Rest风格的后端web(SpringMVC)

前后端分离

天啦噜，我们希望『前后端分离』，前端的组件是css/js/html/图片，负责显示数据。数据打哪儿来？答案是后端。

后端服务器专门服务于前端，兢兢业业，勤勤恳恳，前端要什么，后端就给什么。

比如，前端向后端发出请求：www.ilovcecl.com/users/，目的是获取用户列表；逻辑复杂的后端服务器掐指一算，洞悉前端要的数据，便以JSON格式返回用户列表：

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[
  {
    "id": 3,
    "name": "Jerome",
    "age": 45,
    "salary": 30000
  },
  {
    "id": 4,
    "name": "Silvia",
    "age": 50,
    "salary": 40000
  }
]

可见，前后端分离的过程中，后端会以JSON格式返回数据，数据URI符合Rest风格（当然前后端通信除了Rest外还有其它架构）。

本文给出的正是以JSON风格返回数据、符合Rest风格的后端web项目，不依赖于xml配置，结构简单。

操作说明

你可以从GitHub下载项目源码：https://github.com/qiuyongchen/rcs-web/archive/v1.0.0.zip
使用IntelliJ IDEA导入项目，自动刷新pom依赖（部分IDEA版本有Bug无法刷新，请在shell中输入mvn clean package，手动刷新）；导入完成后配置tomcat，启动项目，访问http:localhost:8080/user/，耐心等待几秒钟，JSON即展现你眼前。

你也可以一步步地创建项目，添加文件，最后启动。

项目结构

本项目里，除了一个pom文件外，其余的均是java文件，不依赖传统的spring配置xml。
结构图：

src

pom文件

整个项目里唯一的配置有木有！！

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<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">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ilovecl</groupId>
    <artifactId>rcs-web</artifactId>
    <packaging>war</packaging>
    <version>1.0.0</version>
    <name>rcs-web</name>

    <properties>
        <springframework.version>4.2.0.RELEASE</springframework.version>
        <jackson.version>2.5.3</jackson.version>
    </properties>

    <dependencies>
        <!--SpringMVC Rest begin-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>${springframework.version}</version>
        </dependency>
        <!--SpringMVC Rest end-->

        <!--jackson begin-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <!--jackson end-->

        <!--servlet begin-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>
        <!--servlet end-->
    </dependencies>


    <!--编译管理-->
    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.2</version>
                    <configuration>
                        <source>1.7</source>
                        <target>1.7</target>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-war-plugin</artifactId>
                    <version>2.4</version>
                    <configuration>
                        <warSourceDirectory>src/main/java</warSourceDirectory>
                        <warName>rcs-web</warName>
                        <failOnMissingWebXml>false</failOnMissingWebXml>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>
        <finalName>rcs-web</finalName>
    </build>
</project>

项目初始化 WebInitilizer.java

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package config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

/**
 * spring会自动在源码包中(pom->warSourceDirectory)寻找继承
 * AbstractAnnotationConfigDispatcherServletInitializer的类，
 * 将其作为web项目的初始化类
 * Created by qiuyongchen on 2016/11/5.
 */
public class WebInitilizer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[]{WebConfiguration.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }

    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }

}

项目配置类 WebConfiguration.java

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package config;

/**
 * 如果源码直接放在pom->warSourceDirectory下，
 * 则basePackages为'.'即可;
 * 如果源码放在更深层级，
 * 则需指定目录层级，如'com.xxx'
 * Created by qiuyongchen on 2016/11/5.
 */

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = ".")
public class WebConfiguration {

}

控制类 RcsController.java

一个web项目最重要的类…

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package controller;

/**
 * 凡是带有注解@RestController的类，
 * 都被当做controller处理
 * Created by qiuyongchen on 2016/11/5.
 */

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
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.RestController;
import org.springframework.web.util.UriComponentsBuilder;

import model.User;
import service.UserService;

@RestController
public class RcsController {

    @Autowired
    UserService userService;  //Service which will do all data retrieval/manipulation work


    //-------------------Retrieve All Users--------------------------------------------------------

    @RequestMapping(value = "/user/", method = RequestMethod.GET)
    public ResponseEntity<List<User>> listAllUsers() {
        List<User> users = userService.findAllUsers();
        if (users.isEmpty()) {
            return new ResponseEntity<List<User>>(HttpStatus.NO_CONTENT);//You many decide to return HttpStatus.NOT_FOUND
        }
        return new ResponseEntity<List<User>>(users, HttpStatus.OK);
    }


    //-------------------Retrieve Single User--------------------------------------------------------

    @RequestMapping(value = "/user/{id}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<User> getUser(@PathVariable("id") long id) {
        System.out.println("Fetching User with id " + id);
        User user = userService.findById(id);
        if (user == null) {
            System.out.println("User with id " + id + " not found");
            return new ResponseEntity<User>(HttpStatus.NOT_FOUND);
        }
        return new ResponseEntity<User>(user, HttpStatus.OK);
    }


    //-------------------Create a User--------------------------------------------------------

    @RequestMapping(value = "/user/", method = RequestMethod.POST)
    public ResponseEntity<Void> createUser(@RequestBody User user, UriComponentsBuilder ucBuilder) {
        System.out.println("Creating User " + user.getName());

        if (userService.isUserExist(user)) {
            System.out.println("A User with name " + user.getName() + " already exist");
            return new ResponseEntity<Void>(HttpStatus.CONFLICT);
        }

        userService.saveUser(user);

        HttpHeaders headers = new HttpHeaders();
        headers.setLocation(ucBuilder.path("/user/{id}").buildAndExpand(user.getId()).toUri());
        return new ResponseEntity<Void>(headers, HttpStatus.CREATED);
    }


    //------------------- Update a User --------------------------------------------------------

    @RequestMapping(value = "/user/{id}", method = RequestMethod.PUT)
    public ResponseEntity<User> updateUser(@PathVariable("id") long id, @RequestBody User user) {
        System.out.println("Updating User " + id);

        User currentUser = userService.findById(id);

        if (currentUser == null) {
            System.out.println("User with id " + id + " not found");
            return new ResponseEntity<User>(HttpStatus.NOT_FOUND);
        }

        currentUser.setName(user.getName());
        currentUser.setAge(user.getAge());
        currentUser.setSalary(user.getSalary());

        userService.updateUser(currentUser);
        return new ResponseEntity<User>(currentUser, HttpStatus.OK);
    }

    //------------------- Delete a User --------------------------------------------------------

    @RequestMapping(value = "/user/{id}", method = RequestMethod.DELETE)
    public ResponseEntity<User> deleteUser(@PathVariable("id") long id) {
        System.out.println("Fetching & Deleting User with id " + id);

        User user = userService.findById(id);
        if (user == null) {
            System.out.println("Unable to delete. User with id " + id + " not found");
            return new ResponseEntity<User>(HttpStatus.NOT_FOUND);
        }

        userService.deleteUserById(id);
        return new ResponseEntity<User>(HttpStatus.NO_CONTENT);
    }

    //------------------- Delete All Users --------------------------------------------------------

    @RequestMapping(value = "/user/", method = RequestMethod.DELETE)
    public ResponseEntity<User> deleteAllUsers() {
        System.out.println("Deleting All Users");

        userService.deleteAllUsers();
        return new ResponseEntity<User>(HttpStatus.NO_CONTENT);
    }

}

Model类 User.java

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package model;

/**
 * Created by qiuyongchen on 2016/11/5.
 */
public class User {

    private long id;

    private String name;

    private int age;

    private double salary;

    public User() {
        id = 0;
    }

    public User(long id, String name, int age, double salary) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.salary = salary;
    }

    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 int getAge() {
        return age;
    }

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

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + (int) (id ^ (id >>> 32));
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (id != other.id)
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age
                + ", salary=" + salary + "]";
    }

}

Service接口 UserService.java

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package service;

import model.User;

import java.util.List;

/**
 * Created by qiuyongchen on 2016/11/5.
 */
public interface UserService {

    User findById(long id);

    User findByName(String name);

    void saveUser(User user);

    void updateUser(User user);

    void deleteUserById(long id);

    List<User> findAllUsers();

    void deleteAllUsers();

    public boolean isUserExist(User user);

}

Service接口实现类 UserServiceImpl.java

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package service.impl;

/**
 * Created by qiuyongchen on 2016/11/5.
 */

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import model.User;
import service.UserService;

@Service("userService")
@Transactional
public class UserServiceImpl implements UserService {

    private static final AtomicLong counter = new AtomicLong();

    private static List<User> users;

    static {
        users = populateDummyUsers();
    }

    public List<User> findAllUsers() {
        return users;
    }

    public User findById(long id) {
        for (User user : users) {
            if (user.getId() == id) {
                return user;
            }
        }
        return null;
    }

    public User findByName(String name) {
        for (User user : users) {
            if (user.getName().equalsIgnoreCase(name)) {
                return user;
            }
        }
        return null;
    }

    public void saveUser(User user) {
        user.setId(counter.incrementAndGet());
        users.add(user);
    }

    public void updateUser(User user) {
        int index = users.indexOf(user);
        users.set(index, user);
    }

    public void deleteUserById(long id) {

        for (Iterator<User> iterator = users.iterator(); iterator.hasNext(); ) {
            User user = iterator.next();
            if (user.getId() == id) {
                iterator.remove();
            }
        }
    }

    public boolean isUserExist(User user) {
        return findByName(user.getName()) != null;
    }

    private static List<User> populateDummyUsers() {
        List<User> users = new ArrayList<User>();
        users.add(new User(counter.incrementAndGet(), "Sam", 30, 70000));
        users.add(new User(counter.incrementAndGet(), "Tom", 40, 50000));
        users.add(new User(counter.incrementAndGet(), "Jerome", 45, 30000));
        users.add(new User(counter.incrementAndGet(), "Silvia", 50, 40000));
        return users;
    }

    public void deleteAllUsers() {
        users.clear();
    }

}