使用JSON和Jersey的Java RESTful Web服务

使用Jersey创建一个RESTful Web服务来产生JSON响应。 RESTful Web服务可以配置为生成不同类型的响应，如XML，JSON，html，纯文本和大多数MIME类型。本篇文章完成设置mime类型以生成JSON响应。如果你刚刚开始使用RESTful Web服务，可以先了解下Jersey的RESTful Web服务的基本信息。

@Produces Annotation

我们可以使用@Produces注释为资源指定MIME类型表示。例如，我们可以将mime类型指定为text / html作为@Produces（“text / html”）。此@Produces注释可以在类级别和方法级别指定。方法默认为类级别注释，方法级别注释覆盖类级别注释的值。

@Produces({"application/xml", "application/json"})

当资源能够产生多个MIME类型时，则基于请求的Accept头选择类型。 accept头可以是以下格式的，例如，Accept: application/json接受标头可以指定多个MIME类型，在这种情况下，会考虑由接受标头指定的首选项。如果首选项相等，则选择@Produces注释中的第一个出现MIME类型作为响应。

Web服务中的JSON响应

要更改已写入以提供XML响应或创建新响应的Web服务，我们只需要添加两件事。

使用@Produces注释并添加MIME类型应用程序/ json。
添加相关JAR文件以生成JSON响应。
SEVERE: MessageBodyWriter not found for media type={application/json, q=1000}, type=class java.util.ArrayList, genericType=java.util.List<com.javapapers.webservices.rest.jersey.Animal>.
如果您没有添加依赖的Jar文件以生成JSON响应，您将收到上述错误。应该添加以下Maven依赖项来生成JSON

<dependency><groupId>org.glassfish.jersey.media</groupId><artifactId>jersey-media-moxy</artifactId><version>2.17</version>
</dependency>

带有JSON示例的RESTful Web服务

在前面的教程中，我们看到了使用Jersey创建一个CRUD RESTful Web服务。我们将根据该Web服务教程中提供的示例创建一个示例Web服务。有多个依赖jar需要运行这个例子，它更好地使用MAVEN来管理JAR依赖。通过我的Maven 10分钟教程，如果你是新的。

pom.xml和Maven依赖

<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>JSONRESTfulServices</groupId><artifactId>JSONRESTfulServices</artifactId><version>0.0.1-SNAPSHOT</version><packaging>war</packaging><dependencies><dependency><groupId>org.glassfish.jersey.core</groupId><artifactId>jersey-server</artifactId><version>2.17</version></dependency><dependency><groupId>org.glassfish.jersey.containers</groupId><artifactId>jersey-container-servlet-core</artifactId><version>2.17</version></dependency><dependency><groupId>org.glassfish.jersey.media</groupId><artifactId>jersey-media-moxy</artifactId><version>2.17</version></dependency></dependencies><build><sourceDirectory>src</sourceDirectory><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.1</version><configuration><source>1.7</source><target>1.7</target></configuration></plugin><plugin><artifactId>maven-war-plugin</artifactId><version>2.3</version><configuration><warSourceDirectory>WebContent</warSourceDirectory><failOnMissingWebXml>false</failOnMissingWebXml></configuration></plugin></plugins></build>
</project>

Java RESTful Web服务与JSON示例源代码
ProductsResource.java
此RESTful服务资源使用@Produces（{MediaType.APPLICATION_XML，MediaType.APPLICATION_JSON}），并且我们已经通过Maven添加了相关的JAR文件以生成JSON响应。现在，如果这个Web服务接收到一个带有请求头Accept：application / json的请求，它将发出一个JSON响应。

package com.javapapers.webservices.rest.jersey;import java.io.IOException;
import java.util.List;import javax.servlet.http.HttpServletResponse;
import javax.ws.rs.Consumes;
import javax.ws.rs.FormParam;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.UriInfo;@Path("/products")
public class ProductsResource {@ContextUriInfo uriInfo;@ContextRequest request;ProductService productService;public ProductsResource() {productService = new ProductService();}@GET@Produces({ MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON })public List<Product> getProducts() {return productService.getProductAsList();}@GET@Produces(MediaType.TEXT_XML)public List<Product> getProductsAsHtml() {return productService.getProductAsList();}// URI: /rest/products/count@GET@Path("count")@Produces(MediaType.TEXT_PLAIN)public String getCount() {return String.valueOf(productService.getProductsCount());}@POST@Produces(MediaType.TEXT_HTML)@Consumes(MediaType.APPLICATION_FORM_URLENCODED)public void createProduct(@FormParam("id") String id,@FormParam("productname") String name,@FormParam("productcategory") String category,@Context HttpServletResponse servletResponse) throws IOException {Product product = new Product(id, name, category);productService.createProduct(product);servletResponse.sendRedirect("./products/");}@Path("{product}")public ProductResource getProduct(@PathParam("product") String id) {return new ProductResource(uriInfo, request, id);}}

ProductService.java

package com.javapapers.webservices.rest.jersey;import javax.ws.rs.Consumes;
import javax.ws.rs.DELETE;
import javax.ws.rs.GET;
import javax.ws.rs.PUT;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;
import javax.xml.bind.JAXBElement;public class ProductResource {@ContextUriInfo uriInfo;@ContextRequest request;String id;ProductService productService;public ProductResource(UriInfo uriInfo, Request request, String id) {this.uriInfo = uriInfo;this.request = request;this.id = id;productService = new ProductService();}@GET@Produces({ MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON })public Product getProduct() {Product product = productService.getProduct(id);return product;}@GET@Produces(MediaType.TEXT_XML)public Product getProductAsHtml() {Product product = productService.getProduct(id);return product;}@PUT@Consumes(MediaType.APPLICATION_XML)public Response putProduct(JAXBElement<Product> productElement) {Product product = productElement.getValue();Response response;if (productService.getProducts().containsKey(product.getId())) {response = Response.noContent().build();} else {response = Response.created(uriInfo.getAbsolutePath()).build();}productService.createProduct(product);return response;}@DELETEpublic void deleteProduct() {productService.deleteProduct(id);}}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"><display-name>JSON RESTful Services</display-name><servlet><servlet-name>JSON RESTful Service</servlet-name><servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class><init-param><param-name>jersey.config.server.provider.packages</param-name><param-value>com.javapapers.webservices.rest.jersey</param-value></init-param><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>JSON RESTful Service</servlet-name><url-pattern>/rest/*</url-pattern></servlet-mapping>
</web-app>

其他文件

package com.javapapers.webservices.rest.jersey;import javax.xml.bind.annotation.XmlRootElement;@XmlRootElement
public class Product {private String id;private String name;private String category;public Product() {}public Product(String id, String name, String category) {super();this.id = id;this.name = name;this.category = category;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getCategory() {return category;}public void setCategory(String category) {this.category = category;}}

package com.javapapers.webservices.rest.jersey;import java.util.HashMap;
import java.util.Map;public enum ProductDao {instance;private Map<String, Product> products = new HashMap<String, Product>();private ProductDao() {// pumping-in some default dataProduct product = new Product("1001", "iPhone 5S", "Mobile");products.put("1", product);product = new Product("1002", "Sony MDR-XD200", "Headphone");products.put("2", product);product = new Product("1003", "Bose Wave II", "Home Audio");products.put("3", product);}public Map<String, Product> getProducts() {return products;}}

package com.javapapers.webservices.rest.jersey;import java.util.ArrayList;
import java.util.List;
import java.util.Map;public class ProductService {ProductDao productDao;public ProductService() {productDao = ProductDao.instance;}public void createProduct(Product product) {productDao.getProducts().put(product.getId(), product);}public Product getProduct(String id) {return productDao.getProducts().get(id);}public Map<String, Product> getProducts() {return productDao.getProducts();}public List<Product> getProductAsList() {List<Product> productList = new ArrayList<Product>();productList.addAll(productDao.getProducts().values());return productList;}public int getProductsCount() {return productDao.getProducts().size();}public void deleteProduct(String id) {productDao.getProducts().remove(id);}}

RESTful Web服务客户端
我们需要向Web服务添加一个“Header”请求。

JSON响应：

XML响应：