如何构建可重复读取inputStream的request 如何构建可重复读取inputStrea

构建可重复读取inputStream的request
request中inputStream多次读取

原因
解决方法（缓存读取到的数据）
代码

【如何构建可重复读取inputStream的request】
构建可重复读取inputStream的request 我们知道，request的inputStream只能被读取一次，多次读取将报错，那么如何才能重复读取呢？答案之一是：增加缓冲，记录已读取的内容。
代码如下所示：

import lombok.extern.log4j.Log4j2; import org.springframework.mock.web.DelegatingServletInputStream; import javax.servlet.ServletInputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper; import java.io.*; /** * request wrapper: 可重复读取request.getInputStream */@Log4j2public class RepeatedlyReadRequestWrapper extends HttpServletRequestWrapper {private static final int BUFFER_START_POSITION = 0; private static final int CHAR_BUFFER_LENGTH = 1024; /*** input stream 的buffer*/private final String body; /*** @param request {@link javax.servlet.http.HttpServletRequest} object.*/public RepeatedlyReadRequestWrapper(HttpServletRequest request) {super(request); StringBuilder stringBuilder = new StringBuilder(); InputStream inputStream = null; try {inputStream = request.getInputStream(); } catch (IOException e) {log.error("Error reading the request body…", e); }if (inputStream != null) {try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {char[] charBuffer = new char[CHAR_BUFFER_LENGTH]; int bytesRead; while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {stringBuilder.append(charBuffer, BUFFER_START_POSITION, bytesRead); }} catch (IOException e) {log.error("Fail to read input stream",e); }} else {stringBuilder.append(""); }body = stringBuilder.toString(); }@Overridepublic ServletInputStream getInputStream() throws IOException {final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes()); return new DelegatingServletInputStream(byteArrayInputStream); }}

接下来，需要一个对应的Filter.
代码如下所示：

import javax.servlet.*; import javax.servlet.http.HttpServletRequest; import java.io.IOException; public class RepeatlyReadFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {//Do nothing}@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {if (request instanceof HttpServletRequest) {request = new RepeatedlyReadRequestWrapper((HttpServletRequest) request); }chain.doFilter(request, response); }@Overridepublic void destroy() {//Do nothing}}

最后，需要在web.xml中，增加该Filter的配置（略）。

request中inputStream多次读取在使用HTTP协议实现应用间接口通信时，服务端读取客户端请求过来的数据，会用到request.getInputStream()，第一次读取的时候可以读取到数据，但是接下来的读取操作都读取不到数据。

原因
一个InputStream对象在被读取完成后，将无法被再次读取，始终返回-1；
InputStream并没有实现reset方法（可以重置首次读取的位置），无法实现重置操作；

解决方法（缓存读取到的数据）
使用request、session等来缓存读取到的数据,这种方式很容易实现，只要setAttribute和getAttribute就行；
使用HttpServletRequestWrapper来包装HttpServletRequest，在中初始化读取request的InputStream数据，以byte[]形式缓存在其中，然后在Filter中将request转换为包装过的request；

代码
编写rHttpServletRequestWrapper子类，用来处理请求数据

import java.io.BufferedReader; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.nio.charset.Charset; import java.util.Enumeration; import javax.servlet.ReadListener; import javax.servlet.ServletInputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper; import lombok.extern.slf4j.Slf4j; @Slf4jpublic class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper{ private final byte[] body; public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException {super(request); Enumeration e = request.getHeaderNames(); while (e.hasMoreElements()){String name = (String) e.nextElement(); String value = https://www.it610.com/article/request.getHeader(name); log.debug("HttpServletRequest头信息：{}-{}", name, value); }body = HttpHelper.getBodyString(request).getBytes(Charset.forName("UTF-8")); } @Override public BufferedReader getReader() throws IOException {return new BufferedReader(new InputStreamReader(getInputStream())); } @Override public ServletInputStream getInputStream() throws IOException {final ByteArrayInputStream bais = new ByteArrayInputStream(body); return new ServletInputStream(){@Overridepublic boolean isFinished(){return false; }@Overridepublic boolean isReady(){return false; }@Overridepublic void setReadListener(ReadListener listener){}@Overridepublic int read() throws IOException{return bais.read(); }}; } @Override public String getHeader(String name) {return super.getHeader(name); } @Override public Enumeration getHeaderNames() {return super.getHeaderNames(); } @Override public Enumeration getHeaders(String name) {return super.getHeaders(name); }}

调用

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest httpRequest = (HttpServletRequest) request; HttpServletResponse httpResponse = (HttpServletResponse) response; ServletRequest requestWrapper = null; requestWrapper = new BodyReaderHttpServletRequestWrapper(httpRequest); //数据读取处理//...//将requestWrapper专递给后面的过滤器filterChain.doFilter(requestWrapper, httpResponse); }

以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。