    	UserMapper userMapper;
    	
    	//加载redisTemplate对象
    	@Autowired
    	RedisTemplate<String, User>redisTemplate;
    	
    	@Override
    	public User selectUser(Integer uid) {
    		//通过redisTemplate绑定键
    		BoundValueOperations<String,User> boundValueOps = redisTemplate.boundValueOps(String.valueOf(uid));
    		//通过这个键取得相应的值(对象)
    		User user = boundValueOps.get();
    		//第一次查为空，之后查就一直会从缓存中读取数据
    		if(user!=null) {
    			return user;
    		}
    		//第一次查的情况会先从数据库查
    		user=userMapper.selectUser(uid);
    		//将查到的数据添加到Redis数据库中
    		boundValueOps.set(user);
    		return null;
    	}
    
    	@Override
    	public void updateUser(User user) {
    		BoundValueOperations<String,User> boundValueOps = redisTemplate.boundValueOps(String.valueOf(user.getUid()));
    		//对相同的键进行值的覆盖，也就是对象的覆盖达到更新的效果
    		boundValueOps.set(user);
    		//更新数据库操作
    		userMapper.updateUser(user);
    
    	}
    
    	@Override
    	public void deleteUser(Integer uid) {
    		//直接删除键为uid的这个对象
    		redisTemplate.delete(String.valueOf(uid));
    		userMapper.deleteUser(uid);
    
    	}
    
    }

**这样就可以通过缓存来进行查询了**

**总结：  需要修改pom中的依赖   （Jedis   spring-data-jedis    jackson）**

**             添加cache.xml注解。**

**              修改service实现类修改代码，其余地方不动**

## **二：使用注解来实现缓存机制：** ##

**与自己手写代码不同的是，**

**一：对cache.xml文件进行修改，添加注解驱动，以及注解管理**

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"        
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
        xmlns:cache="http://www.springframework.org/schema/cache" 
        xsi:schemaLocation="                                               
                http://www.springframework.org/schema/beans    
                http://www.springframework.org/schema/beans/spring-beans.xsd
                http://www.springframework.org/schema/cache    
                http://www.springframework.org/schema/cache/spring-cache.xsd  
              ">
              
        
         
         
         
         <bean id="connectionFactory" 
         	class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory">
         	<property name="hostName" value="192.168.25.100"></property>
         	<property name="port" value="6379"></property>
         	
         </bean>
         
         
         <bean id="keySerializer" 
         	class="org.springframework.data.redis.serializer.StringRedisSerializer"></bean>
             
         <bean id="valueSerializer" 
         	class="org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer">
         </bean> 
         
         <bean id="redisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
         	
         	<property name="connectionFactory" ref="connectionFactory"></property>
         	
         	<property name="keySerializer" ref="keySerializer"></property>
         	
         	<property name="valueSerializer" ref="valueSerializer"></property>
         </bean>
         
         
          
         <bean id="cacheManager" class="org.springframework.data.redis.cache.RedisCacheManager">
         	
         	<constructor-arg name="redisOperations" ref="redisTemplate"></constructor-arg>
         </bean>
             
         <cache:annotation-driven cache-manager="cacheManager"/>
         
         
         
    </beans>

**修改Service层的返回值（有注解是对方法的返回值进行缓存，所以更新不能再是无返回值的了。），在serviceImpl添加注解**

**这么做的优点是在不改动源代码的情况下就能够实现缓存机制。**

**实现类的代码：**

package com.bjsxt.service.impl;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.cache.annotation.CacheEvict;
    import org.springframework.cache.annotation.CachePut;
    import org.springframework.cache.annotation.Cacheable;
    import org.springframework.stereotype.Service;
    
    import com.bjsxt.mapper.UsersMapper;
    import com.bjsxt.pojo.Users;
    import com.bjsxt.service.UsersService;
    
    @Service
    public class UsersServiceImpl implements UsersService {
    
    	//注入Mapper
    	@Autowired
    	private UsersMapper usersMapper;
    	 
    	/***
    	 * @Cacheable() 作用，缓存方法的返回值,该方法在第一次查询的时候进入
    	 * cacheNames:给缓存起的名字
    	 * key:表示redis数据库的键
    	 */
    	@Cacheable(cacheNames= {"users_cahce"},key="#id+''")
    	@Override
    	public Users loadUsersService(Integer id) {
    		// TODO Auto-generated method stub
    		System.out.println("=======查询数据库========");
    		Users users= usersMapper.loadUsersMapper(id);
    		return users;
    	}
    
    	@CacheEvict(cacheNames= {"users_cahce"},key="#id+''")
    	@Override
    	public void deleteUsersService(Integer id) {
    		// TODO Auto-generated method stub
    		usersMapper.deleteUsersMapper(id);	
    	}
    
    	/***
    	 * @CachePut作用，缓存方法的返回值，每次都进入
    	 * cacheNames:给缓存起的名字
    	 * key:表示redis数据库的键
    	 * 	   可以使用spring的el表达式，主要是获得方法的参数值
    	 * 		如果是简单的数据类型String，Integer
    	 *      	只有一个参数：#p0  或者  #argName
    	 *      	只有一个参数：#p0,#p1  或者  #argName1,#argName2
    	 *      如果参数是javabean对象：
    	 *      	#javabean.属性名
    	 *      	
    	 */
    	@CachePut(cacheNames= {"users_cahce"},key="#users.id+''")
    	@Override
    	public Users updateUsersService(Users users) {
    		// TODO Auto-generated method stub
    		System.out.println("=======更新redis缓存======");
    		usersMapper.updateUsersMapper(users);
    		
    		return users;
    	}
    
    }

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