Method of repeatedly reading InputStream in HttpServletRequest

CG Guobin 2020-11-12 22:34:41
method repeatedly reading inputstream httpservletrequest


The first sentence of the opening , Have you ever encountered such a problem :

  • adopt httpServletRequest.getInputStream() obtain InputStream after , encounter Required request body is missing error ?

If you answer “ yes ” Words , Then you're right . In this paper , Let's talk about ,

  • problem 1: Why? InputStream Can't read repeatedly ?
  • problem 2: How to read repeatedly HttpServletRequest Medium InputStream

Answer the first question

For the first question ,“ Why? InputStream Can't read repeatedly ?”, The most direct and rude answer :InputStream It's designed to be unreadable .

We can have a look InputStream in read() Method comments :

 /**
* Reads the next byte of data from the input stream. The value byte is
* returned as an <code>int</code> in the range <code>0</code> to
* <code>255</code>. If no byte is available because the end of the stream
* has been reached, the value <code>-1</code> is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* <p> A subclass must provide an implementation of this method.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
*/
public abstract int read() throws IOException;

Translate it , Its main idea is :

  • Read the next byte of data from the input stream . The byte value returned is from 0 To 255 Between int Type data . If no bytes are available because the stream reaches the end , Then return to -1. Unless there's input data available 、 Or the end of the stream has been detected 、 Or throw an exception , Otherwise, it will be blocked all the time .

According to the note above , We can easily conclude that : Data in the stream , It's not always stored , It will follow the behavior of reading , Be consumed .

Maybe the above explanation is abstract , So we can simply put InputStream Imagine a pipe filled with water , With the flow of water , The water in the pipe will run out sooner or later .

Think about it ,InputStream To and NIO Medium Buffer It's kind of like , But neither InputStream still OutputStream It's all one-way , Or you can only go in 、 Or it can only come out of , and NIO Medium Buffer It's two-way .

Answer the second question

Now that we know InputStream The reason why it can't be read repeatedly , So for the second question ,“ How to read repeatedly HttpServletRequest Medium InputStream?”, The solution is simple . We can get HttpServletRequest Medium InputStream When , Make a backup at the same time .

for example , First the HttpServletRequest Medium InputStream out , To String object , Then take it. String Object to byte[] Save the array back , That's the guarantee HttpServletRequest in InputStream The value of does not change , But we get reusable String object .

Here is an example of the code available , Can guarantee our safe access to HttpServletRequest Medium InputStream object :

public class SafeHttpServletRequestWrapper extends HttpServletRequestWrapper {

private static final String CHARSET_UTF8 = "UTF-8";
private final byte[] body;
private String bodyString;
public SafeHttpServletRequestWrapper(HttpServletRequest request) throws IOException {

super(request);
this.bodyString = StreamUtils.copyToString(request.getInputStream(), Charset.forName(CHARSET_UTF8));
body = bodyString.getBytes(CHARSET_UTF8);
}
public String getBodyString() {

return this.bodyString;
}
@Override
public BufferedReader getReader() throws IOException {

return new BufferedReader(new InputStreamReader(getInputStream()));
}
@Override
public ServletInputStream getInputStream() throws IOException {

final ByteArrayInputStream innerBAIS = new ByteArrayInputStream(body);
return 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 innerBAIS.read();
}
};
}
}

As shown in the above code ,SafeHttpServletRequestWrapper It's a safe HttpServletRequest Packaging . Use mode: :

@Slf4j
public abstract class AbstractFilter implements Filter {

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

try {

SafeHttpServletRequestWrapper requestWrapper = new SafeHttpServletRequestWrapper((HttpServletRequest) servletRequest);
log.info("AbstractFilter servletRequest body is {}", requestWrapper.getBodyString());
filterChain.doFilter(requestWrapper, servletResponse);
} catch (IOException e) {

e.printStackTrace();
}
}
}

As shown in the above code , We will first servletRequest It turned into HttpServletRequest, And then it was packaged as SafeHttpServletRequestWrapper object . stay SafeHttpServletRequestWrapper In the object , It contains our backup InputStream object ( actually , It's packaged as ByteArrayInputStream object ) And the available bodyString character string .

ad locum , If we want to get the original HttpServletRequest in InputStream Object content , We call directly getBodyString() that will do ; If we want to HttpServletRequest Pass it on , We deliver the packaged SafeHttpServletRequestWrapper that will do , Because it already contains the original HttpServletRequest All the information in , And back up InputStream Object content .


reference

版权声明
本文为[CG Guobin]所创,转载请带上原文链接,感谢

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