使用NullPointerException发布http请求时，我得到DefaultHttpClient，如下所示：
java.lang.NullPointerException
at org.apache.http.impl.conn.AbstractPoolEntry.layerProtocol(AbstractPoolEntry.java:305)
at org.apache.http.impl.conn.AbstractPooledConnAdapter.layerProtocol(AbstractPooledConnAdapter.java:146)
at org.apache.http.impl.client.DefaultRequestDirector.establishRoute(DefaultRequestDirector.java:670)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:375)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:653)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:627)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:616)
我检查了AbstractPoolEntry的源代码：
272 public void layerProtocol(HttpContext context, HttpParams params)
273 throws IOException {
274
275 //@@@ is context allowed to be null? depends on operator?
276 if (params == null) {
277 throw new IllegalArgumentException
278 ("Parameters must not be null.");
279 }
280
281 if ((this.tracker == null) || !this.tracker.isConnected()) {
282 throw new IllegalStateException("Connection not open.");
283 }
284 if (!this.tracker.isTunnelled()) {
285 //@@@ allow this?
286 throw new IllegalStateException
287 ("Protocol layering without a tunnel not supported.");
288 }
289 if (this.tracker.isLayered()) {
290 throw new IllegalStateException
291 ("Multiple protocol layering not supported.");
292 }
293
294 // - collect the arguments
295 // - call the operator
296 // - update the tracking data
297 // In this order, we can be sure that only a successful
298 // layering on top of the connection will be tracked.
299
300 final HttpHost target = tracker.getTargetHost();
301
302 connOperator.updateSecureConnection(this.connection, target,
303 context, params);
304
305 this.tracker.layerProtocol(this.connection.isSecure());
306
307 } // layerProtocol
似乎它不会在第305行抛出任何异常。
有人能给我一些建议吗？
PS：我将ThreadSafeClientConnManager设置为DefaultHttpClient