Beginning Spring学习笔记——第11章 使用Spring开发REST风格的Web服务

REST

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即表述性状态转移（REpresentational State Transfer），是一种基于HTTP的结构原则，一种表示被操作的资源的方法。
REST Web服务完全依赖HTTP方法，每一种方法都会对某一种资源进行操作。GET方法常用来获取某一资源或者资源集合。POST方法则用于创建。PUT方法用于更新。DELETE方法用于从系统中删除资源。

使用REST Web服务进行CRUD操作

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本章所用的依赖文件有：

<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>4.0.0modelVersion>
  <groupId>org.springframework.samples.service.servicegroupId>
  <artifactId>SpringAOPTestartifactId>
  <version>0.0.1-SNAPSHOTversion>
  <packaging>warpackaging>

    <properties>

        
        <java.version>1.6java.version>
        <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>

        
        <jsp.version>2.3.1jsp.version>
        <jstl.version>1.2jstl.version>
        <servlet.version>3.1.0servlet.version>


        
        <spring-framework.version>4.3.10.RELEASEspring-framework.version>

        
        <hibernate.version>5.2.10.Finalhibernate.version>

        
        <logback.version>1.2.3logback.version>
        <slf4j.version>1.7.25slf4j.version>

        
        <junit.version>4.12junit.version>

        
        <aspectj.version>1.8.10aspectj.version>

        
        <jackson.version>2.9.0jackson.version>

    properties>

    <dependencies>

        
        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-webmvcartifactId>
            <version>${spring-framework.version}version>
        dependency>

        
        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>jstlartifactId>
            <version>${jstl.version}version>
        dependency>
        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>javax.servlet-apiartifactId>
            <version>${servlet.version}version>
            <scope>providedscope>
        dependency>
        <dependency>
            <groupId>javax.servlet.jspgroupId>
            <artifactId>javax.servlet.jsp-apiartifactId>
            <version>${jsp.version}version>
            <scope>providedscope>
        dependency>

        
        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-txartifactId>
            <version>${spring-framework.version}version>
        dependency>

        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-aopartifactId>
            <version>${spring-framework.version}version>
        dependency>

        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-coreartifactId>
            <version>${spring-framework.version}version>
        dependency>

        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-beansartifactId>
            <version>${spring-framework.version}version>
        dependency>

        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-contextartifactId>
            <version>${spring-framework.version}version>
        dependency>

        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-webartifactId>
            <version>${spring-framework.version}version>
        dependency>

        
        <dependency>
            <groupId>org.slf4jgroupId>
            <artifactId>slf4j-apiartifactId>
            <version>${slf4j.version}version>
            <scope>compilescope>
        dependency>
        <dependency>
            <groupId>ch.qos.logbackgroupId>
            <artifactId>logback-classicartifactId>
            <version>${logback.version}version>
            <scope>runtimescope>
        dependency>

        
        <dependency>
            <groupId>org.hibernategroupId>
            <artifactId>hibernate-entitymanagerartifactId>
            <version>${hibernate.version}version>
        dependency>


        
        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-testartifactId>
            <version>${spring-framework.version}version>
            <scope>testscope>
        dependency>
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>${junit.version}version>
            <scope>testscope>
        dependency>

        
        <dependency>
            <groupId>org.aspectjgroupId>
            <artifactId>aspectjweaverartifactId>
            <version>${aspectj.version}version>
        dependency>

        
        <dependency>
            <groupId>com.fasterxml.jackson.coregroupId>
            <artifactId>jackson-coreartifactId>
            <version>${jackson.version}version>
        dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.coregroupId>
            <artifactId>jackson-databindartifactId>
            <version>${jackson.version}version>
        dependency>

    dependencies> 
project>

项目目录结构如下：

首先在com.lonelyquantum.wileybookch11.domain包中创建域类User：

public class User {

    private int id;
    private String name;

    public User() {}

    public User(int id, String name){
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

然后去com.lonelyquantum.wileybookch11.repository包中创建文件UserRepository类存储User对象。

@Repository
public class UserRepository {

    private Map users = new HashMap();

    @PostConstruct
    public void setup(){
        users.put(1, new User(1,"Madoka Kaname"));
        users.put(2, new User(2,"Homura Akemi"));
    }

    public void save(User user){
        users.put(user.getId(), user);
    }

    public List findAll(){
        return new ArrayList(users.values());
    }

    public User find(int id){
        return users.get(id);
    }

    public void update(int id, User user){
        users.put(id, user);
    }

    public void delete(int id){
        users.remove(id);
    }
}

该类通过Map来存储Id，UserName对，并提供了CRUD方法。
接下来在com.lonelyquantum.wileybookch11.controller包中创建UserRestController类进行控制。

@RestController
@RequestMapping("/rest")
public class UserRestController {

    @Autowired
    private UserRepository userRepository;

    @RequestMapping(value = "/users", method = RequestMethod.POST)
    public void save(@RequestBody User user){
        userRepository.save(user);
    }

    @RequestMapping(value = "/users", method = RequestMethod.GET)
    public List list(){
        return userRepository.findAll();
    }

    @RequestMapping(value = "/users/{id}", method = RequestMethod.GET)
    public User get(@PathVariable("id") int id){
        User user = userRepository.find(id);
        if(user == null){
            throw new RestException(1, "User not found!", "User with id: " + id + " not found in the system");
        }
        return user;
    }

    @RequestMapping(value = "/users/{id}", method = RequestMethod.PUT)
    public void update(@PathVariable("id") int id, @RequestBody User user){
        userRepository.update(id, user);
    }

    @RequestMapping(value = "/users/{id}", method = RequestMethod.DELETE)
    public ResponseEntity delete(@PathVariable("id") int id){
        userRepository.delete(id);
        return new ResponseEntity(Boolean.TRUE, HttpStatus.OK);
    }
}

该类将Web请求映射到处理方法上。
接着采用springmvc-servlet.xml来配置servlet。

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context-4.0.xsd
                           http://www.springframework.org/schema/mvc
                           http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">

    <context:component-scan base-package="com.lonelyquantum.wileybookch11" />
    <context:annotation-config />

    <mvc:annotation-driven />
beans>

当然，也可以通过在包com.lonelyquantum.wileybookch11.config中创建配置类来配置Servlet：

@Configuration
@ComponentScan(basePackages = {"com.lonelyquantum.wileybookch11"})
@EnableWebMvc
public class AppConfig {

}

然后在web.xml中用URL定义DispatcherServlet：

 <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
      version="3.1">

    <servlet>
        <servlet-name>springmvcservlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class>
        <load-on-startup>1load-on-startup>
    servlet>

    <servlet-mapping>
        <servlet-name>springmvcservlet-name>
        <url-pattern>/*url-pattern>
    servlet-mapping>
web-app>

如果是采用Java配置的servlet则应该在配置中引用AppConfig类。

 <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
          version="3.1">

     <servlet>
         <servlet-name>springmvcservlet-name>
         <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class>
         <init-param>
             <param-name>contextClassparam-name>
             <param-value>
                 org.springframework.web.context.support.AnnotationConfigWebApplicationContext
             param-value>
         init-param>
         <init-param>
             <param-name>contextConfigLocationparam-name>
             <param-value>
                 com.lonelyquantum.wileybookch11.config.AppConfig
             param-value>
         init-param>
         <load-on-startup>1load-on-startup>
     servlet>

     <servlet-mapping>
         <servlet-name>springmvcservlet-name>
         <url-pattern>/*url-pattern>
     servlet-mapping>
 web-app>

将工程部署到Tomcat上运行容器，就可以用SoapUI进行REST调试了。
打开SoapUI后首先File->NEW REST Project

如上填写url。
然后生成如下项目：

之后点击左上角运行图标，将右侧选项卡调整至JSON。可得返回结果：

此处Method为GET，表示采用的是GET方法。在user路径采用该方法返回的是全部用户的User类。
可以右键资源添加新方法以测试其他操作：

我们可以先建立一个名为New User的POST方法来创建新用户：

为了使用这个方法，我们需要输入新用户的参数再执行：

注意输入的数据类型调整正确。左下角会显示相应时间，该方法没有返回值，但是可以再次执行之前的GET方法显示插入的用户。

接下来创建Update方法，采用的是PUT方法，注意，该方法的资源需要指向具体的user，输入类型也应该调整为json。

执行完毕再使用第一个GET方法可以看到user3的内容已经更新：

最后创建DELETE 方法，该方法与UPDATE类似，也需要指定具体user。

执行完毕再用第一个GET方法查看，可发现id=3的user已经被删除。

可以从方法中返回HTTP状态码告知用户方法执行情况。之前delete方法中就返回了return new ResponseEntity(Boolean.TRUE, HttpStatus.OK);表示成功。状态码如下：
1xx 信息
2xx 成功
3xx 重定向
4xx 客户端错误
5xx 服务器错误

使用XML响应的REST Web服务

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刚刚的项目中我们的REST方法返回的都是JSON格式的数据，其实也可以用XML格式返回数据。只要给域类添加如下注解：

@XmlRootElement
public class User {

    @XmlElement
    private int id;
    @XmlElement
    private String name;

    public User() {}

    public User(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

就可以在查找某个user时返回XML格式的输出

使用异常处理机制

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先在com.lonelyquantum.wileybookch11.domain创建RestErrorMessage类来表示异常信息。

public class RestErrorMessage {

    private HttpStatus status;
    private int code;
    private String message;
    private String detailedMessage;
    private String exceptionMessage;

    public RestErrorMessage(HttpStatus status, int code, String message, String detailedMessage,
            String exceptionMessage) {
        super();
        this.status = status;
        this.code = code;
        this.message = message;
        this.detailedMessage = detailedMessage;
        this.exceptionMessage = exceptionMessage;
    }

    public int getCode() {
        return code;
    }

    public String getMessage() {
        return message;
    }

    public String getDetailedMessage() {
        return detailedMessage;
    }

    public String getExceptionMessage() {
        return exceptionMessage;
    }

}

在该项目中创建com.lonelyquantum.wileybookch11.exception包来保存抛出的异常

public class RestException extends RuntimeException{

    private int code;
    private String message;
    private String detailedMessage;

    public RestException(int code, String message, String detailedMessage){
        this.code = code;
        this.message = message;
        this.detailedMessage = detailedMessage;
    }

    public int getCode() {
        return code;
    }

    @Override
    public String getMessage() {
        // TODO Auto-generated method stub
        return super.getMessage();
    }

    public String getDetailedMessage() {
        return detailedMessage;
    }
}

以及com.lonelyquantum.wileybookch11.handler包来保存处理异常的方法。

@ControllerAdvice
public class RestExceptionHandler extends ResponseEntityExceptionHandler{

    @ExceptionHandler(Exception.class)
    protected ResponseEntity