ServletInputStream多读场景及解决方案

应用场景

如果你打算通过 javax.servlet.Filter 来拦截 POST 请求，并想通过 ServletInputStream 获取 body 的内容，等请求到达实际API时会报错：stream closed :::info 那是因为在Java中的 Stream 流只能使用一次，再次使用时该流已经被关闭了。 :::

解决方案1-Spring自带Wrapper

直接使用 org.springframework.web.util 包下的 ContentCachingRequestWrapper 类即可。

BodyReadFilter

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Component;
import org.apache.commons.io.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.util.ContentCachingRequestWrapper;
@Component
public class BodyReadFilter implements Filter {
    private static final Logger LOGGER = LoggerFactory.getLogger(BodyReadFilter.class);
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
            throws IOException, ServletException {
        ContentCachingRequestWrapper wrappedRequest = new ContentCachingRequestWrapper((HttpServletRequest) servletRequest);
        LOGGER.info("The body of the request was {}", IOUtils.toString(wrappedRequest.getInputStream()));
        filterChain.doFilter(wrappedRequest, servletResponse);
    }
}

解决方案2-自己实现

MultiReadHttpServletRequest

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import org.apache.commons.io.IOUtils;
/*
via https://stackoverflow.com/a/36619972/2257038 and https://stackoverflow.com/a/30748533/2257038
*/
public class MultiReadHttpServletRequest extends HttpServletRequestWrapper {
    private ByteArrayOutputStream cachedBytes;
    public MultiReadHttpServletRequest(HttpServletRequest request) {
        super(request);
    }
    @Override
    public ServletInputStream getInputStream() throws IOException {
        if (cachedBytes == null) cacheInputStream();
        return new CachedServletInputStream(cachedBytes.toByteArray());
    }
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }
    private void cacheInputStream() throws IOException {
        /* Cache the inputstream in order to read it multiple times. For
         * convenience, I use apache.commons IOUtils
         */
        cachedBytes = new ByteArrayOutputStream();
        IOUtils.copy(super.getInputStream(), cachedBytes);
    }
    /* An inputstream which reads the cached request body */
    public static class CachedServletInputStream extends ServletInputStream {
        private final ByteArrayInputStream buffer;
        public CachedServletInputStream(byte[] contents) {
            this.buffer = new ByteArrayInputStream(contents);
        }
        @Override
        public int read() {
            return buffer.read();
        }
        @Override
        public boolean isFinished() {
            return buffer.available() == 0;
        }
        @Override
        public boolean isReady() {
            return true;
        }
        @Override
        public void setReadListener(ReadListener listener) {
            throw new RuntimeException("Not implemented");
        }
    }
}

BodyReadFilter

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Component;
import org.apache.commons.io.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@Component
public class BodyReadFilter implements Filter {
    private static final Logger LOGGER = LoggerFactory.getLogger(BodyReadFilter.class);
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
            throws IOException, ServletException {
        MultiReadHttpServletRequest wrappedRequest = new MultiReadHttpServletRequest((HttpServletRequest) servletRequest);
        LOGGER.info("The body of the request was {}", IOUtils.toString(wrappedRequest.getInputStream()));
        filterChain.doFilter(wrappedRequest, servletResponse);
    }
}

参考文章：Reading a Servlet/Spring Request Body Multiple Times
其他相关文章：https://juejin.im/post/6858037733776949262