如何构建可重复读取inputStream的request

如何构建可重复读取inputStream的request

目录构建可重复读取inputStream的requestrequest中inputStream多次读取原因解决方法（缓存读取到的数据）代码

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ZiHCHTbEe重复读取request.getInputStream

*/

@Log4j2

public 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();

}

@Override

public 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 {

@Override

public void init(FilterConfig filterConfig) throws ServletException {

//Do nothing

}

@Override

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

if (request instanceof HttpServletRequest) {

request = new RepeatedlyReadRequestWrapper((HttpServletRequest) request);

}

chain.doFilter(request, response);

}

@Override

public 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;

@Slf4j

public 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 = 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(){

@Override

public boolean isFinished()

{

return false;

}

@Override

public boolean isReady()

{

return false;

}

@Override

public void setReadListener(ReadListener listener)

{

}

@Override

public int read() throws IOException

{

return bais.read();

http://}

};

}

@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 = nhttp://ull;

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);

}

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