如何重复读取HttpServletRequest的HTTP请求体数据
原创如何重复读取HttpServletRequest的HTTP请求体数据
原创
在开发Java web项目的时候，经常会用到Spring MVC的注解@RequestBody，用于读取HTTP请求体。有时候又要在业务代码里面读取HTTP请求体。有时候又需要一些拦截器或过滤器，比如，根据请求体中的数据，判断该用户有没有权限处理该数据，这时候拦截器也需要读取HTTP请求体。如果你同时遇到这些场景，你就会发现会报错。什么原因呢？因为所有读取HTTP请求体的操作，最终都要调用HttpServletRequest的getInputStream()方法和getReader()方法，而这两个方法总共只能被调用一次，第二次调用就会报错，原因是数据是从网络字节流里面读取的，字节流被读了一次之后，就没有数据了。那么如何重复读取HttpServletRequest携带的HTTP请求体数据呢？
其实思路很简单：第一步，读取HttpServletRequest的字节流的数据，保存到一个字节数组bytes；第二步，重写getInputStream()方法和getReader()方法，让这两个方法都从字节数组bytes中读取数据，返回给调用者；第三步，写个过滤器，让HTTP请求一进入系统，就执行第一步和第二步，然后后面都用重写的HttpServletRequest对象。这样，就可以重复读取HttpServletRequest携带的HTTP请求体数据了。
本文代码案例都是基于Servlet3.0写的，之前的版本和之后的版本实现方法都有可能不同。
1.读取字节流数据到字节数组
写一个HttpServletRequestWrapper的扩展类RepeatableHttpServletRequest，然后在构造方法中把字节流中的数据保存到字节数组中。
public class RepeatableHttpServletRequest extends HttpServletRequestWrapper {
private final byte[] bytes;
public RepeatableHttpServletRequest(HttpServletRequest request) throws IOException {
super(request);
bytes = IOUtils.toByteArray(request.getInputStream());
}
}2.重写getInputStream()方法和getReader()方法
重写getInputStream()方法和getReader()方法，让这两个方法都从字节数组bytes中读取数据。这样RepeatableHttpServletRequest就是一个可重复读取的HttpServletRequest了。
import org.apache.commons.io.IOUtils;
import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
public class RepeatableHttpServletRequest extends HttpServletRequestWrapper {
private final byte[] bytes;
public RepeatableHttpServletRequest(HttpServletRequest request) throws IOException {
super(request);
bytes = IOUtils.toByteArray(request.getInputStream());
}
@Override
public ServletInputStream getInputStream() throws IOException {
return new ServletInputStream() {
private int lastIndexRetrieved = -1;
private ReadListener readListener = null;
@Override
public boolean isFinished() {
return (lastIndexRetrieved == bytes.length-1);
}
@Override
public boolean isReady() {
// This implementation will never block
// We also never need to call the readListener from this method, as this method will never return false
return isFinished();
}
@Override
public void setReadListener(ReadListener readListener) {
this.readListener = readListener;
if (!isFinished()) {
try {
readListener.onDataAvailable();
} catch (IOException e) {
readListener.onError(e);
}
} else {
try {
readListener.onAllDataRead();
} catch (IOException e) {
readListener.onError(e);
}
}
}
@Override
public int read() throws IOException {
int i;
if (!isFinished()) {
i = bytes[lastIndexRetrieved+1];
lastIndexRetrieved++;
if (isFinished() && (readListener != null)) {
try {
readListener.onAllDataRead();
} catch (IOException ex) {
readListener.onError(ex);
throw ex;
}
}
return i;
} else {
return -1;
}
}
};
}
@Override
public BufferedReader getReader() throws IOException {
ByteArrayInputStream is = new ByteArrayInputStream(bytes);
BufferedReader temp = new BufferedReader(new InputStreamReader(is));
return temp;
}
}3.写过滤器，把HttpServletRequest替换成RepeatableHttpServletRequest
过滤器很简单，就是把HttpServletRequest包装成RepeatableHttpServletRequest，然后丢给后面的调用链。
import lombok.extern.slf4j.Slf4j;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@Slf4j
public class RepeatableFilter implements Filter {
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest httpServletRequest = new RepeatableHttpServletRequest((HttpServletRequest)servletRequest);
HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
filterChain.doFilter(httpServletRequest,httpServletResponse);
}
}然后利用过滤器配置，把RepeatableFilter设置成第一个调用的过滤器。注意FilterRegistrationBean的setOrder()方法，数值越小越先执行。
package com.leaforbook.common.configuration;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import javax.servlet.Filter;
@Configuration
public class FilterRegistrationConfiguration {
@Bean
public FilterRegistrationBean someFilterRegistration() {
FilterRegistrationBean registration = new FilterRegistrationBean();
registration.setFilter(repeatableFilter());
registration.addUrlPatterns("/*");
registration.setName("repeatableFilter");
registration.setOrder(1);
return registration;
}
@Bean
public Filter repeatableFilter() {
return new repeatableFilter();
}
}到现在为止，HttpServletRequest就可以随意地读取多次了，要实现一些无业务侵入的功能也容易多了。至于这些功能怎么实现，超出本文范畴，不做讨论。
原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。
如有侵权，请联系 cloudcommunity@tencent.com 删除。
原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。
如有侵权，请联系 cloudcommunity@tencent.com 删除。