引子

我門知道一個程式的瓶頸在於資料庫，我門也知道記憶體的速度是大大快於硬碟的速度的。當我門需要重複的獲取相同的資料的時候，我門一次又一次的請求資料庫或者遠端服務，導致大量的時間耗費在資料庫查詢或者遠端方法的呼叫上，導致程式效能的惡化，這更是資料快取要解決的問題。

spring 快取支援

spring定義了 org.springframework.cache.CacheManager和org.springframework.cache.Cache介面來統一不同的快取技術。其中，CacheManager是Spring提供的各種快取技術抽象介面，Cache介面包含了快取的各種操作（增加、刪除獲得快取，我門一般不會直接和此介面打交道）

spring 支援的CacheManager

針對不同的快取技術，需要實現不同的CacheManager ,spring 定義瞭如下表的CacheManager實現。

實現任意一種CacheManager 的時候，需要註冊實現CacheManager的bean，當然每種快取技術都有很多額外的配置，但配置CacheManager 是必不可少的。

宣告式快取註解

spring提供了4個註解來宣告快取規則（又是使用註解式的AOP的一個生動例子），如表。

開啟宣告式快取

開啟宣告式快取支援非常簡單，只需要在配置類上使用@EnabelCaching 註解即可。

springBoot 的支援

在spring中國年使用快取技術的關鍵是配置CacheManager 而springbok 為我門自動配置了多個CacheManager的實現。在spring boot 環境下，使用快取技術只需要在專案中匯入相關快取技術的依賴包，並配置類使用@EnabelCaching開啟快取支援即可。

小例子

小例子是使用 springboot+jpa ＋cache 實現的。

例項步驟目錄

• 1.建立maven專案
• 2.資料庫配置
• 3.jpa配置和cache配置
• 4.編寫bean 和dao層
• 5.編寫service層
• 6.編寫controller
• 7.啟動cache
• 8.測試校驗

1.建立maven專案

新建maven 專案pom.xml檔案如下內容如下：

<?xml version="1.0" encoding="UTF-8"?>
<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.us</groupId>
    <artifactId>springboot-Cache</artifactId>
    <version>1.0-SNAPSHOT</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.3.0.RELEASE</version>
    </parent>

    <properties>
        <start-class>com.us.Application</start-class>

        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
    </properties>

    <!-- Add typical dependencies for a web application -->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-cache</artifactId>
        </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-web</artifactId>
        </dependency>

        <dependency>
            <groupId>net.sf.ehcache</groupId>
            <artifactId>ehcache</artifactId>
        </dependency>

        <!--db-->

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>6.0.5</version>
        </dependency>
        <dependency>
            <groupId>com.mchange</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.5.2</version>
            <exclusions>
                <exclusion>
                    <groupId>commons-logging</groupId>
                    <artifactId>commons-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

    </dependencies>

</project>

2.資料庫配置

在src/main/esouces目錄下新建application.properties 檔案，內容為資料庫連線資訊，如下：
application.properties

ms.db.driverClassName=com.mysql.jdbc.Driver
ms.db.url=jdbc:mysql://localhost:3306/cache?prepStmtCacheSize=517&cachePrepStmts=true&autoReconnect=true&useUnicode=true&characterEncoding=utf-8&useSSL=false&allowMultiQueries=true
ms.db.username=root
ms.db.password=xxxxxx
ms.db.maxActive=500

新建DBConfig.java 配置檔案，配置資料來源

package com.us.example.config;

/**
 * Created by yangyibo on 17/1/13.
 */
import java.beans.PropertyVetoException;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;
import com.mchange.v2.c3p0.ComboPooledDataSource;

@Configuration
public class DBConfig {
    @Autowired
    private Environment env;

    @Bean(name="dataSource")
    public ComboPooledDataSource dataSource() throws PropertyVetoException {
        ComboPooledDataSource dataSource = new ComboPooledDataSource();
        dataSource.setDriverClass(env.getProperty("ms.db.driverClassName"));
        dataSource.setJdbcUrl(env.getProperty("ms.db.url"));
        dataSource.setUser(env.getProperty("ms.db.username"));
        dataSource.setPassword(env.getProperty("ms.db.password"));
        dataSource.setMaxPoolSize(20);
        dataSource.setMinPoolSize(5);
        dataSource.setInitialPoolSize(10);
        dataSource.setMaxIdleTime(300);
        dataSource.setAcquireIncrement(5);
        dataSource.setIdleConnectionTestPeriod(60);

        return dataSource;
    }
}

資料庫設計，資料庫只有一張Person表，設計如下：

3.jpa配置

spring－data－ jpa 配置檔案如下：

package com.us.example.config;

import java.util.HashMap;
import java.util.Map;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

/**
 * Created by yangyibo on 17/1/13.
 */

@Configuration
@EnableJpaRepositories("com.us.example.dao")
@EnableTransactionManagement
@ComponentScan
public class JpaConfig {
    @Autowired
    private DataSource dataSource;

    @Bean
    public EntityManagerFactory entityManagerFactory() {
        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();

        LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
        factory.setJpaVendorAdapter(vendorAdapter);
        factory.setPackagesToScan("com.us.example.bean");
        factory.setDataSource(dataSource);


        Map<String, Object> jpaProperties = new HashMap<>();
        jpaProperties.put("hibernate.ejb.naming_strategy","org.hibernate.cfg.ImprovedNamingStrategy");
        jpaProperties.put("hibernate.jdbc.batch_size",50);
        factory.setJpaPropertyMap(jpaProperties);
        factory.afterPropertiesSet();
        return factory.getObject();
    }

    @Bean
    public PlatformTransactionManager transactionManager() {

        JpaTransactionManager txManager = new JpaTransactionManager();
        txManager.setEntityManagerFactory(entityManagerFactory());
        return txManager;
    }
}

4.編寫bean 和dao層

實體類 Person.java

package com.us.example.bean;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * Created by yangyibo on 17/1/13.
 */
@Entity
@Table(name = "Person")
public class Person {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    private Integer age;

    private String address;

    public Person() {
        super();
    }
    public Person(Long id, String name, Integer age, String address) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.address = address;
    }
    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;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }


}

dao層，PersonRepository.java

package com.us.example.dao;

import com.us.example.bean.Person;
import org.springframework.data.jpa.repository.JpaRepository;

/**
 * Created by yangyibo on 17/1/13.
 */
public interface PersonRepository extends JpaRepository<Person, Long> {

}

5.編寫service層

service 介面

package com.us.example.service;

import com.us.example.bean.Person;

/**
 * Created by yangyibo on 17/1/13.
 */
public  interface DemoService {
    public Person save(Person person);

    public void remove(Long id);

    public Person findOne(Person person);

}

實現：(重點，此處加快取)

package com.us.example.service.Impl;

import com.us.example.bean.Person;
import com.us.example.dao.PersonRepository;
import com.us.example.service.DemoService;
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;

/**
 * Created by yangyibo on 17/1/13.
 */
@Service
public class DemoServiceImpl implements DemoService {

    @Autowired
    private PersonRepository personRepository;

    @Override
    //@CachePut快取新增的或更新的資料到快取,其中快取名字是 people 。資料的key是person的id
    @CachePut(value = "people", key = "#person.id")
    public Person save(Person person) {
        Person p = personRepository.save(person);
        System.out.println("為id、key為:"+p.getId()+"資料做了快取");
        return p;
    }

    @Override
    //@CacheEvict 從快取people中刪除key為id 的資料
    @CacheEvict(value = "people")
    public void remove(Long id) {
        System.out.println("刪除了id、key為"+id+"的資料快取");
        //這裡不做實際刪除操作
    }

    @Override
    //@Cacheable快取key為person 的id 資料到快取people 中,如果沒有指定key則方法引數作為key儲存到快取中。
    @Cacheable(value = "people", key = "#person.id")
    public Person findOne(Person person) {
        Person p = personRepository.findOne(person.getId());
        System.out.println("為id、key為:"+p.getId()+"資料做了快取");
        return p;
    }

}

6.編寫controller

為了測試方便請求方式都用了get

package com.us.example.controller;
import com.us.example.bean.Person;
import com.us.example.service.DemoService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

/**
 * Created by yangyibo on 17/1/13.
 */
@RestController
public class CacheController {

    @Autowired
   private DemoService demoService;

    //http://localhost:8080/put?name=abel&age=23&address=shanghai
    @RequestMapping("/put")
    public Person put(Person person){
        return demoService.save(person);

    }

    //http://localhost:8080/able?id=1
    @RequestMapping("/able")
    @ResponseBody
    public Person cacheable(Person person){


        return demoService.findOne(person);

    }

    //http://localhost:8080/evit?id=1
    @RequestMapping("/evit")
    public String  evit(Long id){
        demoService.remove(id);
        return "ok";

    }


}

7.啟動cache

啟動類中要記得開啟快取配置。

package com.us.example;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import static org.springframework.boot.SpringApplication.*;

/**
 * Created by yangyibo on 17/1/13.
 */

@ComponentScan(basePackages ="com.us.example")
@SpringBootApplication
@EnableCaching
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = run(Application.class, args);
    }

}

8.測試校驗

檢驗able：

控制檯輸出：
“為id、key為:1資料做了快取“ 此時已經為此次查詢做了快取，再次查詢該條資料將不會出現此條語句，也就是不查詢資料庫了。

檢驗put

此時控制檯輸出為該條記錄做了快取：

然後再次呼叫able 方法，查詢該條資料，將不再查詢資料庫，直接從快取中讀取資料。

測試evit

在瀏覽器輸入：http://localhost:8080/evit?id=1（將該條記錄從快取中清楚，清除後，在次訪問該條記錄，將會重新將該記錄放入快取。）

控制檯輸出：

切換快取

1.切換為EhCache作為快取

pom.xml 檔案中新增依賴

<dependency>
            <groupId>net.sf.ehcache</groupId>
            <artifactId>ehcache</artifactId>
        </dependency>

在resource 資料夾下新建ehcache的配置檔案ehcache.xml 內容如下，此檔案spring boot 會自動掃描

<?xml version="1.0" encoding="UTF-8"?>
<ehcache>
    <!--切換為ehcache 快取時使用-->
<cache name="people" maxElementsInMemory="1000" />
</ehcache>

2.切換為Guava作為快取

只需要在pom中新增依賴

     <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>18.0</version>
        </dependency>

3.切換為redis作為快取

請看下篇部落格

本文參考：《JavaEE開發的顛覆者：Spring Boot實戰 》