最近有一个需要从拦截器中获取post请求的参数的需求，这里记录一下处理过程中出现的问题。

首先想到的就是request.getParameter(String )方法，但是这个方法只能在get请求中取到参数，post是不行的，后来想到了使用流的方式，调用request.getInputStream()获取流，然后从流中读取参数，如下代码所示：

String body = "";

StringBuilder stringBuilder = new StringBuilder();

BufferedReader bufferedReader = null;

InputStream inputStream = null;

try {

inputStream = request.getInputStream();

if (inputStream != null) {

bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

char[] charBuffer = new char[128];

int bytesRead = -1;

while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {

stringBuilder.append(charBuffer, 0, bytesRead);

}

} else {

stringBuilder.append("");

}

} catch (IOException ex) {

e.printStackTrace();

} finally {

if (inputStream != null) {

try {

inputStream.close();

}

catch (IOException e) {

e.printStackTrace();

}

}

if (bufferedReader != null) {

try {

bufferedReader.close();

}

catch (IOException e) {

e.printStackTrace();

}

}

}

body = stringBuilder.toString();

代码中的body就是request中的参数，我这里传的是JSON数据：{"page": 1, "pageSize": 10}，那么body就是：body = "{"page": 1, "pageSize": 10}"，一个JSON字符串。这样是可以成功获取到post请求的body，但是，经过拦截器后，参数经过@RequestBody注解赋值给controller中的方法的时候，却抛出了一个这样的异常：

org.springframework.http.converter.HttpMessageNotReadableException: Required request body is missing

在网上查找资料后发现，request的输入流只能读取一次，那么这是为什么呢？下面是答案：

那是因为流对应的是数据，数据放在内存中，有的是部分放在内存中。read 一次标记一次当前位置(mark position)，第二次read就从标记位置继续读(从内存中copy)数据。 所以这就是为什么读了一次第二次是空了。 怎么让它不为空呢？只要inputstream 中的pos 变成0就可以重写读取当前内存中的数据。javaAPI中有一个方法public void reset() 这个方法就是可以重置pos为起始位置，但是不是所有的IO读取流都可以调用该方法！ServletInputStream是不能调用reset方法，这就导致了只能调用一次getInputStream()。

那么有什么办法可以用户解决呢？上面这篇博客中提到了解决方案，就是重写HttpServletRequestWrapper把request保存下来，然后通过过滤器把保存下来的request再填充进去，这样就可以多次读取request了。步骤如下所示：

①写一个类，继承HttpServletRequestWrapper

import javax.servlet.ReadListener;

import javax.servlet.ServletInputStream;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletRequestWrapper;

import java.io.*;

public class RequestWrapper extends HttpServletRequestWrapper {

private final String body;

public RequestWrapper(HttpServletRequest request) {

super(request);

StringBuilder stringBuilder = new StringBuilder();

BufferedReader bufferedReader = null;

InputStream inputStream = null;

try {

inputStream = request.getInputStream();

if (inputStream != null) {

bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

char[] charBuffer = new char[128];

int bytesRead = -1;

while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {

stringBuilder.append(charBuffer, 0, bytesRead);

}

} else {

stringBuilder.append("");

}

} catch (IOException ex) {

} finally {

if (inputStream != null) {

try {

inputStream.close();

}

catch (IOException e) {

e.printStackTrace();

}

}

if (bufferedReader != null) {

try {

bufferedReader.close();

}

catch (IOException e) {

e.printStackTrace();

}

}

}

body = stringBuilder.toString();

}

@Override

public ServletInputStream getInputStream() throws IOException {

final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());

ServletInputStream servletInputStream = new ServletInputStream() {

@Override

public boolean isFinished() {

return false;

}

@Override

public boolean isReady() {

return false;

}

@Override

public void setReadListener(ReadListener readListener) {

}

@Override

public int read() throws IOException {

return byteArrayInputStream.read();

}

};

return servletInputStream;

}

@Override

public BufferedReader getReader() throws IOException {

return new BufferedReader(new InputStreamReader(this.getInputStream()));

}

public String getBody() {

return this.body;

}

}

②拦截器层面

package com.miniprogram.web.douyin.interceptor;

import com.alibaba.fastjson.JSON;

import com.miniprogram.api.douyin.user.req.DyuserReq;

import com.miniprogram.common.auth.VisitLimitCount;

import com.miniprogram.common.cache.RedisCache;

import com.miniprogram.common.config.InterceptorConfigMap;

import com.miniprogram.common.config.InterceptorUrlConfig;

import com.miniprogram.common.douyin.SearchEngineMapConstants;

import com.miniprogram.common.response.Response;

import com.miniprogram.common.session.*;

import com.miniprogram.common.utils.DateUtil;

import com.miniprogram.dao.common.UserLoginEntity.Users;

import com.miniprogram.service.douyin.users.UsersService;

import com.miniprogram.web.douyin.config.RequestWrapper;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.beans.BeanUtils;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

import org.springframework.web.servlet.ModelAndView;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

@Component("authSecurityInterceptor")

public class AuthSecurityInterceptor extends HandlerInterceptorAdapter {

private Logger logger = LoggerFactory.getLogger(AuthSecurityInterceptor.class);

@Autowired

private UsersService douYinUsersService;

@Autowired

private RedisCache redisCache;

@Autowired

private VisitLimitCount visitLimitCount;

@Override

public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {

try {

RequestWrapper requestWrapper = new RequestWrapper(httpServletRequest);

String body = requestWrapper.getBody();

System.out.println(body);

return true;

}catch (Exception e){

logger.error("权限判断出错",e);

}

return false;

}

@Override

public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

}

@Override

public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

}

}

③过滤器Filter，用来把request传递下去

import com.miniprogram.web.douyin.config.RequestWrapper;

import javax.servlet.*;

import javax.servlet.annotation.WebFilter;

import javax.servlet.http.HttpServletRequest;

import java.io.IOException;

@Component

@WebFilter(urlPatterns = "/*",filterName = "channelFilter")

public class ChannelFilter implements Filter {

@Override

public void init(FilterConfig filterConfig) throws ServletException {

}

@Override

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

ServletRequest requestWrapper = null;

if(servletRequest instanceof HttpServletRequest) {

requestWrapper = new RequestWrapper((HttpServletRequest) servletRequest);

}

if(requestWrapper == null) {

filterChain.doFilter(servletRequest, servletResponse);

} else {

filterChain.doFilter(requestWrapper, servletResponse);

}

}

@Override

public void destroy() {

}

}

④在启动类中注册拦截器

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.boot.web.servlet.MultipartConfigFactory;

import org.springframework.boot.web.servlet.ServletComponentScan;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.ComponentScan;

import org.springframework.context.annotation.Configuration;

@SpringBootApplication

@ServletComponentScan //注册过滤器注解

@Configuration

public class WebApplication {

public static void main(String[] args) {

SpringApplication.run(WebApplication.class, args);

}

}

经测试，问题解决