Spring启动和缓存抽象

缓存是大多数应用程序的主要组成部分，只要我们设法避免磁盘访问，缓存就会保持强劲。 Spring对各种配置的缓存提供了强大的支持。您可以根据需要简单地开始，然后进行更多可定制的操作。

这将是spring提供的最简单的缓存形式的示例。
Spring默认带有一个内存缓存，它很容易设置。

让我们从gradle文件开始。

group 'com.gkatzioura'
version '1.0-SNAPSHOT'buildscript {repositories {mavenCentral()}dependencies {classpath("org.springframework.boot:spring-boot-gradle-plugin:1.4.2.RELEASE")}
}apply plugin: 'java'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'repositories {mavenCentral()
}sourceCompatibility = 1.8
targetCompatibility = 1.8dependencies {compile("org.springframework.boot:spring-boot-starter-web")compile("org.springframework.boot:spring-boot-starter-cache")compile("org.springframework.boot:spring-boot-starter")testCompile("junit:junit")
}bootRun {systemProperty "spring.profiles.active", "simple-cache"
}

由于同一项目将用于不同的缓存提供程序，因此会有多个spring配置文件。本教程的Spring配置文件将是简单缓存，因为我们将使用基于ConcurrentMap的缓存，该缓存恰好是默认缓存。

我们将实现一个应用程序，该应用程序将从本地文件系统中获取用户信息。该信息应位于users.json文件中

[{"userName":"user1","firstName":"User1","lastName":"First"},{"userName":"user2","firstName":"User2","lastName":"Second"},{"userName":"user3","firstName":"User3","lastName":"Third"},{"userName":"user4","firstName":"User4","lastName":"Fourth"}
]

我们还将为要检索的数据指定一个简单的模型。

package com.gkatzioura.caching.model;/*** Created by gkatzioura on 1/5/17.*/
public class UserPayload {private String userName;private String firstName;private String lastName;public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getFirstName() {return firstName;}public void setFirstName(String firstName) {this.firstName = firstName;}public String getLastName() {return lastName;}public void setLastName(String lastName) {this.lastName = lastName;}
}

然后，我们将添加一个将读取信息的bean。

package com.gkatzioura.caching.config;import com.fasterxml.jackson.databind.ObjectMapper;
import com.gkatzioura.caching.model.UserPayload;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.core.io.Resource;import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;/*** Created by gkatzioura on 1/5/17.*/
@Configuration
@Profile("simple-cache")
public class SimpleDataConfig {@Autowiredprivate ObjectMapper objectMapper;@Value("classpath:/users.json")private Resource usersJsonResource;@Beanpublic List<UserPayload> payloadUsers() throws IOException {try(InputStream inputStream = usersJsonResource.getInputStream()) {UserPayload[] payloadUsers = objectMapper.readValue(inputStream,UserPayload[].class);return Collections.unmodifiableList(Arrays.asList(payloadUsers));}}
}

显然，为了访问信息，我们将使用实例化的Bean包含所有用户信息。

下一步将是创建一个存储库接口，以指定将使用的方法。

package com.gkatzioura.caching.repository;import com.gkatzioura.caching.model.UserPayload;import java.util.List;/*** Created by gkatzioura on 1/6/17.*/
public interface UserRepository {List<UserPayload> fetchAllUsers();UserPayload firstUser();UserPayload userByFirstNameAndLastName(String firstName,String lastName);}

现在，让我们深入研究将包含所需缓存注释的实现。

package com.gkatzioura.caching.repository;import com.gkatzioura.caching.model.UserPayload;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cache.annotation.CacheEvict;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.context.annotation.Profile;
import org.springframework.stereotype.Repository;import java.util.List;
import java.util.Optional;/*** Created by gkatzioura on 12/30/16.*/
@Repository
@Profile("simple-cache")
public class UserRepositoryLocal implements UserRepository {@Autowiredprivate List<UserPayload> payloadUsers;private static final Logger LOGGER = LoggerFactory.getLogger(UserRepositoryLocal.class);@Override@Cacheable("alluserscache")public List<UserPayload> fetchAllUsers() {LOGGER.info("Fetching all users");return payloadUsers;}@Override@Cacheable(cacheNames = "usercache",key = "#root.methodName")public UserPayload firstUser() {LOGGER.info("fetching firstUser");return payloadUsers.get(0);}@Override@Cacheable(cacheNames = "usercache",key = "{#firstName,#lastName}")public UserPayload userByFirstNameAndLastName(String firstName,String lastName) {LOGGER.info("fetching user by firstname and lastname");Optional<UserPayload> user = payloadUsers.stream().filter(p-> p.getFirstName().equals(firstName)&&p.getLastName().equals(lastName)).findFirst();if(user.isPresent()) {return user.get();} else {return null;}}}

包含@Cacheable的方法将触发缓存填充，这与包含@CacheEvict的方法将触发缓存逐出相反。通过使用@Cacheable而不是仅指定将存储我们的值的缓存映射，我们还可以基于方法名称或方法参数来指定键。

因此，我们实现了方法缓存。例如，方法firstUser使用方法名称作为键，而方法userByFirstNameAndLastName使用方法参数以创建键。

带有@CacheEvict批注的两种方法将清空指定的缓存。

LocalCacheEvict将是处理驱逐的组件。

package com.gkatzioura.caching.repository;import org.springframework.cache.annotation.CacheEvict;
import org.springframework.context.annotation.Profile;
import org.springframework.stereotype.Component;/*** Created by gkatzioura on 1/7/17.*/
@Component
@Profile("simple-cache")
public class LocalCacheEvict {@CacheEvict(cacheNames = "alluserscache",allEntries = true)public void evictAllUsersCache() {}@CacheEvict(cacheNames = "usercache",allEntries = true)public void evictUserCache() {}}

由于我们使用非常简单的缓存形式，因此不支持驱逐ttl。因此，我们将仅针对此特定情况添加一个调度程序，该调度程序将在一定时间后退出缓存。

package com.gkatzioura.caching.scheduler;import com.gkatzioura.caching.repository.LocalCacheEvict;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Profile;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;/*** Created by gkatzioura on 1/7/17.*/
@Component
@Profile("simple-cache")
public class EvictScheduler {@Autowiredprivate LocalCacheEvict localCacheEvict;private static final Logger LOGGER = LoggerFactory.getLogger(EvictScheduler.class);@Scheduled(fixedDelay=10000)public void clearCaches() {LOGGER.info("Invalidating caches");localCacheEvict.evictUserCache();localCacheEvict.evictAllUsersCache();}}

最后，我们将使用控制器来调用指定的方法

package com.gkatzioura.caching.controller;import com.gkatzioura.caching.model.UserPayload;
import com.gkatzioura.caching.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;import java.util.List;/*** Created by gkatzioura on 12/30/16.*/
@RestController
public class UsersController {@Autowiredprivate UserRepository userRepository;@RequestMapping(path = "/users/all",method = RequestMethod.GET)public List<UserPayload> fetchUsers() {return userRepository.fetchAllUsers();}@RequestMapping(path = "/users/first",method = RequestMethod.GET)public UserPayload fetchFirst() {return userRepository.firstUser();}@RequestMapping(path = "/users/",method = RequestMethod.GET)public UserPayload findByFirstNameLastName(String firstName,String lastName ) {return userRepository.userByFirstNameAndLastName(firstName,lastName);}}

最后但并非最不重要的一点是，我们的Application类应包含两个额外的注释。为了启用调度程序，需要@EnableScheduling；为了启用缓存，需要@EnableCaching

package com.gkatzioura.caching;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.scheduling.annotation.EnableScheduling;/*** Created by gkatzioura on 12/30/16.*/
@SpringBootApplication
@EnableScheduling
@EnableCaching
public class Application {public static void main(String[] args) {SpringApplication.run(Application.class,args);}}

您可以在github上找到源代码。