如何構建可重複讀取inputStream的request

2022-03-15 13:02:39

構建可重複讀取inputStream的request

我們知道，request的inputStream只能被讀取一次，多次讀取將報錯，那麼如何才能重複讀取呢？答案之一是：增加緩衝，記錄已讀取的內容。

程式碼如下所示：

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: 可重複讀取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);
    }
}

接下來，需要一個對應的Filter.

程式碼如下所示：

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
    }
}

最後，需要在web.xml中，增加該Filter的設定（略）。

request中inputStream多次讀取

在使用HTTP協定實現應用間介面通訊時，伺服器端讀取使用者端請求過來的資料，會用到request.getInputStream()，第一次讀取的時候可以讀取到資料，但是接下來的讀取操作都讀取不到資料。

原因

一個InputStream物件在被讀取完成後，將無法被再次讀取，始終返回-1；

InputStream並沒有實現reset方法（可以重置首次讀取的位置），無法實現重置操作；

解決方法（快取讀取到的資料）

使用request、session等來快取讀取到的資料,這種方式很容易實現，只要setAttribute和getAttribute就行；

使用HttpServletRequestWrapper來包裝HttpServletRequest，在中初始化讀取request的InputStream資料，以byte[]形式快取在其中，然後在Filter中將request轉換為包裝過的request；

程式碼

編寫rHttpServletRequestWrapper子類，用來處理請求資料

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<String> e = request.getHeaderNames();
		while (e.hasMoreElements())
		{
			String name = (String) e.nextElement();
			String value = request.getHeader(name);
			log.debug("HttpServletRequest頭資訊：{}-{}", 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();
			}
			
		};
		
	}
	@Override
	public String getHeader(String name)
	{
		return super.getHeader(name);
	}
	@Override
	public Enumeration<String> getHeaderNames()
	{
		return super.getHeaderNames();
	}
	@Override
	public Enumeration<String> getHeaders(String name)
	{
		return super.getHeaders(name);
	}
}

呼叫

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);
		
		//資料讀取處理
		//...
		//將requestWrapper專遞給後面的過濾器
		filterChain.doFilter(requestWrapper, httpResponse);
	}

以上為個人經驗，希望能給大家一個參考，也希望大家多多支援it145.com。

如何構建可重複讀取inputStream的request

目錄

構建可重複讀取inputStream的request

request中inputStream多次讀取

原因

解決方法（快取讀取到的資料）

程式碼

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