2
鑑於API端點JsonMappingException：找到了類型
@ApiMethod(name = "sendChallenge", httpMethod = HttpMethod.POST)
public ExchangeList sendChallenge(ChallengeData request) throws Exception {
return getFromDBThenProcess(request);
}
和前端（安卓）沒有合適的構造函數中調用到端點
ExchangeList transfers = service.sendChallenge(request).execute();
我從logcat的以下堆棧跟蹤。
注：我在我的監視服務器控制檯（本地主機），並沒有電話進來
堆棧跟蹤：
04-08 14:58:53.261: D/dalvikvm(940): GC_CONCURRENT freed 1394K, 15% free 12495K/14599K, paused 15ms+15ms, total 75ms
… //[many of those `freed` lines]
04-08 14:58:54.742: D/dalvikvm(940): GC_CONCURRENT freed 1394K, 15% free 12506K/14599K, paused 15ms+16ms, total 85ms
04-08 14:58:55.562: W/System.err(940): com.google.api.client.googleapis.json.GoogleJsonResponseException: 400 Bad Request
04-08 14:58:55.562: W/System.err(940): {
04-08 14:58:55.562: W/System.err(940): "code": 0,
04-08 14:58:55.562: W/System.err(940): "message": "com.google.appengine.repackaged.org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class com.myapi.games.message.ChallengeData]: can not instantiate from JSON object (need to add/enable type information?)\n at [Source: N/A; line: -1, column: -1]"
04-08 14:58:55.572: W/System.err(940): }
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:111)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:38)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.AbstractGoogleClientRequest$1.interceptResponse(AbstractGoogleClientRequest.java:314)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1060)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:412)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:345)
04-08 14:58:55.572: W/System.err(940): at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:463)
04-08 14:58:55.572: W/System.err(940): at com.myapi.games.utils.sendChallenge.doInBackground(sendChallenge.java:70)
04-08 14:58:55.582: W/System.err(940): at com.myapi.games.utils.sendChallenge.doInBackground(sendChallenge.java:1)
04-08 14:58:55.582: W/System.err(940): at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-08 14:58:55.582: W/System.err(940): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
04-08 14:58:55.582: W/System.err(940): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
04-08 14:58:55.582: W/System.err(940): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
04-08 14:58:55.592: W/System.err(940): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
04-08 14:58:55.592: W/System.err(940): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
04-08 14:58:55.592: W/System.err(940): at java.lang.Thread.run(Thread.java:856)
這是關於連接的Android項目的AppEngine上。編譯沒有錯誤，等等。另外，POJO ChallengeData由其他三個的POJO類似於：
public class ChallengeData{
Credit credit;
Coin coin;
Friend friend;
//getters and setters
}
然後信貸和硬幣只包含簡單的字段（如int和string），但朋友包含一些簡單的字段和進一步POJO。
我真的不認爲JSON的深度（即POJO關係）應該重要。但我包括所有相同的細節。