@RequestMapping实现rest风格请求

╰半夏微凉° 2022-05-26 06:51 230阅读 0赞

*  概念

Restful就是一个资源定位及资源操作的风格。不是标准也不是协议，只是一种风格。基于这个风格设计的软件可以更简洁，更有层次，更易于实现缓存等机制。

*  资源

资源：互联网所有的事物都可以被抽象为资源  
资源操作：使用POST、DELETE、PUT、GET，使用不同方法对资源进行操作。 分别对应 添加、 删除、修改、查询。  
传统方式操作资源：  
通过不同的参数来实现不同的效果！

> http://127.0.0.1/item/queryItem.action?id=1 查询,GET http://127.0.0.1/item/saveItem.action 新 增,POST http://127.0.0.1/item/updateItem.action 更新,POST http://127.0.0.1/item/deleteItem.action?id=1 删除,GET或POST  
> 使用RESTful操作资源：可以通过不同的请求方式来实现不同的效果！如下：请求地址一样，但是功能可以不同。  
> http://127.0.0.1/item/1 查询,GET  
> http://127.0.0.1/item 新增,POST  
> http://127.0.0.1/item 更新,PUT  
> http://127.0.0.1/item/1 删除,DELETE

**REST：即 Representational State Transfer。**（资源）表现层状态转化。是目前 最流行的一种互联网软件架构。它结构清晰、符合标准、易于理解、扩展方便， 所以正得到越来越多网站的采用

**• 资源（Resources）：**网络上的一个实体，或者说是网络上的一个具体信息。它 可以是一段文本、一张图片、一首歌曲、一种服务，总之就是一个具体的存在。 可以用一个URI（统一资源定位符）指向它，每种资源对应一个特定的 URI 。要 获取这个资源，访问它的URI就可以，因此 URI 即为每一个资源的独一无二的识 别符。

**• 表现层（Representation）：**把资源具体呈现出来的形式，叫做它的表现层 （Representation）。比如，文本可以用 txt 格式表现，也可以用 HTML 格 式、XML 格式、JSON 格式表现，甚至可以采用二进制格式。

**• 状态转化（State Transfer）：**每发出一个请求，就代表了客户端和服务器的一 次交互过程。HTTP协议，是一个无状态协议，即所有的状态都保存在服务器 端。因此，如果客户端想要操作服务器，必须通过某种手段，让服务器端发生“ 状态转化”（State Transfer）。而这种转化是建立在表现层之上的，所以就是 “ 表现层状态转化” 。具体说，就是 HTTP 协议里面，四个表示操作方式的动 词：GET、POST、PUT、DELETE。它们分别对应四种基本操作：GET 用来获 取资源，POST 用来新建资源，PUT 用来更新资源，DELETE 用来删除资源。

### 1）REST具体表现： ###

> \--- /account/1 HTTP GET 获取id=1的account
> 
> \--- /account/1 HTTP DELETE 删除id=1的account
> 
> \--- /aacount/1 HTTP PUT 更新id=1的account
> 
> \--- /account HTTP POST 新增account

***通过 org.springframework.web.filter.HiddenHttpMethodFilter 把 POST 请求转化为 PUT 和 DELETE 请求***

//
    // Source code recreated from a .class file by IntelliJ IDEA
    // (powered by Fernflower decompiler)
    //
     
    package org.springframework.web.filter;
     
    import java.io.IOException;
    import java.util.Arrays;
    import java.util.Collections;
    import java.util.List;
    import java.util.Locale;
    import javax.servlet.FilterChain;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletRequestWrapper;
    import javax.servlet.http.HttpServletResponse;
    import org.springframework.http.HttpMethod;
    import org.springframework.util.Assert;
    import org.springframework.util.StringUtils;
     
    public class HiddenHttpMethodFilter extends OncePerRequestFilter {
        private static final List<String> ALLOWED_METHODS;
        public static final String DEFAULT_METHOD_PARAM = "_method";
        private String methodParam = "_method";
     
        public HiddenHttpMethodFilter() {
        }
     
        public void setMethodParam(String methodParam) {
            Assert.hasText(methodParam, "'methodParam' must not be empty");
            this.methodParam = methodParam;
        }
     
        protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
            HttpServletRequest requestToUse = request;
            if("POST".equals(request.getMethod()) && request.getAttribute("javax.servlet.error.exception") == null) {
                String paramValue = request.getParameter(this.methodParam);
                if(StringUtils.hasLength(paramValue)) {
                    String method = paramValue.toUpperCase(Locale.ENGLISH);
                    if(ALLOWED_METHODS.contains(method)) {
                        requestToUse = new HiddenHttpMethodFilter.HttpMethodRequestWrapper(request, method);
                    }
                }
            }
     
            filterChain.doFilter((ServletRequest)requestToUse, response);
        }
     
        static {
            ALLOWED_METHODS = Collections.unmodifiableList(Arrays.asList(new String[]{HttpMethod.PUT.name(), HttpMethod.DELETE.name(), HttpMethod.PATCH.name()}));
        }
     
        private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {
            private final String method;
     
            public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
                super(request);
                this.method = method;
            }
     
            public String getMethod() {
                return this.method;
            }
        }
    }

从 HiddenHttpMethodFilter 的源码可以看出，Spring 根据请求中的 \_method 参数进行转化，因此如果想发起 REST 风格的 DELETE 或者 PUT 请求，只需要在表单中带上 \_method 参数，并且把 \_method 的值设置为 DELETE 或者 PUT（大写） 即可。详细例子如下：

在 web.xml 中配置 HiddenHttpMethodFilter  
编写 handler 代码  
编写页面  
**1.在 web.xml 中配置 HiddenHttpMethodFilter**

<filter>
    		<filter-name>HiddenHttpMethodFilter</filter-name>
    		<filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
    	</filter>
    	
    	<filter-mapping>
    		<filter-name>HiddenHttpMethodFilter</filter-name>
    		<url-pattern>/*</url-pattern>
    	</filter-mapping>

**2) 编写页面**

<form action="restfulTest/testRest/1" method="post">
             <input type="hidden"  name="_method" value="DELETE"/>
             <input type="submit" value="TestRest DELETE"/>
          </form>
           <br><br>
           
           <form action="restfulTest/testRest/1" method="post">
             <input type="hidden"  name="_method" value="PUT"/>
             <input type="submit" value="TestRest PUT"/>
          </form>
          <br><br>
          
          <form action="restfulTest/testRest" method="post">
            <input type="submit" value="TestRest Post"/>
          </form>
          <br><br>
           <a href="restfulTest/testRest/1">TestRest Get </a>

**3)编写 handler 代码**

@RequestMapping("/restfulTest")
    @Controller
    public class RestTestHandler {
     
    	private static final String SUCCESS="success";
    	/**
    	 * 1. 使用 @RequestMapping 注解来映射请求的 URL
    	 * 2. 返回值会通过视图解析器解析为实际的物理视图, 对于 InternalResourceViewResolver 视图 
         解析器, 会做如下的解析:
    	 * 通过 prefix + returnVal + 后缀 这样的方式得到实际的物理视图, 然会做转发操作
    	 * 
    	 * /WEB-INF/views/success.jsp
    	 * 
    	 * @return
    	 */
    	 @RequestMapping(value="/testRest/{id}",method=RequestMethod.DELETE)
    	   public String testDelete(@PathVariable Integer id){
    		   System.out.println(" TestRest DELETE:"+id);
    		   return SUCCESS;
    	   }
     
    	   @RequestMapping(value="/testRest/{id}",method=RequestMethod.PUT)
    	   public String testPut(@PathVariable Integer id){
    		   System.out.println(" TestRest PUT:"+id);
    		   return SUCCESS;
    	   }
    	   
    	   @RequestMapping(value="/testRest",method=RequestMethod.POST)
    	   public String testPost(){
    		   System.out.println(" TestRest POST:");
    		   return SUCCESS;
    	   }
    	
    	
       @RequestMapping(value="/testRest/{id}",method=RequestMethod.GET)
       public String testRest(@PathVariable Integer id){
    	   System.out.println(" TestRest Get:"+id);
    	   return SUCCESS;
       }
    	
    }

注：handler 中 @RequestParam 注解必须加上 required 参数，否则访问页面会出现400错误

1）、RestfulCRUD：CRUD满足Rest风格；

**URI： /资源名称/资源标识 HTTP请求方式区分对资源CRUD操作**

![70][]

实验具体内容

![70 1][]’

**示例：**  
– /order/1 HTTP GET ：得到 id = 1 的 order  
– /order/1 HTTP DELETE：删除 id = 1的 order  
– /order/1 HTTP PUT：更新id = 1的 order  
– /order HTTP POST：新增 order • HiddenHttpMethodFilter：浏览器 form 表单只支持 GET 与 POST 请求，而DELETE、PUT 等 method 并不支 持，Spring3.0 添加了一个过滤器，可以将这些请求转换 为标准的 http 方法，使得支持 GET、POST、PUT 与 DELETE 请求。

### 2）SpringMVC中如何实现REST？ ###

众所周知，浏览器form表单只支持GET与POST请求，而DELETE、PUT等method并不支持。Spring3.0增加了一个过滤器，可以将这些请求转化为标准的http方法，使得支持GET、POST、PUT及DELETE请求。

这个过滤器就是：org.springframework.web.filter.HiddenHttpMethodFilter

1 package org.springframework.web.filter;
     2 
     3 import java.io.IOException;
     4 import java.util.Locale;
     5 import javax.servlet.FilterChain;
     6 import javax.servlet.ServletException;
     7 import javax.servlet.http.HttpServletRequest;
     8 import javax.servlet.http.HttpServletRequestWrapper;
     9 import javax.servlet.http.HttpServletResponse;
    10 
    11 import org.springframework.util.Assert;
    12 import org.springframework.util.StringUtils;
    13 import org.springframework.web.util.WebUtils;
    14 
    15 /**
    16  * {@link javax.servlet.Filter} that converts posted method parameters into HTTP methods,
    17  * retrievable via {@link HttpServletRequest#getMethod()}. Since browsers currently only
    18  * support GET and POST, a common technique - used by the Prototype library, for instance -
    19  * is to use a normal POST with an additional hidden form field ({@code _method})
    20  * to pass the "real" HTTP method along. This filter reads that parameter and changes
    21  * the {@link HttpServletRequestWrapper#getMethod()} return value accordingly.
    22  *
    23  * <p>The name of the request parameter defaults to {@code _method}, but can be
    24  * adapted via the {@link #setMethodParam(String) methodParam} property.
    25  *
    26  * <p><b>NOTE: This filter needs to run after multipart processing in case of a multipart
    27  * POST request, due to its inherent need for checking a POST body parameter.</b>
    28  * So typically, put a Spring {@link org.springframework.web.multipart.support.MultipartFilter}
    29  * <i>before</i> this HiddenHttpMethodFilter in your {@code web.xml} filter chain.
    30  *
    31  * @author Arjen Poutsma
    32  * @author Juergen Hoeller
    33  * @since 3.0
    34  */
    35 public class HiddenHttpMethodFilter extends OncePerRequestFilter {
    36 
    37     /** Default method parameter: {@code _method} */
    38     public static final String DEFAULT_METHOD_PARAM = "_method";
    39 
    40     private String methodParam = DEFAULT_METHOD_PARAM;
    41 
    42 
    43     /**
    44      * Set the parameter name to look for HTTP methods.
    45      * @see #DEFAULT_METHOD_PARAM
    46      */
    47     public void setMethodParam(String methodParam) {
    48         Assert.hasText(methodParam, "'methodParam' must not be empty");
    49         this.methodParam = methodParam;
    50     }
    51 
    52     @Override
    53     protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
    54             throws ServletException, IOException {
    55 
    56         HttpServletRequest requestToUse = request;
    57 
    58         if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
    59             String paramValue = request.getParameter(this.methodParam);
    60             if (StringUtils.hasLength(paramValue)) {
    61                 requestToUse = new HttpMethodRequestWrapper(request, paramValue);
    62             }
    63         }
    64 
    65         filterChain.doFilter(requestToUse, response);
    66     }
    67 
    68 
    69     /**
    70      * Simple {@link HttpServletRequest} wrapper that returns the supplied method for
    71      * {@link HttpServletRequest#getMethod()}.
    72      */
    73     private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {
    74 
    75         private final String method;
    76 
    77         public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
    78             super(request);
    79             this.method = method.toUpperCase(Locale.ENGLISH);
    80         }
    81 
    82         @Override
    83         public String getMethod() {
    84             return this.method;
    85         }
    86     }
    87 
    88 }从这个filter代码中可以得知，该filter是通过POST方式提交表单，该表单中包含一个名称为_method的隐藏域，该隐藏域的值用来判定将要转化的请求方式。所谓的转化请求方式，就是在该filter中重新生成了一个新的、标准化的请求。

### 3）如何使用到springmvc项目中？ ###

步骤一：在web.xml中添加filter配置：

<filter>
            <filter-name>HiddenHttpMethodFilter</filter-name>
            <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>HiddenHttpMethodFilter</filter-name>
            <url-pattern>/*</url-pattern>
        </filter-mapping>

步骤二：在HelloWord.java中添加get/post/put/delete方法：

1 package com.dx.springlearn.handlers;
     2 
     3 import org.springframework.stereotype.Controller;
     4 import org.springframework.web.bind.annotation.PathVariable;
     5 import org.springframework.web.bind.annotation.RequestMapping;
     6 import org.springframework.web.bind.annotation.RequestMethod;
     7 
     8 @Controller
     9 @RequestMapping("class_requestmapping")
    10 public class HelloWord {
    11     private static String SUCCESS = "success";
    12 
    13     @RequestMapping(value = "/accountDelete/{id}", method = RequestMethod.DELETE)
    14     public String accountDelete(@PathVariable("id") Integer id) {
    15         System.out.println("test rest DELETE,account id:" + id);
    16         return SUCCESS;
    17     }
    18 
    19     @RequestMapping(value = "/accountPut/{id}", method = RequestMethod.PUT)
    20     public String accountPut(@PathVariable("id") Integer id) {
    21         System.out.println("test rest PUT,account id:" + id);
    22         return SUCCESS;
    23     }
    24 
    25     @RequestMapping(value = "/account", method = RequestMethod.POST)
    26     public String account() {
    27         System.out.println("test rest POST");
    28         return SUCCESS;
    29     }
    30 
    31     @RequestMapping(value = "/account/{id}", method = RequestMethod.GET)
    32     public String account(@PathVariable("id") Integer id) {
    33         System.out.println("test rest GET,account id:" + id);
    34         return SUCCESS;
    35     }
    36 }步骤三：在index.jsp中添加get/post/put/delete方法请求的html脚本：

<form id="form_testRestMethod_DELETE" name="form_testRestMethod_DELETE" method="POST"
            action="class_requestmapping/accountDelete/2">
            <input type="hidden" name="_method" value="DELETE" />
            <button name="submit" id="submit">test rest DELETE</button>
        </form>
        <br>
            
        <form id="form_testRestMethod_PUT" name="form_testRestMethod_PUT" method="POST"
            action="class_requestmapping/accountPut/2">
            <input type="hidden" name="_method" value="PUT" />
            <button name="submit" id="submit">test rest PUT</button>
        </form>
        <br>
            
        <form id="form_testRestMethod_POST" name="form_testRestMethod_POST"
            method="POST" action="class_requestmapping/account">
            <button name="submit" id="submit">test rest POST</button>
        </form>
        <br>
            
        <a href="class_requestmapping/account/1">test rest GET</a>
        <br>

步骤四：测试打印结果为：

> test rest GET,account id:1  
> test rest POST  
> test rest PUT,account id:2  
> test rest DELETE,account id:2

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