如何构建可重复读取inputStream的request

目录

• 构建可重复读取inputStream的request
• request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<String> 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();
			}

		};

	}
	@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);
	}
}

调用

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);

		//数据读取处理
		//...
		//将requestWrapper专递给后面的过滤器
		filterChain.doFilter(requestWrapper, httpResponse);
	}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。