微服務(wù)架構(gòu)

微服務(wù)架構(gòu)近年來受到很多人的推崇，什么是微服務(wù)架構(gòu)？先參考一段定義：

微服務(wù)架構(gòu)（Microservices Architecture）是一種架構(gòu)風(fēng)格（Architectural Style）和設(shè)計(jì)模式，提倡將應(yīng)用分割成一系列細(xì)小的服務(wù)糠排，每個(gè)服務(wù)專注于單一業(yè)務(wù)功能，運(yùn)行于獨(dú)立的進(jìn)程中，服務(wù)之間邊界清晰螺垢，采用輕量級(jí)通信機(jī)制（如HTTP/REST）相互溝通、配合來實(shí)現(xiàn)完整的應(yīng)用赖歌，滿足業(yè)務(wù)和用戶的需求枉圃。
引用 - 基于容器云的微服務(wù)架構(gòu)實(shí)踐

簡(jiǎn)而言之就是服務(wù)輕量級(jí)化和模塊化，可獨(dú)立部署庐冯。其帶來的好處包括：解耦合程度更高孽亲，屏蔽底層復(fù)雜度展父；技術(shù)選型靈活赁酝，可方便其他模塊調(diào)用；易于部署和擴(kuò)展等旭等。與NodeJs等其他語言相比酌呆，Java相對(duì)來說實(shí)現(xiàn)微服務(wù)較為復(fù)雜一些，開發(fā)一個(gè)Web應(yīng)用需要經(jīng)歷編碼－編譯打包－部署到Web容器－啟動(dòng)運(yùn)行四步搔耕，但是開源框架Spring Boot的出現(xiàn)隙袁，讓Java微服務(wù)的實(shí)現(xiàn)變得很簡(jiǎn)單，由于內(nèi)嵌了Web服務(wù)器弃榨，無需“部署到Web容器”菩收，三步即可實(shí)現(xiàn)一個(gè)Web微服務(wù)。而且由于Spring Boot可以和Spring社區(qū)的其他框架進(jìn)行集成鲸睛，對(duì)于熟悉Spring的開發(fā)者來說很容易上手娜饵。下面本文會(huì)描述一個(gè)簡(jiǎn)易用戶管理微服務(wù)的實(shí)例，初步體驗(yàn)Spring Boot微服務(wù)開發(fā)官辈。

開發(fā)環(huán)境

• JDK 1.8
• Maven 3.0+
• Eclipse或其他IDE
• 本文程序可到github下載

添加依賴

maven的pom.xml配置文件

<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/maven-v4_0_0.xsd">
    <!-- inherit defaults from Spring Boot -->
    <parent>
    <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.0.RELEASE</version>
    </parent>

    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <!-- Spring Boot starter POMs -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- Spring Boot JPA POMs -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <!-- Spring Boot Test POMs -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
        </dependency>
        <!-- H2 POMs -->
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>
    </dependencies>

    <build>
        <finalName>webapp-springboot-angularjs-seed</finalName>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>  
</project>

這里首先繼承了spring-boot-starter-parent的默認(rèn)配置箱舞，然后依次引入

• spring-boot-starter-web 用來構(gòu)建REST微服務(wù)
• spring-boot-starter-data-jpa 利用JPA用來訪問數(shù)據(jù)庫
• h2 Spring Boot集成的內(nèi)存數(shù)據(jù)庫
• spring-boot-starter-test 用來構(gòu)建單元測(cè)試，內(nèi)含JUnit

程序結(jié)構(gòu)

|____sample
| |____webapp
| | |____ws
| | | |____App.java 啟動(dòng)程序
| | | |____controller
| | | | |____UserController.java 用戶管理的RESTful API
| | | |____domain
| | | | |____User.java 用戶信息
| | | |____exception
| | | | |____GlobalExceptionHandler.java 異常處理
| | | | |____UserNotFoundException.java 用戶不存在的異常
| | | |____repository
| | | | |____UserRepository.java 訪問用戶數(shù)據(jù)庫的接口
| | | |____rest
| | | | |____RestResultResponse.java Rest請(qǐng)求的狀態(tài)結(jié)果
| | | |____service
| | | | |____UserService.java 用戶管理的服務(wù)

用SpringApplication實(shí)現(xiàn)啟動(dòng)程序

import java.util.Arrays;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import com.leonlu.code.sample.webapp.ws.domain.User;
import com.leonlu.code.sample.webapp.ws.service.UserService;

@SpringBootApplication
public class App {
    @Bean
    CommandLineRunner init(UserService userService) {
        // add 5 new users after app are started
        return (evt) -> Arrays.asList("john,alex,mike,mary,jenny".split(","))
                            .forEach(item -> {
                                User user = new User(item, (int)(20 + Math.random() * 10));
                                userService.addUser(user);});
    }

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

• @SpringBootApplication相當(dāng)于@Configuration,@EnableAutoConfiguration,@ComponentScan三個(gè)注解拳亿。用于自動(dòng)完成Spring的配置和Bean的構(gòu)建晴股。
• main方法中的SpringApplication.run將啟動(dòng)內(nèi)嵌的Tomcat服務(wù)器，默認(rèn)端口為8080
• CommandLineRunner用于在啟動(dòng)后調(diào)用UserService肺魁，創(chuàng)建5個(gè)新用戶

利用RestController構(gòu)建Restful API

import java.util.Collection;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;
import com.leonlu.code.sample.webapp.ws.domain.User;
import com.leonlu.code.sample.webapp.ws.rest.RestResultResponse;
import com.leonlu.code.sample.webapp.ws.service.UserService;

@RestController
@RequestMapping("/user")
public class UserController {
    private UserService userService;
    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @RequestMapping(method = RequestMethod.GET)
    public Collection<User> getUsers() {
        return userService.getAllUsers();
    }

    @RequestMapping(method = RequestMethod.POST, consumes = "application/json")
    @ResponseStatus(HttpStatus.CREATED)
    public User addUser(@RequestBody User user) {
        if(user.getName() == null || user.getName().isEmpty()) {
            throw new IllegalArgumentException("Parameter 'name' must not be null or empty");
        }
        if(user.getAge() == null) {
            throw new IllegalArgumentException("Parameter 'age' must not be null or empty");
        }
        return userService.addUser(user);
    }

    @RequestMapping(value="/{id}", method = RequestMethod.GET)
    public User getUser(@PathVariable("id") Long id) {
        return userService.getUserById(id);
    }

    @RequestMapping(value="/{id}", method = RequestMethod.PUT, consumes = "application/json")
    public User updateUser(@PathVariable("id") String id, @RequestBody User user) {
        if(user.getName() == null && user.getAge() == null) {
            throw new IllegalArgumentException("Parameter 'name' and 'age' must not both be null");
        }
        return userService.addUser(user);
    }

    @RequestMapping(value="/{id}", method = RequestMethod.DELETE)
    public RestResultResponse deleteUser(@PathVariable("id") Long id) {
        try {
            userService.deleteUser(id);
            return new RestResultResponse(true);
        } catch(Exception e) {
            return new RestResultResponse(false, e.getMessage());
        }
    }
}

• UserController的構(gòu)造方法注入了userService电湘，后者提供了用戶管理的基本方法
• 所有方法的默認(rèn)的Http返回狀態(tài)是200，addUser方法通過添加@ResponseStatus(HttpStatus.CREATED)注解鹅经，將返回狀態(tài)設(shè)置為201寂呛。方法中拋出的異常的默認(rèn)Http返回狀態(tài)為500，而IllegalArgumentException的狀態(tài)由于在GlobalExceptionHandler中做了定義瘾晃，設(shè)置為了400 bad request.
• 除deleteUser()外贷痪，其余方法的返回結(jié)果皆為User對(duì)象，在Http結(jié)果中Spring Boot會(huì)自動(dòng)轉(zhuǎn)換為Json格式酗捌。而deleteUser()的返回結(jié)果RestResultResponse呢诬，是自定義的操作結(jié)果的狀態(tài)

利用CrudRepository訪問數(shù)據(jù)庫

import java.util.Optional;
import org.springframework.data.repository.CrudRepository;
import com.leonlu.code.sample.webapp.ws.domain.User;

public interface UserRepository extends CrudRepository<User, Long> {
    Optional<User> findByName(String name);
}

• CrudRepository提供了save(),findAll(), findOne()等通用的JPA方法，這里自定義了findByName方法胖缤，相當(dāng)于執(zhí)行"select a from User a where a.username = :username"查詢
• 這里僅需要定義UserRepository的接口尚镰，Spring Boot會(huì)自動(dòng)定義其實(shí)現(xiàn)類

UserService封裝用戶管理基本功能

import java.util.ArrayList;
import java.util.Collection;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.leonlu.code.sample.webapp.ws.domain.User;
import com.leonlu.code.sample.webapp.ws.exception.UserNotFoundException;
import com.leonlu.code.sample.webapp.ws.repository.UserRepository;

@Service
public class UserService {
    private UserRepository userRepository;

    @Autowired
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public Collection<User> getAllUsers() {
        Iterable<User> userIter = userRepository.findAll();
        ArrayList<User> userList = new ArrayList<User>();
        userIter.forEach(item -> {
            userList.add(item);
        });
        return userList;
    }

    public User getUserById(Long id) {
        User user =  userRepository.findOne(id);
        if(user == null) {
            throw new UserNotFoundException(id);
        }
        return user;
    }

    public User getUserByName(String name) {
        return userRepository.findByName(name)
            .orElseThrow(() -> new UserNotFoundException(name));
    }

    public User addUser(User user) {
        return userRepository.save(user);
    }

    public User updateUser(User user) {
        return userRepository.save(user);
    }

    public void deleteUser(Long id) {
        userRepository.delete(id);
    }
}

• 在getUserById()和getUserByName()中狗唉，對(duì)于不存在的用戶分俯，會(huì)拋出UserNotFoundException異常缸剪。這是一個(gè)自定義異常，其返回狀態(tài)為HttpStatus.NOT_FOUND唬渗，即404:

  import org.springframework.http.HttpStatus;
  import org.springframework.web.bind.annotation.ResponseStatus;
  
  @ResponseStatus(HttpStatus.NOT_FOUND)
  public class UserNotFoundException extends RuntimeException{
      public UserNotFoundException(Long userId) {
          super("could not find user '" + userId + "'.");
      }
      public UserNotFoundException(String userName) {
          super("could not find user '" + userName + "'.");
      }
  }
  

  示例效果如下：

  $ curl localhost:8080/user/12 -i
  HTTP/1.1 404
  Content-Type: application/json;charset=UTF-8
  Transfer-Encoding: chunked
  Date: Sun, 20 Aug 2016 14:00:41 GMT
  
  {"timestamp":1471788041171,"status":404,"error":"Not Found","exception":"com.leonlu.code.sample.webapp.ws.exception.UserNotFoundException","message":"could not find user '12'.","path":"/user/12"}
  

利用ControllerAdvice完成異常處理

import java.io.IOException;
import javax.servlet.http.HttpServletResponse;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(value = IllegalArgumentException.class)  
    public void handleException(Exception e, HttpServletResponse response) throws IOException{
        response.sendError(HttpStatus.BAD_REQUEST.value());
    }  
}

• 要修改Spring Boot的默認(rèn)異常返回結(jié)果，除了通過對(duì)自定義對(duì)異常添加@ResponseStatus注解之外（如上文中的UserNotFoundException）嫉鲸，開發(fā)者可通過@ExceptionHandler注解對(duì)某些異常的返回狀態(tài)和返回結(jié)果進(jìn)行自定義玄渗。
• @ControllerAdvice的作用是對(duì)全局的Controller進(jìn)行統(tǒng)一的設(shè)置

用Maven打包并運(yùn)行

• 打包 mvn clean package
• 運(yùn)行 java -jar JAR_NAME
• 用curl訪問localhost:8080/user驗(yàn)證結(jié)果

  $ curl -i localhost:8080/user
  HTTP/1.1 200
  Content-Type: application/json;charset=UTF-8
  Transfer-Encoding: chunked
  Date: Sun, 20 Aug 2016 14:32:06 GMT
  
  [{"id":1,"name":"john","age":29},{"id":2,"name":"alex","age":29},{"id":3,"name":"mike","age":27},{"id":4,"name":"mary","age":21},{"id":5,"name":"jenny","age":27}]
  

總結(jié)

基于Spring Boot可快速構(gòu)建Java微服務(wù)辈灼，而且官方提供了與Docker也榄，Redis甜紫，JMS等多種組件集成的功能囚霸，有豐富的文檔可供參考激才，值得大家嘗試瘸恼。

參考

1. Building REST services with Spring
2. Accessing Data with JPA
3. Spring Boot Reference Guide
4. SpringBoot : How to do Exception Handling in Rest Application
5. Post JSON to spring REST webservice

擴(kuò)展閱讀

1. 互聯(lián)網(wǎng)架構(gòu)為什么要做服務(wù)化压固？
2. 微服務(wù)架構(gòu)多“微”才合適靠闭？

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