Spring Boot 集成mybatis 用Redis做二级缓存

Love The Way You Lie 2022-05-03 08:58 507阅读 0赞

### 一：集成druid数据源 ###

一：导包

<dependency>
    			<groupId>com.alibaba</groupId>
    			<artifactId>druid</artifactId>
    			<version>1.1.10</version>
    		</dependency>

二：配置

用的是druid的连接池，jpa的自动建表，mytabis框架

spring:
      datasource:
        type: com.alibaba.druid.pool.DruidDataSource
        driver-class-name: com.mysql.jdbc.Driver
        url: jdbc:mysql://localhost:3306/springboot
        username: root
        password: root
        
      jpa:
        hibernate:
          ddl-auto: update
        show-sql: true
        
    mybatis:
      type-aliases-package: com.tom.bean
      mapper-locations: classpth:mapper/*mapper.xml

druid的额外配置

# 初始化大小，最小，最大
    spring.datasource.initialSize=5
    spring.datasource.minIdle=5
    spring.datasource.maxActive=20
    # 配置获取连接等待超时的时间
    spring.datasource.maxWait=60000
    # 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒
    spring.datasource.timeBetweenEvictionRunsMillis=60000
    # 配置一个连接在池中最小生存的时间，单位是毫秒
    spring.datasource.minEvictableIdleTimeMillis=300000
    # 校验SQL，Oracle配置 spring.datasource.validationQuery=SELECT 1 FROM DUAL，如果不配validationQuery项，则下面三项配置无用
    spring.datasource.validationQuery=SELECT 'x'
    spring.datasource.testWhileIdle=true
    spring.datasource.testOnBorrow=false
    spring.datasource.testOnReturn=false
    # 打开PSCache，并且指定每个连接上PSCache的大小
    spring.datasource.poolPreparedStatements=true
    spring.datasource.maxPoolPreparedStatementPerConnectionSize=20
    # 配置监控统计拦截的filters，去掉后监控界面sql无法统计，'wall'用于防火墙
    spring.datasource.filters=stat,wall,log4j
    # 通过connectProperties属性来打开mergeSql功能；慢SQL记录
    spring.datasource.connectionProperties=druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000
    # 合并多个DruidDataSource的监控数据
    spring.datasource.useGlobalDataSourceStat=true

三：Mapper，Service，Controller

bean，用的自动建表

@Entity
    public class teacher implements Serializable{
    	@Id
    	@GeneratedValue(strategy=GenerationType.IDENTITY)
    	private int id;
    	private String name;
    	private int age;
            ...
    }

mapper，暂时只写两个方法

@Mapper
    public interface teachMapper {
    	@Insert("insert into teacher values(null,#{age},#{name})") 
    	public void save(teacher t);
    	@Select("select * from teacher where id=#{id}")
    	public teacher getById(int id);
    	
    }

service

@Service
    public class teachService {
    	@Autowired
    	private teachMapper tm;
    
    	public teacher getById(int id) {
    		return tm.getById(id);
    	}
    	
    	public void save(teacher t) {
    		tm.save(t);
    	}
    }

Controller

@RestController
    @RequestMapping("/teacher")
    public class teachController {
    	@Autowired
    	private teachService ts;
    
    	@GetMapping("/{id}")
    	public teacher get(@PathVariable("id") int id) {
    		return ts.getById(id);
    	}
    	@PostMapping("/save")
    	public String save(teacher t) {
    		ts.save(t);
    		return "保存成功";
    	}
    }

四：druid配置

用druid的原因：一个因为听说它性能很强，另一个主要的原因为可以进行实时监控

@WebFilter(filterName="druidWebStatFilter",urlPatterns="/*",
    initParams={
        @WebInitParam(name="exclusions",value="*.js,*.gif,*.jpg,*.bmp,*.png,*.css,*.ico,/druid/*")// 忽略资源
    })
    public class DruidStatFilter extends WebStatFilter {
    
    }

@SuppressWarnings("serial")
    @WebServlet(urlPatterns = "/druid/*", 
    
    		initParams = { @WebInitParam(name = "allow", value = "127.0.0.1"), // IP白名单
    		@WebInitParam(name = "deny", value = "192.168.0.0"), // IP黑名单 (存在共同时，deny优先于allow)
    		@WebInitParam(name = "loginUsername", value = "admin"), // 用户名
    		@WebInitParam(name = "loginPassword", value = "admin"), // 密码
    		@WebInitParam(name = "resetEnable", value = "false")// 禁用HTML页面上的“Reset All”功能
    })
    public class DruidStatViewServlet extends StatViewServlet {
    
    }

最后，在启动类上面加上@ServletComponentScan

@SpringBootApplication
    //注意要加上@ServletComponentScan注解，否则Servlet无法生效
    @ServletComponentScan
    public class TomApplication {
    
    	public static void main(String[] args) {
    		SpringApplication.run(TomApplication.class, args);
    	}
    }

五，启动项目，登录[http://localhost:8080/druid/index.html][http_localhost_8080_druid_index.html] 查看监控情况

简直优秀。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMDA4NTM1_size_27_color_FFFFFF_t_70][]

### 二：将Redis作为mysql的二级缓存 ###

配置Redis

spring:
     redis:
        host: localhost
        port: 6379
        database: 1
        jedis:
          pool:
            max-idle: 8
            min-idle: 1
            max-active: 8
            max-wait: -1

接下来的步骤：①开启mybatis的二级缓存 ②重写缓存类  ③将mybatis的缓存替换为们重写的

## 重点：我们重写mybatis的cache类，它只会对配置文件类型的映射文件起作用 ##

主要的作用如下：

1.所有在映射文件里的 select 语句都将被缓存。  
2.所有在映射文件里 insert,update 和 delete 语句会清空缓存。  
3.缓存使用“最近很少使用”算法来回收  
4.缓存不会被设定的时间所清空。

一：开启二级缓存，配置中加一条就好

mybatis：
          configuration:
            cache-enabled: true

二：重写缓存类

这里也有一个问题，由于cache不是容器中的类，我们需要获得applicationContext

@Component
    public class ApplicationContextHolder implements ApplicationContextAware{
    
        private static ApplicationContext applicationContext;
    
        /**
         * 实现ApplicationContextAware接口的context注入函数, 将其存入静态变量.
         */
        public void setApplicationContext(ApplicationContext applicationContext) {
            ApplicationContextHolder.applicationContext = applicationContext; // NOSONAR
        }
    
        /**
         * 取得存储在静态变量中的ApplicationContext.
         */
        public static ApplicationContext getApplicationContext() {
            checkApplicationContext();
            return applicationContext;
        }
    
        /**
         * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
         */
        @SuppressWarnings("unchecked")
        public static <T> T getBean(String name) {
            checkApplicationContext();
            return (T) applicationContext.getBean(name);
        }
    
        /**
         * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
         */
        @SuppressWarnings("unchecked")
        public static <T> T getBean(Class<T> clazz) {
            checkApplicationContext();
            return (T) applicationContext.getBeansOfType(clazz);
        }
    
        /**
         * 清除applicationContext静态变量.
         */
        public static void cleanApplicationContext() {
            applicationContext = null;
        }
    
        private static void checkApplicationContext() {
            if (applicationContext == null) {
                throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");
            }
        }
    
    
    }

重写缓存类

public class RedisCache implements Cache {
        private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        private final String id; // cache instance id
        private RedisTemplate redisTemplate;
        private static final long EXPIRE_TIME_IN_MINUTES = 30; // redis过期时间
        public RedisCache(String id) {
            if (id == null) {
                throw new IllegalArgumentException("Cache instances require an ID");
            }
            this.id = id;
        }
        @Override
        public String getId() {
            return id;
        }
        /**
         * Put query result to redis
         *
         * @param key
         * @param value
         */
        @Override
        @SuppressWarnings("unchecked")
        public void putObject(Object key, Object value) {
            RedisTemplate redisTemplate = getRedisTemplate();
            ValueOperations opsForValue = redisTemplate.opsForValue();
            opsForValue.set(key, value, EXPIRE_TIME_IN_MINUTES, TimeUnit.MINUTES);
            System.out.println("放入结果到缓存");
        }
        /**
         * Get cached query result from redis
         *
         * @param key
         * @return
         */
        @Override
        public Object getObject(Object key) {
            RedisTemplate redisTemplate = getRedisTemplate();
            ValueOperations opsForValue = redisTemplate.opsForValue();
            System.out.println("获取结果从缓存");
            return opsForValue.get(key);
        }
        /**
         * Remove cached query result from redis
         *
         * @param key
         * @return
         */
        @Override
        @SuppressWarnings("unchecked")
        public Object removeObject(Object key) {
            RedisTemplate redisTemplate = getRedisTemplate();
            redisTemplate.delete(key);
            System.out.println("从缓存删除了");
            return null;
        }
        /**
         * Clears this cache instance
         */
        @Override
        public void clear() {
            RedisTemplate redisTemplate = getRedisTemplate();
            redisTemplate.execute((RedisCallback) connection -> {
                connection.flushDb();
                return null;
            });
            System.out.println("清空缓存");
        }
        @Override
        public int getSize() {
            return 0;
        }
        @Override
        public ReadWriteLock getReadWriteLock() {
            return readWriteLock;
        }
        private RedisTemplate getRedisTemplate() {
            if (redisTemplate == null) {
                redisTemplate = ApplicationContextHolder.getBean("redisTemplate");
            }
            return redisTemplate;
        }
    }

我在映射文件中写了增，删，查3个方法

<?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" >
    <mapper namespace="com.tom.mapper.teachMapper">
    	<cache type="com.tom.redisConfig.RedisCache"/>
    	<select id="getAll" resultType="teacher">
    	select * from teacher 
    	</select>
    	<select id="getById" resultType="teacher">
    	select * from teacher where id=#{id}
    	</select>
    	<insert id="save">
    	insert into teacher values(null,#{age},#{name})
    	</insert>
    	<delete id="delete">
    	delete from teacher where id=#{id}
    	</delete>
    </mapper>

OK！！让我看一下效果

结果为：select会添加数据到redis，insert，update，delete会清空缓存

但是这样子好像有点坑了，除select外的操作都要清空缓存，有待研究

[http_localhost_8080_druid_index.html]: http://localhost:8080/druid/index.html
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMDA4NTM1_size_27_color_FFFFFF_t_70]: /images/20220503/4aaf914c88e6485e8a73fdc4393eae56.png