ServletInputStream的重復讀取（多次讀取）（轉）

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在使用Servlet進行Web開發的時候，有時候為了增加必要的業務處理而又不想修改現有的程序，往往采用Filter。這樣在各個Filter中可能都要讀取ServletInputStream流的內容，而ServletInputStream卻只能讀一次，這時候必須備份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，

//備份HttpServletRequest
HttpServletRequest httpRequest = (HttpServletRequest)request;
httpRequest = new BufferedServletRequestWrapper( httpRequest );
//使用流
InputStream is = request.getInputStream();
//其他業務邏輯
//將request 傳到下一個Filter
chain.doFilter(request, response);