SpringMVC 中获得 request 和 response

request/response 简介

• request 和 response 是对应一次Http通信中的request请求和response返回结果
• Java 的Servlet 协议将其分别封装为 HttpServletRequest 和 HttpServletResponse
• 从中可以获得原始 Http 请求的详细信息，也可控制response操作
• 屏蔽了直接操作底层 Http 的复杂性

方法一

在 Controller 层获取

直接在 controller 的方法参数中加入HttpServletRequest 和 HttpServletResponse 对象参数

@RestController
public class AppController {
    
    @RequestMapping("/test")
    public String getSth(HttpServletRequest request, HttpServletResponse response) {
        ......
    }
}

原理

• spring 会使用反射将这两个属性从上下文环境中注入到对应方法中（使用反射技术对相应的参数做到参数注入）
• 简单理解：读参数->搜索上下文中bean->若匹配上->注入
• 详细代码

第一段

//step1-invokeForRequest()
public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
        //获取 方法参数
        Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs);
        if(this.logger.isTraceEnabled()) {
            StringBuilder returnValue = new StringBuilder("Invoking [");
            returnValue.append(this.getBeanType().getSimpleName()).append(".");
            returnValue.append(this.getMethod().getName()).append("] method with arguments ");
            returnValue.append(Arrays.asList(args));
            this.logger.trace(returnValue.toString());
        }

        Object returnValue1 = this.doInvoke(args);
        if(this.logger.isTraceEnabled()) {
            this.logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue1 + "]");
        }

        return returnValue1;
    }

第二段

    /**
     * Get the method argument values for the current request.
     */
    private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,
            Object... providedArgs) throws Exception {

        MethodParameter[] parameters = getMethodParameters();
        Object[] args = new Object[parameters.length];
        for (int i = 0; i < parameters.length; i++) {
            MethodParameter parameter = parameters[i];
            parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
            GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());
            args[i] = resolveProvidedArgument(parameter, providedArgs);
            if (args[i] != null) {
                continue;
            }
            if (this.argumentResolvers.supportsParameter(parameter)) {
                try {
                    args[i] = this.argumentResolvers.resolveArgument(
                            parameter, mavContainer, request, this.dataBinderFactory);
                    continue;
                }
                catch (Exception ex) {
                    if (logger.isDebugEnabled()) {
                        logger.debug(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);
                    }
                    throw ex;
                }
            }
            if (args[i] == null) {
                String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);
                throw new IllegalStateException(msg);
            }
        }
        return args;
    }

第三段

    /**
     * Attempt to resolve a method parameter from the list of provided argument values.
     */
    private Object resolveProvidedArgument(MethodParameter parameter, Object... providedArgs) {
        if (providedArgs == null) {
            return null;
        }
        for (Object providedArg : providedArgs) {
            if (parameter.getParameterType().isInstance(providedArg)) {
                return providedArg;
            }
        }
        return null;
    }

如果参数类型和提供的参数类型可以匹配，则直接返回。至此，我们分析完了从源码级别分析了，如何做的参数注入。
参考：https://www.jianshu.com/p/0ba4c65e493c

方法二

在非Controller层获得

HttpServletRequest request = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest();

HttpServletResponse response = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getResponse();

HttpServletResponse response = ((ServletWebRequest)RequestContextHolder.getRequestAttributes()).getResponse();

ServletContext context = ContextLoader.getCurrentWebApplicationContext().getServletContext();