簡單介紹REST

REST 表示狀態(tài)傳輸。這是一個體系結(jié)構(gòu)樣式，可用于設(shè)計網(wǎng)絡(luò)服務(wù)，可以被各種客戶端消耗。核心思想是，不使用如CORBA，RPC或SOAP復(fù)雜的機制在機器之間進行連接，簡單的 HTTP 用于使它們之間調(diào)用。

• 創(chuàng)建資源：應(yīng)該使用 HTTP POST
• 要獲取資源：應(yīng)該使用HTTP GET
• 更新資源：應(yīng)使用HTTP PUT
• 要刪除資源：應(yīng)使用HTTP DELETE

通常Rest 是基于Web服務(wù)返回JSON或XML數(shù)據(jù)格式作為響應(yīng)，雖然它并不僅僅限于這些類型。客戶端可以指定(使用 HTTP Accept 報頭)，他們所感興趣的資源類型，并且服務(wù)器可以返回資源，指定它所服務(wù)的內(nèi)容類型資源。 

基于REST的控制器

下面是一個可能基于 REST 的控制器，實現(xiàn)REST API。這里所說的“可能”，這意味著可以以另一種方式實現(xiàn)它，還是(或者更純粹的方式)符合REST風(fēng)格。

• GET 請求 /api/user/ 返回用戶的列表
• GET 請求  /api/user/1 返回ID為1的用戶
• POST 請求 /api/user/ 以用戶對象的JSON格式創(chuàng)建新的用戶
• PUT 請求 /api/user/3 以用戶對象作為JSON更新ID為3的用戶
• DELETE 請求 /api/user/4 刪除ID為4的用戶
• DELETE 請求 /api/user/ 刪除所有的用戶

package com.yiibai.springmvc.controller;

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 com.yiibai.springmvc.model.User;
import com.yiibai.springmvc.service.UserService;

@RestController
public class HelloWorldRestController {

	@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);
	}

}

@RestController : 首先，我們使用 Spring4 的新 @RestController 注釋。 它的注解消除了注釋每個以@ResponseBody的方法。@RestController本身注解為@ResponseBody，并且可以被視為@Controller和@ResponseBody的組合。

@RequestBody : 如果一個方法的參數(shù)都注解有@RequestBody，Spring將綁定傳入的 HTTP 請求體(在@RequestMapping提到該法的URL)到這個參數(shù)。這樣做 Spring 將[在后臺]使用HTTP消息轉(zhuǎn)換為HTTP請求主體轉(zhuǎn)換成域?qū)ο骩反序列化要求主體域?qū)ο骫的基礎(chǔ)上，接受或Content-Type頭請求。

@ResponseBody :如果一個方法被注解為@ResponseBody，Spring將綁定返回值傳出的 HTTP 響應(yīng)體。這樣做Spring將[在后臺]使用HTTP消息轉(zhuǎn)換器的返回值轉(zhuǎn)換為HTTP響應(yīng)體[序列化對象響應(yīng)正文]，根據(jù)內(nèi)容類型出現(xiàn)在請求的HTTP頭。 前面已經(jīng)提到，在 Spring4 可能會停止使用此注釋。

ResponseEntity是一個真正處理。 它代表了整個HTTP響應(yīng)。一件好事是你可以控制任何進入它東西?？梢灾付顟B(tài)碼，頭和主體。它自帶幾個構(gòu)造函數(shù)執(zhí)行你想要的 HTTP 響應(yīng)發(fā)送的信息。

@PathVariable 這種表示法表示方法參數(shù)應(yīng)綁定到一個 URI 模板變量[“{}”]。

基本上，@RestController，@RequestBody，ResponseEntity＆@PathVariable 都是用 Spring 4 實現(xiàn) REST API 需要知道的。此外，Spring提供了一些支持類來幫助你實現(xiàn)一些定制。

MediaType : 通過@RequestMapping注解，你還可以，指定要生產(chǎn)或消費的 MediaType(使用生產(chǎn)或消費屬性)，通過特定的控制器的方法，以進一步縮小映射。

部署并測試API，讓我們深入研究這個東西是如何工作的

它只是一個普通的控制器類，可部署的應(yīng)用程序的一部分。[完整下載的應(yīng)用程序代碼顯示在本教程文章最后，你可以直接部署到容器。先部署它，才能有這些可用服務(wù)，這里先詳細討論了每一個操作。部署的應(yīng)用程序并訪問：http://localhost:8080/Spring4MVCCRUDRestService.

為了測試這個API，這里使用一個外部客戶端POSTMAN(這是一個 Chrome 插件，下載安裝：http://www.getpostman.com/)。后面我們也將編寫我們自己的客戶端，也就幾分鐘的時間。

1. 檢索所有用戶

你可能想知道的響應(yīng)是如何發(fā)送 JSON 字符串，并在響應(yīng)中確認(rèn)Content-Type頭。這已在我們的項目Jackson庫中實現(xiàn)。

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.5.3</version>
</dependency>

關(guān)于Spring內(nèi)置轉(zhuǎn)換器，大部分的時間他們只需要某些庫在類路徑中以便進行轉(zhuǎn)換。當(dāng)然，有時我們也需要去適應(yīng)我們的 API/應(yīng)用程序也是如此。舉例來說，如果我們想為XML，我們應(yīng)標(biāo)注適當(dāng)JAXB標(biāo)注User類。

2. 檢索單用戶

3. 創(chuàng)建一個用戶

發(fā)送。您應(yīng)該看到HTTP200響應(yīng)，沒有主體(如API不發(fā)送主體任何東西)。但是，你應(yīng)該找一個Location頭指定位置新創(chuàng)建的用戶。

通過這種方式實現(xiàn)是常見的REST。但是，如果你想以 POST/ PUT請求的響應(yīng)主體發(fā)送內(nèi)容，也沒有人阻止你。

發(fā)送一個HTTP PUT請求以更新的用戶。一并發(fā)送新的用戶的信息。

請注意，我們收到的響應(yīng)體的這個時候。這是在控制器中的方法的實現(xiàn)發(fā)送。同樣，可以決定不發(fā)送更新信息的響應(yīng)體，并只發(fā)送位置標(biāo)頭(如創(chuàng)建)。

5. 刪除一個用戶

6. 刪除所有用戶

7. 用戶刪除后，驗證所有用戶

使用REST模板編寫REST客戶端

我們上面使用 Postman 是一個很好的客戶端測試 REST API 工具。但是，如果想從應(yīng)用程序消耗基于REST的Web服務(wù)，需要一個REST客戶端的應(yīng)用程序。其中最流行的 HTTP 客戶端就是 Apache HttpComponents HttpClient。 但在細節(jié)上使用這種訪問 REST 服務(wù)太低級。

Spring RestTemplate 可以來補救。 RestTemplate 提供對應(yīng)于六個主要的 HTTP 方法，使許多調(diào)用RESTful服務(wù)只需要一行代碼，就可執(zhí)行 REST最佳實踐的更高層次的方法。

• HTTP GET : getForObject, getForEntity
• HTTP PUT : put(String url, Object request, String…urlVariables)
• HTTP DELETE : delete
• HTTP POST : postForLocation(String url, Object request, String… urlVariables), postForObject(String url, Object request, Class responseType, String… uriVariables)
• HTTP HEAD : headForHeaders(String url, String… urlVariables)
• HTTP OPTIONS : optionsForAllow(String url, String… urlVariables)
• HTTP PATCH and others : exchange execute

package com.yiibai.springmvc;

import java.net.URI;
import java.util.LinkedHashMap;
import java.util.List;

import org.springframework.web.client.RestTemplate;

import com.yiibai.springmvc.model.User;

public class SpringRestTestClient {

	public static final String REST_SERVICE_URI = "http://localhost:8080/Spring4MVCCRUDRestService";
	
	/* GET */
	@SuppressWarnings("unchecked")
	private static void listAllUsers(){
		System.out.println("Testing listAllUsers API-----------");
		
		RestTemplate restTemplate = new RestTemplate();
		List<LinkedHashMap<String, Object>> usersMap = restTemplate.getForObject(REST_SERVICE_URI+"/user/", List.class);
		
		if(usersMap!=null){
			for(LinkedHashMap<String, Object> map : usersMap){
	            System.out.println("User : id="+map.get("id")+", Name="+map.get("name")+", Age="+map.get("age")+", Salary="+map.get("salary"));;
	        }
		}else{
			System.out.println("No user exist----------");
		}
	}
	
	/* GET */
	private static void getUser(){
		System.out.println("Testing getUser API----------");
		RestTemplate restTemplate = new RestTemplate();
        User user = restTemplate.getForObject(REST_SERVICE_URI+"/user/1", User.class);
        System.out.println(user);
	}
	
	/* POST */
    private static void createUser() {
		System.out.println("Testing create User API----------");
    	RestTemplate restTemplate = new RestTemplate();
        User user = new User(0,"Sarah",51,134);
        URI uri = restTemplate.postForLocation(REST_SERVICE_URI+"/user/", user, User.class);
        System.out.println("Location : "+uri.toASCIIString());
    }

    /* PUT */
    private static void updateUser() {
		System.out.println("Testing update User API----------");
        RestTemplate restTemplate = new RestTemplate();
        User user  = new User(1,"Tomy",33, 70000);
        restTemplate.put(REST_SERVICE_URI+"/user/1", user);
        System.out.println(user);
    }

    /* DELETE */
    private static void deleteUser() {
		System.out.println("Testing delete User API----------");
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.delete(REST_SERVICE_URI+"/user/3");
    }


    /* DELETE */
    private static void deleteAllUsers() {
		System.out.println("Testing all delete Users API----------");
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.delete(REST_SERVICE_URI+"/user/");
    }

    public static void main(String args[]){
		listAllUsers();
		getUser();
		createUser();
		listAllUsers();
		updateUser();
		listAllUsers();
		deleteUser();
		listAllUsers();
		deleteAllUsers();
		listAllUsers();
    }
}

Testing listAllUsers API-----------
User : id=1, Name=Sam, Age=30, Salary=70000.0
User : id=2, Name=Tom, Age=40, Salary=50000.0
User : id=3, Name=Jerome, Age=45, Salary=30000.0
User : id=4, Name=Silvia, Age=50, Salary=40000.0
Testing getUser API----------
User [id=1, name=Sam, age=30, salary=70000.0]
Testing create User API----------
Location : http://localhost:8080/Spring4MVCCRUDRestService/user/5
Testing listAllUsers API-----------
User : id=1, Name=Sam, Age=30, Salary=70000.0
User : id=2, Name=Tom, Age=40, Salary=50000.0
User : id=3, Name=Jerome, Age=45, Salary=30000.0
User : id=4, Name=Silvia, Age=50, Salary=40000.0
User : id=5, Name=Sarah, Age=51, Salary=134.0
Testing update User API----------
User [id=1, name=Tomy, age=33, salary=70000.0]
Testing listAllUsers API-----------
User : id=1, Name=Tomy, Age=33, Salary=70000.0
User : id=2, Name=Tom, Age=40, Salary=50000.0
User : id=3, Name=Jerome, Age=45, Salary=30000.0
User : id=4, Name=Silvia, Age=50, Salary=40000.0
User : id=5, Name=Sarah, Age=51, Salary=134.0
Testing delete User API----------
Testing listAllUsers API-----------
User : id=1, Name=Tomy, Age=33, Salary=70000.0
User : id=2, Name=Tom, Age=40, Salary=50000.0
User : id=4, Name=Silvia, Age=50, Salary=40000.0
User : id=5, Name=Sarah, Age=51, Salary=134.0
Testing all delete Users API----------
Testing listAllUsers API-----------
No user exist----------

完整的實例

工程結(jié)構(gòu)

聲明項目的依賴關(guān)系

<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.yiibai.springmvc</groupId>
  <artifactId>Spring4MVCCRUDRestService</artifactId>
  <packaging>war</packaging>
  <version>1.0.0</version>
  <name>Spring4MVCCRUDRestService Maven Webapp</name>

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

	<dependencies>
		<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>

		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
		    <artifactId>jackson-databind</artifactId>
		    <version>${jackson.version}</version>
		</dependency>
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>3.1.0</version>
		</dependency>
			
	</dependencies>


	<build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>org.apache.maven.plugins</groupId>
					<artifactId>maven-war-plugin</artifactId>
					<version>2.4</version>
					<configuration>
						<warSourceDirectory>src/main/webapp</warSourceDirectory>
						<warName>Spring4MVCCRUDRestService</warName>
						<failOnMissingWebXml>false</failOnMissingWebXml>
					</configuration>
				</plugin>
			</plugins>
		</pluginManagement>

		<finalName>Spring4MVCCRUDRestService</finalName>
	</build>
</project>

User Service

package com.yiibai.springmvc.service;

import java.util.List;
import com.yiibai.springmvc.model.User;

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);
	
}

package com.yiibai.springmvc.service;

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 com.yiibai.springmvc.model.User;

@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();
	}

}

Model class

package com.yiibai.springmvc.model;

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 + "]";
	}
}

Configuration class

package com.yiibai.springmvc.configuration;

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

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.yiibai.springmvc")
public class HelloWorldConfiguration {
	
}

Initialization Class

package com.yiibai.springmvc.configuration;

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

public class HelloWorldInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
 
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { HelloWorldConfiguration.class };
    }
  
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }
  
    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
 
}

添加CORS支持REST API

” No ‘Access-Control-Allow-Origin’ 的頭存在于所請求的資源。 Origin ‘http://127.0.0.1:8080′ is therefore not allowed access.” OR” XMLHttpRequest cannot load http://abc.com/bla. Origin http://localhost:12345 is not allowed by Access-Control-Allow-Origin.” are common in such case.

解決辦法是跨域資源共享。基本上，在服務(wù)器端，我們可以返回更多的CORS系統(tǒng)的訪問控制頭在響應(yīng)中，這將最終允許進一步域間的通信。

package com.yiibai.springmvc.configuration;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;


public class CORSFilter implements Filter {

	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
		System.out.println("Filtering on...........................................................");
		HttpServletResponse response = (HttpServletResponse) res;
		response.setHeader("Access-Control-Allow-Origin", "*");
		response.setHeader("Access-Control-Allow-Methods", "POST, GET, PUT, OPTIONS, DELETE");
		response.setHeader("Access-Control-Max-Age", "3600");
		response.setHeader("Access-Control-Allow-Headers", "x-requested-with");
		chain.doFilter(req, res);
	}

	public void init(FilterConfig filterConfig) {}

	public void destroy() {}

}

package com.yiibai.springmvc.configuration;

import javax.servlet.Filter;

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

public class HelloWorldInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
 
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { HelloWorldConfiguration.class };
    }
  
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }
  
    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
    
    @Override
    protected Filter[] getServletFilters() {
    	Filter [] singleton = { new CORSFilter()};
    	return singleton;
    }
 
}