GAE，本地数据存储不创建 [英] GAE, Local datastore does not create
本文介绍了GAE，本地数据存储不创建的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我不知道GAE在什么情况下不易理解：（$ / b>
我的servlet处理一个json字符串，然后我试图将它存储在数据存储区。
当我运行应用程序时，我得到了这个输出：
2014年1月27日6:59:04 PM com.google.appengine.api.datastore.dev.LocalDatastoreService加载
INFO：后备存储区D：\Android\IntelliJ IDEA\workspace\EyeBall\AppEngine\out\artifacts\\ \\ AppEngine_war_exploded \WEB-INF \appengine-generated\local_db.bin不存在，它将被创建。
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***
***
***
***
***
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尽管提到将创建local_db.bin，但是当我导航到该目录时，文件当我在浏览器中打开 http：// localhost：8080 / _ah / admin / datastore 时，在Entity Kind下拉列表中不显示任何内容。
因此，wtf发生在local_db.bin？为什么它不会生成？
任何建议，将不胜感激。感谢。
==================
更新：
我根据请求添加了我的代码。
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\ ：空，\ info\ ：空，\ title\ ：\ Maybank2u.com\ \ url\ ：\ https://www.maybank2u.com.my/mbb/Mobile/adaptInfo.do\，\ visits\：4}，{\ date\：空， \ info\：空，\ 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？行动= Login\，\ visits\：52}，{\ date\：空，\ info\：NU LL，\ 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请求，HttpServletResponse响应）抛出ServletException，IOException {
// displayError（response，The page does not support httpGet）;
字符串deviceId = NO_DEVICE_ID;
字符串内容= SAMPLE_JSON;
System.out.println（1）;
HistoryBrowser historyBrowser = parseJson（content）;
if（historyBrowser == null）
return;
System.out.println（2）;
列表< HistoryBrowser.BrowserInfo> historyList = historyBrowser.getHistory（）;
if（historyList == null）
return;
System.out.println（3）;
列表< 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）;
//从数据存储获取设备的历史记录
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）;
//如果没有结果（显示该设备没有记录）
if（dbList == null）
addHistoryDeviceJPAToDs（historyDeviceJPAList）;
else {
System.out.println（7）;
//找到数据存储中的每个项目，并根据需要替换它们
//如果当前页面访问不如前一次访问等于不执行任何操作（删除项目形式historyDeviceJPAList）
outerLoop：
for（int i = 0; i< historyDeviceJPAList.size（）; i ++）{
HistoryDeviceJPA deviceItem = historyDeviceJPAList.get（i）;
System.out.println（***）;
for（int j = 0; j
$ b $ if（deviceItem.getPageVisits（）> dbItem.getPageVisits（））{
（deviceItem.getPageAddress（）。equalsIgnoreCase（dbItem.getPageAddress（）））{
if long diff = deviceItem.getPageVisits（） - dbItem.getPageVisits（）;
dbItem.setPageVisits（deviceItem.getPageVisits（））;
HistoryJPA historyJPA = findHistoryJPA（dbItem.getPageAddress（））;
historyJPA.setPageVisits（historyJPA.getPageVisits（）+ diff）;
//更新数据存储
addHistoryDeviceJPAToDs（dbItem）;
addHistoryJPAToDs（historyJPA）;
//不检查j列表中的其他项目
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
}
和6在这里：
private void addHistoryDeviceJPAToDs（List< HistoryDeviceJPA> list）{
System.out.println（6）;
EntityManager em = EMF.get（）。createEntityManager（）;
尝试{
for（int i = 0; i< list.size（）; i ++）{
System.out.println（=>+ i + - + list.get（ⅰ）的ToString（））;
em.getTransaction（）。begin（）;
em.persist（list.get（i））;
em.getTransaction（）。commit（）;
}
} finally {
em.close（）;
}
}
解决方案
调试后我发现问题在这一行：
List< HistoryDeviceJPA> dbList =（List< HistoryDeviceJPA>）q.getResultList（）;
if（dbList == null）
addHistoryDeviceJPAToDs（historyDeviceJPAList）;
'dbList'永远不会为空，如果数据存储区中没有任何内容，则其大小为0。这就是为什么从未调用 addHistoryDeviceJPAToDs 方法的原因。
列表< HistoryDeviceJPA>通过更改代码来解决以下问题并创建本地数据库。 dbList =（List< HistoryDeviceJPA>）q.getResultList（）;
if（dbList == null）
return;
System.out.println（5）;
//如果没有结果（显示该设备没有记录）
if（dbList.size（）== 0）
addHistoryDeviceJPAToDs（historyDeviceJPAList）;
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.
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***
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***
***
***
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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();
}
}
解决方案
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);
这篇关于GAE，本地数据存储不创建的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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