5.如何断点springboot(springmvc)如何解析参数

我这边用一个get请求来示例。这东西知道在哪断点查看，以后遇到问题可以快速定位。

我这里的接口是 http://localhost:8082/pathVariable2/2

  @GetMapping("/pathVariable2/{id}")
  public String pathVariable2(@PathVariable(value = "id")
      String id){
    return id;
  }

1.入口是httpservlet,然后到org.springframework.web.servlet.dispatcherServlet#dodispatch打断点

2.这里2个关键方法

第一是获取适配器

第二个真正用适配器解析参数

2.1适配器一共4个，一般的请求用第一个就好

2.2执行参数解析

1）org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal 一路走下去

2）org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#invokeHandlerMethod 一路走下去

520：这里是拿到所有的参数解析器：最终是遍历所有的参数解析器去解析参数的

0 = {RequestParamMethodArgumentResolver@6898}
1 = {RequestParamMapMethodArgumentResolver@6899}
2 = {PathVariableMethodArgumentResolver@6900}
3 = {PathVariableMapMethodArgumentResolver@6901}
4 = {MatrixVariableMethodArgumentResolver@6902}
5 = {MatrixVariableMapMethodArgumentResolver@6903}
6 = {ServletmodelattributeMethodProcessor@6904}
7 = {RequestResponseBodyMethodProcessor@6905}
8 = {RequestPartMethodArgumentResolver@6906}
9 = {RequestHeaderMethodArgumentResolver@6907}
10 = {RequestHeaderMapMethodArgumentResolver@6908}
11 = {ServletCookieValueMethodArgumentResolver@6909}
12 = {ExpressionValueMethodArgumentResolver@6910}
13 = {SessionAttributeMethodArgumentResolver@6911}
14 = {RequestAttributeMethodArgumentResolver@6912}
15 = {ServletRequestMethodArgumentResolver@6913}
16 = {ServletResponseMethodArgumentResolver@6914}
17 = {httpentityMethodProcessor@6915}
18 = {RedirectAttributesMethodArgumentResolver@6916}
19 = {ModelMethodProcessor@6917}
20 = {MapMethodProcessor@6918}
21 = {ErrorsMethodArgumentResolver@6919}
22 = {SessionStatusMethodArgumentResolver@6920}
23 = {UriComponentsBuilderMethodArgumentResolver@6921}
24 = {PrincipalMethodArgumentResolver@6922}
25 = {RequestParamMethodArgumentResolver@6923}
26 = {ServletmodelattributeMethodProcessor@6924}

所以可以分析的出，我这个接口用PathVariableMethodArgumentResolver来解析，这是后话，肯定是哪所有解析器一个个去解析的。

524：拿到所有的返回值处理器

0 = {ModelAndViewMethodReturnValueHandler@6340}
1 = {ModelMethodProcessor@6341}
2 = {ViewMethodReturnValueHandler@6342}
3 = {ResponseBodyEmitterReturnValueHandler@6343}
4 = {streamingresponsebodyReturnValueHandler@6344}
5 = {httpentityMethodProcessor@6345}
6 = {HttpHeadersReturnValueHandler@6346}
7 = {CallableMethodReturnValueHandler@6347}
8 = {DeferredResultMethodReturnValueHandler@6348}
9 = {AsyncTaskMethodReturnValueHandler@6349}
10 = {ServletmodelattributeMethodProcessor@6350}
11 = {RequestResponseBodyMethodProcessor@6351}
12 = {ViewNameMethodReturnValueHandler@6352}
13 = {MapMethodProcessor@6353}
14 = {ServletmodelattributeMethodProcessor@6354}

3）继续断点，核心执行解析是553行

4）org.springframework.web.servlet.mvc.method.annotation.ServletinvocableHandlerMethod#invokeAndHandle

52行真正执行目标方法，我们进去

5）继续断点org.springframework.web.method.support.invocableHandlerMethod#invokeForRequest

56行获取参数 61行反射执行方法。所以我们得进入56行

6）org.springframework.web.method.support.invocableHandlerMethod#getmethodArgumentValues 方法

protected Object[] getmethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
    //这里拿的是这个方法（到这步已经确认调用哪个方法了）所有参数，遍历去给它们设置值
    MethodParameter[] parameters = this.getmethodParameters();
    if (ObjectUtils.isEmpty(parameters)) {
      return EMPTY_ARGS;
    } else {
      Object[] args = new Object[parameters.length];

      for(int i = 0; i < parameters.length; ++i) {
        MethodParameter parameter = parameters[i];
        parameter.initParameterNamediscovery(this.parameterNamediscoverer);
        args[i] = findProvidedArgument(parameter, providedArgs);
        if (args[i] == null) {
          //判断参数解析器是否支持这种参数解析
          if (!this.resolvers.supportsParameter(parameter)) {
            throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
          }

          try {
            //真正去给参数设置值
            args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
          } catch (Exception var10) {
            if (logger.isDebugEnabled()) {
              String exmsg = var10.getMessage();
              if (exmsg != null && !exmsg.contains(parameter.getExecutable().toGenericString())) {
                logger.debug(formatArgumentError(parameter, exmsg));
              }
            }

            throw var10;
          }
        }
      }

      return args;
    }
  }

6-1）判断参数解析器是否支持这种参数解析

遍历27个参数解析器，看看哪个支持。然后break掉

最终发现是PathVariableMethodArgumentResolver支持

org.springframework.web.servlet.mvc.method.annotation.PathVariableMethodArgumentResolver#supportsParameter

  public boolean supportsParameter(MethodParameter parameter) {
    //不是PathVariable注解的不行
    if (!parameter.hasParameterannotation(PathVariable.class)) {
      return false;
     //不是map开头的可以
    } else if (!Map.class.isAssignableFrom(parameter.nestedIfOptional().getnestedParameterType())) {
      return true;
     //其他情况的考虑
    } else {
      PathVariable pathVariable = (PathVariable)parameter.getParameterannotation(PathVariable.class);
      return pathVariable != null && StringUtils.hasText(pathVariable.value());
    }
  }

6-2）真正去解析参数的值

  @Nullable
  public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
    //获取参数解析器
    HandlerMethodArgumentResolver resolver = this.getArgumentResolver(parameter);
    if (resolver == null) {
      throw new IllegalArgumentException("Unsupported parameter type [" + parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
    } else {
      return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
    }
  }

  public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
    //获取参数对象
    AbstractNamedValueMethodArgumentResolver.NamedValueInfo namedValueInfo = this.getNamedValueInfo(parameter);
    //确认需要解析的参数名字
    MethodParameter nestedParameter = parameter.nestedIfOptional();
    Object resolvedname = this.resolveEmbeddedValuesAndExpressions(namedValueInfo.name);
    if (resolvedname == null) {
      throw new IllegalArgumentException("Specified name must not resolve to null: [" + namedValueInfo.name + "]");
    } else {
      //真正去解析参数的值
      Object arg = this.resolveName(resolvedname.toString(), nestedParameter, webRequest);

类名是:PathVariableMethodArgumentResolver 通过它来解析

uriTemplateVars是请求头带过来的值id=2

这样最终得到参数的值是2

5.如何断点springboot(springmvc)如何解析参数

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