157_SpringBoot_web请求参数处理

1 rest使用与原理
@xxxMapping；
Rest风格支持（使用HTTP请求方式动词来表示对资源的操作）
以前：/getUser获取用户     /deleteUser删除用户    /editUser修改用户 /saveUser保存用户
现在： /user GET-获取用户  DELETE-删除用户 PUT-修改用户  POST-保存用户
核心Filter；HiddenHttpMethodFilter
用法： 表单method=post，隐藏域 _method=put

index表单

      测试REST风格；
        <form action="/user" method="get">
            <input value="REST-GET 提交" type="submit"/>
        </form>
        <form action="/user" method="post">
            <input value="REST-POST 提交" type="submit"/>
        </form>
        <form action="/user" method="post">
            <input name="_method" type="hidden" value="delete"/>
            <input name="_m" type="hidden" value="delete"/>
            <input value="REST-DELETE 提交" type="submit"/>
        </form>
        <form action="/user" method="post">
            <input name="_method" type="hidden" value="PUT"/>
            <input value="REST-PUT 提交" type="submit"/>
        </form>

controller

@RestController
public class HelloController {
    
    //    @RequestMapping(value = "/user",method = RequestMethod.GET)
    @GetMapping("/user")
    public String getUser(){

        return "GET-alex";
    }

    //    @RequestMapping(value = "/user",method = RequestMethod.POST)
    @PostMapping("/user")
    public String saveUser(){
        return "POST-alex";
    }


    //    @RequestMapping(value = "/user",method = RequestMethod.PUT)
    @PutMapping("/user")
    public String putUser(){

        return "PUT-alex";
    }

    @DeleteMapping("/user")
//    @RequestMapping(value = "/user",method = RequestMethod.DELETE)
    public String deleteUser(){
        return "DELETE-alex";
    }
}

SpringBoot中手动开启 (扩展：如何把_method 这个名字换成自定义名字)

@Configuration(proxyBeanMethods = false)
public class WebConfig {
    @Bean
    public HiddenHttpMethodFilter hiddenHttpMethodFilter(){
        HiddenHttpMethodFilter methodFilter = new HiddenHttpMethodFilter();
        methodFilter.setMethodParam("_m");
        return methodFilter;
    }

}

Rest原理（表单提交要使用REST的时候）
表单提交会带上_method=PUT
请求过来被HiddenHttpMethodFilter拦截
请求是否正常，并且是POST
获取到_method的值。
兼容以下请求；PUT.DELETE.PATCH
原生request（post），包装模式requesWrapper重写了getMethod方法，返回的是传入的值。
过滤器链放行的时候用wrapper。以后的方法调用getMethod是调用requesWrapper的。

   @Bean
    @ConditionalOnMissingBean({HiddenHttpMethodFilter.class})
    @ConditionalOnProperty(
        prefix = "spring.mvc.hiddenmethod.filter",
        name = {"enabled"}
    )
    public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
        return new OrderedHiddenHttpMethodFilter();
    }

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);
    }

Rest使用客户端工具，如PostMan直接发送Put、delete等方式请求，无需Filter