构建一个RESTful Web服务

构建一个RESTful Web服务

构建一个RESTful Web服务

Building a RESTful Web Service

此教程将告诉你如何使用Spring创建一个”hello world”RESTful web服务

This guide walks you through the process of creating a “hello world” RESTful web service with Spring.

将要做什么

What you’ll build

你将构建一个接受HTTP GET请求的服务:

You’ll build a service that will accept HTTP GET requests at:

http://localhost:8080/greeting

并返回表示问候的一个JSON响应。

and respond with a JSON representation of a greeting:

{"id":1,"content":"Hello, World!"}

也可以通过备选参数name来自定义问候:

You can customize the greeting with an optional name parameter in the query string:

http://localhost:8080/greeting?name=User

name参数将覆写并替代响应中默认的”World”:

The name parameter value overrides the default value of “World” and is reflected in the response:

{"id":1,"content":"Hello, User!"}

需要些什么

What you’ll need

如何完成此教程

How to complete this guide

与大多数Spring的入门教程相似,你可以从头开始并完成每一步,或者你也可以跳过你熟悉的设置步骤。无论怎样,你最终应当以有效代码结束。

Like most Spring Getting Started guides, you can start from scratch and complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

如果从头开始,可参考使用Gradle构建

To start from scratch, move on to Build with Gradle.

如果要跳过基本步骤,按如下步骤:

To skip the basics, do the following:

  • 下载并解压此教程的源码仓库,或者使用Git进行clone:git clone https://github.com/spring-guides/gs-rest-service.git
  • cd into gs-rest-service/initial
  • 跳至创建一个资源表示类.

当你完成时,你可以与gs-rest-service/complete中的代码对比检查。

When you’re finished, you can check your results against the code in gs-rest-service/complete.

创建一个资源表示类

Create a resource representation class

现在你已经配置好工程与构建系统,现在可以创建web服务了。

Now that you’ve set up the project and build system, you can create your web service.

首先要想清楚服务交互。

Begin the process by thinking about service interactions.

此服务将处理/greetingGET请求,请求字符串中有个name可选参数。GET请求将返回一个200 OK响应的,响应体是表示问候的一个字符串。看起来应该如下:

The service will handle GET requests for /greeting, optionally with a name parameter in the query string. The GET request should return a 200 OK response with JSON in the body that represents a greeting. It should look something like this:

{
    "id": 1,
    "content": "Hello, World!"
}

id字段表示问候的唯一id,content表示问候的文本。

The id field is a unique identifier for the greeting, and content is the textual representation of the greeting.

为了模型化此问候,你可以创建一个资源表示类。提供一个java对象类,包括字段、构造、idcontent数据的访问等:

To model the greeting representation, you create a resource representation class. Provide a plain old java object with fields, constructors, and accessors for the id and content data:

src/main/java/hello/Greeting.java

package hello;

public class Greeting {

    private final long id;
    private final String content;

    public Greeting(long id, String content) {
        this.id = id;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }
}

在下面的步骤中,Spring将使用Jackson JSON库把Greeting类型实例自动转换为JSON。

As you see in steps below, Spring uses the Jackson JSON library to automatically marshal instances of type Greeting into JSON.

接下来你将创建提供问候功能的资源控制器。

Next you create the resource controller that will serve these greetings.

创建一个资源控制器

Create a resource controller

使用Spring构建RESTful web服务,需要用一个控制器来处理HTTP请求。此组件可以使用@RestController注解来声明,下面的GreetingController处理/greetingGET请求,并返回一个Greeting类实例:

In Spring’s approach to building RESTful web services, HTTP requests are handled by a controller. These components are easily identified by the @RestController annotation, and the GreetingController below handles GET requests for /greeting by returning a new instance of the Greeting class:

src/main/java/hello/GreetingController.java

package hello;

import java.util.concurrent.atomic.AtomicLong;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    private static final String template = "Hello, %s!";
    private final AtomicLong counter = new AtomicLong();

    @RequestMapping("/greeting")
    public Greeting greeting(@RequestParam(value="name", defaultValue="World") String name) {
        return new Greeting(counter.incrementAndGet(),
                            String.format(template, name));
    }
}

此控制器虽然比较简洁且简单,但后台也有大量的细节。让我们来一步步分解。

This controller is concise and simple, but there’s plenty going on under the hood. Let’s break it down step by step.

@RequestMapping注解确保/greeting的HTTP请求映射到greeting()方法上。

The @RequestMapping annotation ensures that HTTP requests to /greeting are mapped to the greeting() method.

上面的例子并没有指定是GETPUT, POST等,因为@RequestMapping默认映射所有的HTTTP操作。使用@RequestMapping(method=GET)来限定其映射。

The above example does not specify GET vs. PUT, POST, and so forth, because @RequestMapping maps all HTTP operations by default. Use @RequestMapping(method=GET) to narrow this mapping.

@RequestParam将请求中的字符串参数name绑定到greeting()方法中的name参数上。如果请求中没有name参数,则将使用指定的默认值defaultValue的”World”。

@RequestParam binds the value of the query string parameter name into the name parameter of the greeting() method. If the name parameter is absent in the request, the defaultValue of “World” is used.

方法体的实现中创建并返回了一个新的Greeting对象,其中包含idcontent属性,值分别为counter对象的下一个值,和使用问候template来格式化指定的name

The implementation of the method body creates and returns a new Greeting object with id and content attributes based on the next value from the counter, and formats the given name by using the greeting template.

传统MVC控制器和RESTful web服务控制器的一个主要区别是HTTP响应体的创建方式。不同于依赖于视图技术使用服务端渲染将问候数据转为HTML,RESTful web服务控制器简单地填充并返回一个Greeting对象。对象数据将直接通过HTTP响应输出为JSON。

A key difference between a traditional MVC controller and the RESTful web service controller above is the way that the HTTP response body is created. Rather than relying on a view technology to perform server-side rendering of the greeting data to HTML, this RESTful web service controller simply populates and returns a Greeting object. The object data will be written directly to the HTTP response as JSON.

上面代码使用了Spring 4中新的注解@RestController,标记此类为控制类并且每个方法都返回对象而不是视图。相当于@Controller@ResponseBody的合并简化版。

This code uses Spring 4’s new @RestController annotation, which marks the class as a controller where every method returns a domain object instead of a view. It’s shorthand for @Controller and @ResponseBody rolled together.

Greeting对象必须转换为JSON。因为Spring的HTTP消息转换器的支持,你不需要手动转换。因为Jackson 2在classpath中,将自动选择Spring的MappingJackson2HttpMessageConverterGreeting实例转换为JSON。

The Greeting object must be converted to JSON. Thanks to Spring’s HTTP message converter support, you don’t need to do this conversion manually. Because Jackson 2 is on the classpath, Spring’s MappingJackson2HttpMessageConverter is automatically chosen to convert the Greeting instance to JSON.

让应用可执行

Make the application executable

虽然可以将服务打包作为传统的WAR包,并部署在一个外部应用服务上,但下面展示的更简单的方法是创建一个独立的应用。你可以将所有东西打包为一个独立的可执行的JAR包,由Java main()方法驱动。这样一来,就代替了使用外部实例进行部署,转而使用Spring支持的内嵌Tomcat servlet容器作为HTTP运行时。

Although it is possible to package this service as a traditional WAR file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main() method. Along the way, you use Spring’s support for embedding the Tomcat servlet container as the HTTP runtime, instead of deploying to an external instance.

src/main/java/hello/Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

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

@SpringBootApplication是一个方便的注解,可以添加如下:

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration标记此类作为应用上下文的bean定义来源。
  • @EnableAutoConfiguration告诉Spring Boot基于classpath设置、其他bean或者各种属性设置来开始添加bean。
  • 通常你会在Spring MVC应用中添加@EnableWebMvc,如果在classpath中发现spring-webmvc,则Spring Boot会自动添加。此注解会标记应用为web应用,并激活一些关键行为例如设置一个DispatcherServlet
  • @ComponentScan告诉Spring在hello包中寻找其他组件、配置、服务等,也允许找到controllers。
  • @Configuration tags the class as a source of bean definitions for the application context.
  • @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.
  • Normally you would add @EnableWebMvc for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as setting up a DispatcherServlet.
  • @ComponentScan tells Spring to look for other components, configurations, and services in the hello package, allowing it to find the controllers.

main()方法中使用了Spring Boot的SpringApplication.run()方法来加载一个应用。你注意到了没有任何XML吗?同样也没有web.xml文件。此web应用是100%纯Java并且你不要处理任何基础架构方面的配置。

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.

创建一个可执行的JAR

Build an executable JAR

你可以使用Gradle或者Maven命令行来运行此应用。或者你可以构建一个包含所有必须依赖、类、资源的独立可执行JAR文件,并运行它。这样可以更简单地在整个部署声明周期中,包括不同的环境等,将此服务作为应用来迁移、版本管理以及部署。

You can run the application from the command line with Gradle or Maven. Or you can build a single executable JAR file that contains all the necessary dependencies, classes, and resources, and run that. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

如果使用Gradle,可以使用./gradlew bootRun来运行应用。或者可以使用./gradlew build构建JAR文件。然后可以运行此JAR文件:

If you are using Gradle, you can run the application using ./gradlew bootRun. Or you can build the JAR file using ./gradlew build. Then you can run the JAR file:

java -jar build/libs/gs-rest-service-0.1.0.jar

如果使用Maven,可以使用./mvnw spring-boot:run来运行应用。或者可以使用./mvnw clean package构建JAR文件。然后可以运行此JAR文件:

If you are using Maven, you can run the application using ./mvnw spring-boot:run. Or you can build the JAR file with ./mvnw clean package. Then you can run the JAR file:

java -jar target/gs-rest-service-0.1.0.jar

上述过程将创建一个可运行的JAR。你也可以选择构建一个传统的WAR文件。

The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.

然后将显示日志输出。服务将在几秒内被建立并运行。

Logging output is displayed. The service should be up and running within a few seconds.

测试此服务

Test the service

现在服务已经就绪,通过http://localhost:8080/greeting访问,将看见如下输出:

Now that the service is up, visit http://localhost:8080/greeting, where you see:

{"id":1,"content":"Hello, World!"}

在请求字符串参数中提供一个name,如http://localhost:8080/greeting?name=User。注意content属性的值由”Hello, World!”变为了”Hello User!”:

Provide a name query string parameter with http://localhost:8080/greeting?name=User. Notice how the value of the content attribute changes from “Hello, World!” to “Hello User!”:

{"id":2,"content":"Hello, User!"}

此变化意味着GreetingController中的@RequestParam正如预期一样运行。name指定了默认值为”World”,可以通过请求字符串被明确覆写。

This change demonstrates that the @RequestParam arrangement in GreetingController is working as expected. The name parameter has been given a default value of “World”, but can always be explicitly overridden through the query string.

注意id属性由1变为了2。证明了同一个GreetingController实例承接了多个请求,并且其counter字段也正如预期一样随着每次调用而增加。

Notice also how the id attribute has changed from 1 to 2. This proves that you are working against the same GreetingController instance across multiple requests, and that its counter field is being incremented on each call as expected.

总结

Summary

恭喜!你已经完成了使用Spring来进行RESTful web服务的开发。

Congratulations! You’ve just developed a RESTful web service with Spring.

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