运行nutch报错：unzipBestEffort returned null
报错信息：fetch of http://szs.mof.gov.cn/zhengwuxinxi/zhengcefabu/201402/t20140224_1046354.html failed with: java.io.IOException: unzipBestEffort returned null
完整的报错信息为：
2014-03-12 16:48:38,031 ERROR http.Http - Failed to get protocol output java.io.IOException: unzipBestEffort returned null at org.apache.nutch.protocol.http.api.HttpBase.processGzipEncoded(HttpBase.java:317) at org.apache.nutch.protocol.http.HttpResponse.<init>(HttpResponse.java:164) at org.apache.nutch.protocol.http.Http.getResponse(Http.java:64) at org.apache.nutch.protocol.http.api.HttpBase.getProtocolOutput(HttpBase.java:140) at org.apache.nutch.fetcher.Fetcher$FetcherThread.run(Fetcher.java:703) 2014-03-12 16:48:38,031 INFO fetcher.Fetcher - fetch of http://szs.mof.gov.cn/zhengwuxinxi/zhengcefabu/201402/t20140224_1046354.html failed with: java.io.IOException: unzipBestEffort returned null 2014-03-12 16:48:38,031 INFO fetcher.Fetcher - -finishing thread FetcherThread, activeThreads=0
由此可知抛出异常的代码位于src/plugin/lib-http/src/java/org/apache/nutch/protocol/http/api/HttpBase.java（lib-http插件）类的processGzipEncoded方法的317行：
byte[] content;
if (getMaxContent() >= 0) {
content = GZIPUtils.unzipBestEffort(compressed, getMaxContent());
} else {
content = GZIPUtils.unzipBestEffort(compressed);
}
if (content == null)
throw new IOException("unzipBestEffort returned null");nutch1.7\src\plugin\protocol-http\src\java\org\apache\nutch\protocol\http\HttpResponse.java（protocol-http插件）的164行调用了processGzipEncoded方法：
readPlainContent(in);
String contentEncoding = getHeader(Response.CONTENT_ENCODING);
if ("gzip".equals(contentEncoding) || "x-gzip".equals(contentEncoding)) {
content = http.processGzipEncoded(content, url);
} else if ("deflate".equals(contentEncoding)) {
content = http.processDeflateEncoded(content, url);
} else {
if (Http.LOG.isTraceEnabled()) {
Http.LOG.trace("fetched " + content.length + " bytes from " + url);
}
}通过Firefox的Firebug工具可查看该URL的响应头为Content-Encoding：gzip，Transfer-Encoding：chunked。
解决方法如下：
1、修改文件nutch1.7\src\java\org\apache\nutch\metadata\HttpHeaders.java，增加一个field：
public final static String TRANSFER_ENCODING = "Transfer-Encoding";
2、修改文件nutch1.7\src\plugin\protocol-http\src\java\org\apache\nutch\protocol\http\HttpResponse.java，替换第160行代码readPlainContent(in);为如下代码
String transferEncoding = getHeader(Response.TRANSFER_ENCODING);
if(transferEncoding != null && "chunked".equalsIgnoreCase(transferEncoding.trim())){
readChunkedContent(in, line);
}else{
readPlainContent(in);
}3、http内容长度限制不能使用负值，只能使用一个大整数：
<property> <name>http.content.limit</name> <value>655360000</value> </property>
4、因为修改了核心代码和插件代码，所以需要重新编译打包发布，执行nutch1.7\build.xml的默认target：runtime
cd nutch1.7 ant
提交BUG：