Spring Boot框架中在Controller方法里获取Request和Response对象的2种方式

写在前面

javax.servlet.ServletRequest和javax.servlet.ServletResponse都是Servlet容器中定义的接口，分别用于获取客户端请求信息和将响应消息发送给客户端。
有两种方法在Contoller方法中获取它们：

1. 直接在Controller方法参数中声明
2. 通过工具类org.springframework.web.context.request.RequestContextHolder获取

实际的对象实例类跟具体的Servlet容器有关：

• 如果Servlet容器为Tomcat，javax.servlet.ServletRequest实现类为org.apache.catalina.connector.RequestFacade，javax.servlet.ServletResponse实现类为org.apache.catalina.connector.ResponseFacade
• 如果Servlet容器为Undertow，javax.servlet.ServletRequest实现类为io.undertow.servlet.spec.HttpServletRequestImpl，javax.servlet.ServletResponse实现类为io.undertow.servlet.spec.HttpServletResponseImpl

在Controller方法参数中声明

可以直接在Controller方法参数中声明javax.servlet.ServletRequest和javax.servlet.ServletResponse对象，如下示例：

@GetMapping("/hello")
public String request(HttpServletRequest req, HttpServletResponse resp) {System.out.println("req: " + req);System.out.println("resp: " + resp);return "Success";
}

之所以能直接在Controller方法参数中声明javax.servlet.ServletRequest和javax.servlet.ServletResponse对象，实际上是在org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues()方法中进行了解析处理，如下：

// org.springframework.web.method.support.InvocableHandlerMethod
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);args[i] = resolveProvidedArgument(parameter, providedArgs);if (args[i] != null) {continue;}if (this.argumentResolvers.supportsParameter(parameter)) { // 判断是否为支持解析的参数类型try {args[i] = this.argumentResolvers.resolveArgument( // 解析参数对象parameter, mavContainer, request, this.dataBinderFactory);continue;}catch (Exception ex) {if (logger.isDebugEnabled()) {logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);}throw ex;}}if (args[i] == null) {throw new IllegalStateException("Could not resolve method parameter at index " +parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() +": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));}}return args;
}

最终通过org.springframework.web.servlet.mvc.method.annotation.ServletRequestMethodArgumentResolver.resolveArgument()方法解析获取到具体对象。

通过RequestContextHolder工具类获取

在使用Spring Boot框架时，除了可以直接在Controller方法参数中声明javax.servlet.ServletRequest和javax.servlet.ServletResponse对象，还可以通过工具类org.springframework.web.context.request.RequestContextHolder获取，如下示例：

@GetMapping("/hello")
public String hello() {RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();if (requestAttributes != null && requestAttributes instanceof ServletRequestAttributes) {ServletRequestAttributes httpRequestAttributes = (ServletRequestAttributes) requestAttributes;HttpServletRequest req = httpRequestAttributes.getRequest();HttpServletResponse resp = httpRequestAttributes.getResponse();System.out.println("req: " + req);System.out.println("resp: " + resp);}return "Success";
}

之所以可以通过RequestContextHolder工具类获取javax.servlet.ServletRequest和javax.servlet.ServletResponse对象，是因为在org.springframework.web.servlet.FrameworkServlet.processRequest()方法中进行了注入。

// org.springframework.web.servlet.FrameworkServletprotected final void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// 省略其他代码...// 在工具类RequestContextHolder中注入ServletRequest和ServletResponse对象initContextHolders(request, localeContext, requestAttributes);// 省略其他代码...
}

【参考】
Spring——Web作用域：RequestContextListener
springboot 整合 ServletRequestListener监听器