应用引擎中 urlfetch 超过 1M 的问题

Question

要在应用引擎中 fetch() 超过 1M，我使用范围标头，然后结合这些部分。和我的代码：

int startpos=0;
int endpos;
int seg=1;
int len=1;
while(len>0){
endpos=startpos+seg;
httpConn = (HttpURLConnection) u.openConnection();
httpConn.setRequestMethod("GET");
con.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.8.1.14) Gecko/20080404 Firefox/2.0.0.14");

con.setRequestProperty("Range", "bytes=" + startpos + "-" + endpos);  
con.connect();
InputStream in=con.getInputStream();

len=con.getContentLength();
byte[] b=new byte[len];
in.read(b, 0, len);

startpos+=len; 

} 但是当它进入“InputStream in=con.getInputStream();”时，它的调试是“URL Fetch Response too large questions” 所以我不知道这些代码有什么问题。 还有其他方法可以 fetch() 超过 1M 吗？

Answer 1

并非所有 HTTP 服务器都支持范围请求，尤其是在涉及提供动态内容的框架时 - 它们会简单地忽略 Range 标头并将整个响应发送给您。

不过，最近发布的 1.4.0 将 URLFetch 响应限制增加到 32MB，因此您不再需要这样做。

Answer 2

我遇到了同样的问题，并编写了一个小类来使用 HTTP 范围参数在 Appengine 上模拟输入流。它允许您以面向行的方式读取大于限制的文件。我将其附在下面，尽管您可能需要根据您的目的对其进行调整：

package com.theodorebook.AEStreamer;

import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.Arrays;
import java.util.logging.Logger;

/**
 * A class to simulate a stream in appengine, which insists on downloading
 * an entire URL before letting you do anything with it.  This enables one
 * to read files larger than the size limits.
 * 
 * @author Theodore Book (theodorebook at gmail dot com)
 *
 */
public class AEStreamer {
    private static final int BITE_SIZE = 0x10000;   //How big a chunk to grab at a time
    private static final byte TERMINATOR = '\n';    //String terminator

    private int mCurrentPosition = 0;   //The current position in the file
    private int mOffset = -1;   //The offset of the current block
    private long mValidBytes = 0;   //The number of valid bytes in the chunk
    private byte[] mChunk = new byte[BITE_SIZE];
    private boolean mComplete = false;
    private String mURL;

    private static final Logger log = Logger.getLogger(AEStreamer.class.getName());

    public AEStreamer(String url) {
        mURL = url;
    }

    /**
     * Returns the next line from the source, or null on empty
     * @return
     */
    public String readLine() {
        String line = "";

        //See if we have something to read
        if (mCurrentPosition >= mOffset + mValidBytes) {
            if (mComplete)
                return null;
            readChunk();
        }
        if (mValidBytes == 0)
            return null;

        //Read until we reach a terminator
        int endPtr = mCurrentPosition - mOffset;
        while (mChunk[endPtr] != TERMINATOR) {
            endPtr++;

            //If we reach the end of the block
            if (endPtr == mValidBytes) {
                line += new String(Arrays.copyOfRange(mChunk, mCurrentPosition - mOffset, endPtr));
                mCurrentPosition += (endPtr - mCurrentPosition + mOffset);
                if (mComplete) {
                    return line;
                } else {
                    readChunk();
                    endPtr = mCurrentPosition - mOffset;
                }
            }
        }
        line += new String(Arrays.copyOfRange(mChunk, mCurrentPosition - mOffset, endPtr));
        mCurrentPosition += (endPtr - mCurrentPosition + mOffset);
        mCurrentPosition++;
        return line;
    }

    /**
     * Reads the next chunk from the server
     */
    private void readChunk() {
        if (mOffset < 0)
            mOffset = 0;
        else
            mOffset += BITE_SIZE;

        try {
            URL url = new URL(mURL);
            URLConnection request = url.openConnection();
            request.setRequestProperty("Range", "bytes=" + (mOffset + 1) + "-" + (mOffset + BITE_SIZE)); 
            InputStream inStream = request.getInputStream();
            mValidBytes = inStream.read(mChunk);
            inStream.close();
        } catch (Exception e) {
            log.severe("Unable to read " + mURL + ": " + e.getLocalizedMessage());
            mComplete = true;
            mValidBytes = 0;
            return;
        }

        if (mValidBytes < BITE_SIZE)
            mComplete = true;

        //log.info("Read " + mValidBytes + " bytes");
    }
}