我有一个使用Spring MVC 3.2.0制作的REST Web服务，它也可以通过Spring MVC调用其他REST Web服务。我有以下例外：
25-11-2014 17:49:42-ERROR-ajp-/172.23.111.22:8109-9-pe.com.dummy.BusinessDummyImpl- I/O error on POST request for "http://172.23.111.23/dummy-2/rest/method1":Unexpected end of file from server; nested exception is java.net.SocketException: Unexpected end of file from server
org.springframework.web.client.ResourceAccessException: I/O error on POST request for "http://172.23.111.23/dummy-2/rest/method1":Unexpected end of file from server; nested exception is java.net.SocketException: Unexpected end of file from server
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:499)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:447)
at org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:295)
Caused by: java.net.SocketException: Unexpected end of file from server
at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:747)
at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:608)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1334)
at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:479)
at org.springframework.http.client.SimpleClientHttpResponse.getRawStatusCode(SimpleClientHttpResponse.java:47)
at org.springframework.http.client.AbstractClientHttpResponse.getStatusCode(AbstractClientHttpResponse.java:32)
at org.springframework.web.client.DefaultResponseErrorHandler.getHttpStatusCode(DefaultResponseErrorHandler.java:55)
at org.springframework.web.client.DefaultResponseErrorHandler.hasError(DefaultResponseErrorHandler.java:49)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:485)
... 42 more
它随机发生，当我检查dummy-2 WS上的登录时，没有任何错误迹象。
导致此错误的原因是什么？