springmvc基础知识（14）：springmvc对rest的支持(rest风格的CRUD)

配置过滤器： HiddenHttpMethodFilter

<filter>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <!-- 注意这里 -->
    <url-pattern>/*</url-pattern>
</filter-mapping>

配置这个是为了细分POST请求，常用的有POST、PUT、DELETE等。

看下源码：

public class HiddenHttpMethodFilter extends OncePerRequestFilter {

    /** Default method parameter: {@code _method} */
    public static final String DEFAULT_METHOD_PARAM = "_method";

    private String methodParam = DEFAULT_METHOD_PARAM;


    /**
     * Set the parameter name to look for HTTP methods.
     * @see #DEFAULT_METHOD_PARAM
     */
    public void setMethodParam(String methodParam) {
        Assert.hasText(methodParam, "'methodParam' must not be empty");
        this.methodParam = methodParam;
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        String paramValue = request.getParameter(this.methodParam);
        if ("POST".equals(request.getMethod()) && StringUtils.hasLength(paramValue)) {
            String method = paramValue.toUpperCase(Locale.ENGLISH);
            HttpServletRequest wrapper = new HttpMethodRequestWrapper(request, method);
            filterChain.doFilter(wrapper, response);
        }
        else {
            filterChain.doFilter(request, response);
        }
    }

可以看到这个过滤器过滤请求,获取name=’_method’携带的数据,一般这个是前台表单提交的细分的POST，比如PUT或者DELETE。过滤器将拦截到的HTTP的method修改为获取的_method值。

• 前台:

<form action="book" method="get">
    <button type="submit">查询</button>
</form>
<form action="book" method="post">
    <button type="submit">新增</button>
</form>
<form action="book/123" method="post">
    <input type="hidden" name="_method" value="PUT">
    <button type="submit">修改</button>
</form>
<form action="book/123" method="post">
    <input type="hidden" name="_method" value="DELETE">
    <button type="submit">删除</button>
</form>

表单里定义一个name=”_method” 的隐藏域,主要是给上面配置的过滤器设置细分的POST请求的method值。

• 后台

@RequestMapping(value = "/book",method = RequestMethod.GET)
public String getBook(){
    System.out.println("查询书籍...");
    return "success";
}

@RequestMapping(value = "/book",method = RequestMethod.POST)
public String addBook(){
    System.out.println("新增书籍...");
    return "success";
}

@RequestMapping(value = "/book/{id}",method = RequestMethod.DELETE)
public String deleteBook(@PathVariable("id") String id){
    System.out.println("删除书籍,ID为["+id+"]...");
    return "success";
}

@RequestMapping(value = "/book/{id}",method = RequestMethod.PUT)
public String updateBook(@PathVariable("id") String id){
    System.out.println("修改书籍,ID为["+id+"]...");
    return "success";
}

• /book/{id} 中的id是占位符,用于接收前台传过来的数据,使用@PathVariable(“id”)可以将之绑定到方法参数上。
• 可以看到，这一组的增删改查的请求URL是统一的,通过请求的method值进行区分。