问题
I have no idea in what extend GAE is not easy to understand :(
My servlet manipulate a json string and then I'm trying to store it in datastore. When I run the application I'm getting this output:
Jan 27, 2014 6:59:04 PM com.google.appengine.api.datastore.dev.LocalDatastoreService load
INFO: The backing store, D:\Android\IntelliJ IDEA\workspace\EyeBall\AppEngine\out\artifacts\AppEngine_war_exploded\WEB-INF\appengine-generated\local_db.bin, does not exist. It will be created.
1
2
3
4
5
7
***
***
***
***
***
8
9
Although it's mentioned that local_db.bin will be created but when I navigate to that directory the file is not there. Also, when I open http://localhost:8080/_ah/admin/datastore in browser nothing displays in Entity Kind drop down list.
So wtf happene to local_db.bin? Why it doesn't generates? any suggestion would be appreciated. thanks.
================== UPDATE: I added my code based on request.
private static final String NO_DEVICE_ID = "FFFF0000";
private static final String SAMPLE_JSON = "{\"history\":[{\"date\":null,\"info\":null,\"title\":\"Maybank2u.com\",\"url\":\"https://www.maybank2u.com.my/mbb/Mobile/info.do\",\"visits\":14},{\"date\":null,\"info\":null,\"title\":\"Maybank2u.com\",\"url\":\"https://www.maybank2u.com.my/mbb/Mobile/adaptInfo.do\",\"visits\":4},{\"date\":null,\"info\":null,\"title\":\"Maybank2u.com\",\"url\":\"http://www.maybank2u.com.my/mbb_info/m2u/public/personalBanking.do\",\"visits\":16},{\"date\":null,\"info\":null,\"title\":\"Maybank2u.com Online Financial Services\",\"url\":\"https://www.maybank2u.com.my/mbb/m2u/common/M2ULogin.do?action=Login\",\"visits\":52},{\"date\":null,\"info\":null,\"title\":\"BBC\",\"url\":\"http://www.bbc.co.uk/persian/\",\"visits\":16}]}";
private static final String QUERY_HISTORY_DEVICE = "SELECT m FROM HistoryDeviceJPA m WHERE m.userUUID = :keyword ORDER BY m.domain ASC";
private static final String QUERY_HISTORY = "SELECT m FROM HistoryJPA m WHERE m.pageAddress = :keyword";
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// displayError(response, "The page doesn't support httpGet");
String deviceId = NO_DEVICE_ID;
String content = SAMPLE_JSON;
System.out.println("1");
HistoryBrowser historyBrowser = parseJson(content);
if(historyBrowser == null)
return;
System.out.println("2");
List<HistoryBrowser.BrowserInfo> historyList = historyBrowser.getHistory();
if(historyList == null)
return;
System.out.println("3");
List<HistoryDeviceJPA> historyDeviceJPAList = new ArrayList<HistoryDeviceJPA>(historyList.size());
for(int i=0; i<historyList.size(); i++) {
try {
HistoryBrowser.BrowserInfo browser = historyList.get(i);
HistoryDeviceJPA historyDeviceJPA = new HistoryDeviceJPA();
historyDeviceJPA.setUserUUID(deviceId);
historyDeviceJPA.setDomain(getDomainName(browser.getUrl()));
historyDeviceJPA.setPageAddress(browser.getUrl());
historyDeviceJPA.setPageTitle(browser.getTitle());
historyDeviceJPA.setPageVisits(browser.getVisits());
historyDeviceJPAList.add(historyDeviceJPA);
} catch (URISyntaxException e) {
System.out.println(e.getMessage());
}
}
System.out.println("4");
// get history of device from data store
EntityManager em = EMF.get().createEntityManager();
Query q = em.createQuery(QUERY_HISTORY_DEVICE).setParameter("keyword", deviceId);
@SuppressWarnings("unchecked")
List<HistoryDeviceJPA> dbList = (List<HistoryDeviceJPA>) q.getResultList();
System.out.println("5");
// If there is no result (shows there is no record for that device)
if(dbList == null)
addHistoryDeviceJPAToDs(historyDeviceJPAList);
else {
System.out.println("7");
// find each item in datastore and replace them if needed
// if current page visit is less ot equal than previous visit don't do anything (remove item form historyDeviceJPAList)
outerLoop:
for(int i=0; i<historyDeviceJPAList.size(); i++) {
HistoryDeviceJPA deviceItem = historyDeviceJPAList.get(i);
System.out.println("***");
for(int j=0; j<dbList.size(); j++) {
HistoryDeviceJPA dbItem = dbList.get(j);
if(deviceItem.getPageAddress().equalsIgnoreCase(dbItem.getPageAddress())) {
if(deviceItem.getPageVisits() > dbItem.getPageVisits()) {
long diff = deviceItem.getPageVisits() - dbItem.getPageVisits();
dbItem.setPageVisits(deviceItem.getPageVisits());
HistoryJPA historyJPA = findHistoryJPA(dbItem.getPageAddress());
historyJPA.setPageVisits(historyJPA.getPageVisits() + diff);
// update datastore
addHistoryDeviceJPAToDs(dbItem);
addHistoryJPAToDs(historyJPA);
// don't check other items of j list
break outerLoop;
}
}
}
}
System.out.println("8");
}
System.out.println("9");
// http://www.sohailaziz.com/2012/06/scheduling-activities-services-and.html
// https://dev.twitter.com/docs/api/1.1
// https://developers.google.com/appengine/docs/java/datastore/jdo/creatinggettinganddeletingdata?csw=1#Updating_an_Object
// http://en.wikibooks.org/wiki/Java_Persistence/Inheritance
}
and 6 is here:
private void addHistoryDeviceJPAToDs(List<HistoryDeviceJPA> list) {
System.out.println("6");
EntityManager em = EMF.get().createEntityManager();
try {
for (int i=0; i<list.size(); i++) {
System.out.println("=> " + i + " - " + list.get(i).toString());
em.getTransaction().begin();
em.persist(list.get(i));
em.getTransaction().commit();
}
} finally {
em.close();
}
}
回答1:
after debug I found the problem is in this line:
List<HistoryDeviceJPA> dbList = (List<HistoryDeviceJPA>) q.getResultList();
if(dbList == null)
addHistoryDeviceJPAToDs(historyDeviceJPAList);
'dbList' is never null and it's size is 0 if there is nothing in datastore. That's why addHistoryDeviceJPAToDs method never invoked. By changing the code to following problem solved and local db created.
List<HistoryDeviceJPA> dbList = (List<HistoryDeviceJPA>) q.getResultList();
if(dbList == null)
return;
System.out.println("5");
// If there is no result (shows there is no record for that device)
if(dbList.size() == 0)
addHistoryDeviceJPAToDs(historyDeviceJPAList);
回答2:
For other people who come across the same issue --
GAE will not create local_db.bin until you put data in the datastore. So if the file is not there, there is likely a bug in the application code.
来源：https://stackoverflow.com/questions/21379265/gae-local-datastore-does-not-create