ServletInputStream的重复读取（多次读取）

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在使用Servlet进行Web开发的时候，有时候为了增加必要的业务处理而又不想修改现有的程序，往往采用Filter。这样在各个Filter中可能都要读取ServletInputStream流的内容，而ServletInputStream却只能读一次，这时候必须备份HttpServleRequest。

class BufferedServletInputStream extends ServletInputStream {
private ByteArrayInputStream inputStream;
public BufferedServletInputStream(byte[] buffer) {
this.inputStream = new ByteArrayInputStream( buffer );
}
@Override
public int available() throws IOException {
return inputStream.available();
}
@Override
public int read() throws IOException {
return inputStream.read();
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
return inputStream.read( b, off, len );
}
}

class BufferedServletRequestWrapper extends HttpServletRequestWrapper {
private byte[] buffer;
public BufferedServletRequestWrapper(HttpServletRequest request) throws IOException {
super( request );
InputStream is = request.getInputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte buff[] = new byte[ 1024 ];
int read;
while( ( read = is.read( buff ) ) > 0 ) {
baos.write( buff, 0, read );
}
this.buffer = baos.toByteArray();
}
@Override
public ServletInputStream getInputStream() throws IOException {
return new BufferedServletInputStream( this.buffer );
}
}

在Filter的doFilter（）或者Servlet的doPost（）中，

//备份HttpServletRequest
HttpServletRequest httpRequest = (HttpServletRequest)request;
httpRequest = new BufferedServletRequestWrapper( httpRequest );
//使用流
InputStream is = request.getInputStream();
//其他业务逻辑
//将request 传到下一个Filter
chain.doFilter(request, response);