Server redirected too many times (20) 是什么错误？

我在读取远程网页源码时，发现了这样的错误，这是怎么回事呢？
Server redirected too many  times (20)java.net.ProtocolException: Server redirected too many  times (20)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1141)
at java.net.URL.openStream(URL.java:1007)
at mypack.GatherNewUrlsBean.getSourceContent(GatherNewUrlsBean.java:176)
at mypack.GatherNewUrlsBean.getArea(GatherNewUrlsBean.java:210)
at mypack.GatherNewUrlsBean.gatherNewURLs(GatherNewUrlsBean.java:137)
at mypack.GatherNewUrlsBean.setNewURLs(GatherNewUrlsBean.java:43)
at mypack.GatherNewUrls.doGet(GatherNewUrls.java:59)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:834)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:640)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1286)
at java.lang.Thread.run(Thread.java:595)