一 點睛

雖然EhCache已經能夠適用很多應用場景，但是由於EhCache是程序內的快取框架，在叢集模式下時，各應用伺服器之間的快取都是獨立的，因此在不同伺服器的程序間會存在快取不一致的情況。即使EhCache提供了叢集環境下的快取同步策略，但是同步依然需要一定的時間，短暫的快取不一致依然存在。

在一些要求高一致性（任何資料變化都能及時的被查詢到）的系統和應用中，就不能再使用EhCache來解決了，這個時候使用集中式快取是個不錯的選擇，因此本篇將介紹如何在Spring Boot的快取支援中使用Redis進行資料快取。

二 實戰

1 新增依賴

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.21</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-cache</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-redis</artifactId>
    </dependency>
</dependencies>
 

2 實體類

package com.didispace.domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import java.io.Serializable;

/**
* @author 程式猿DD
* @version 1.0.0
* @date 16/3/21 下午3:35.
* @blog http://blog.didispace.com
*/
@Entity
public class User implements Serializable {

    @Id
    @GeneratedValue
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private Integer age;

    public User(){}

    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

}
 

3 資料訪問

package com.didispace.domain;

import org.springframework.cache.annotation.CacheConfig;
import org.springframework.cache.annotation.CachePut;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.data.jpa.repository.JpaRepository;


@CacheConfig(cacheNames = "users")
public interface UserRepository extends JpaRepository<User, Long> {

    @Cacheable(key = "#p0")
    User findByName(String name);

    @CachePut(key = "#p0.name")
    User save(User user);

}
 

4 啟動類

package com.didispace;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;

@SpringBootApplication
@EnableCaching
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

5 application.properties配置

spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
spring.jpa.properties.hibernate.hbm2ddl.auto=create-drop
spring.jpa.properties.hibernate.show_sql=true

spring.redis.host=localhost
spring.redis.port=6379
spring.redis.pool.max-idle=8
spring.redis.pool.min-idle=0
spring.redis.pool.max-active=8
spring.redis.pool.max-wait=-1

6 測試類

package com.didispace;

import com.didispace.domain.User;
import com.didispace.domain.UserRepository;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.cache.CacheManager;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(Application.class)
public class ApplicationTests {

    @Autowired
    private UserRepository userRepository;

    @Autowired
    private CacheManager cacheManager;

    @Before
    public void before() {
        userRepository.save(new User("AAA", 10));
    }

    @Test
    public void test() throws Exception {

        User u1 = userRepository.findByName("AAA");
        System.out.println("第一次查詢：" + u1.getAge());

        User u2 = userRepository.findByName("AAA");
        System.out.println("第二次查詢：" + u2.getAge());

        u1.setAge(20);
        userRepository.save(u1);
        User u3 = userRepository.findByName("AAA");
        System.out.println("第三次查詢：" + u3.getAge());

    }

}

三 測試結果

Hibernate: insert into user (age, name) values (?, ?)
第一次查詢：10
第二次查詢：10
Hibernate: select user0_.id as id1_0_0_, user0_.age as age2_0_0_, user0_.name as name3_0_0_ from user user0_ where user0_.id=?
Hibernate: update user set age=?, name=? where id=?
第三次查詢：20

可以看到，我們的第三次查詢獲得了正確的結果！同時，我們的第一次查詢也不是通過select查詢獲得的，因為在初始化資料的時候，呼叫save方法時，就已經將這條資料加入了redis快取中，因此後續的查詢就直接從redis中獲取了。