讀取Google AppEngine中的Java資源文件

Question

我有一個Google AppEngine Java項目設置，它調用BigQuery來顯示查詢作業的結果。我使用的示例代碼和說明可以在here找到。應用程序運行並從我的開發機器中檢索查詢，但是當我上傳到AppEngine以在appspot.com上測試時，它顯示爲client_secrets.json文件（由於JavaScript URL授權，dev和appspot.com的不同文件）無法使用下面的代碼片段：

static GoogleClientSecrets getClientCredential() throws IOException { 
if (clientSecrets == null) { 

    clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, 
      new InputStreamReader(new FileInputStream(
       new File("WEB-INF/client_secrets.json")))); 

    Preconditions.checkArgument(!clientSecrets.getDetails().getClientId().startsWith("Enter ") 
     && !clientSecrets.getDetails().getClientSecret().startsWith("Enter "), 
     "Enter Client ID and Secret from https://code.google.com/apis/console/?api=bigquery " 
     + "into bigquery-appengine-sample/src/main/resources/client_secrets.json"); 
} 
return clientSecrets; 

}

這裏是我的AppEngine-web.xml中的資源文件的定義：

<resource-files> 
    <include path="**" /> 
    </resource-files> 

的client_secrets.json檔案的妥善包裝在我的戰爭文件。我得到的錯誤是：

>/
Uncaught exception from servlet 
java.io.FileNotFoundException: /base/data/home/apps/s~tactile-reason-849/1.385872137632330782/WEB-INF/client_secrets.json (No such file or directory) 
    at java.io.FileInputStream.open(Native Method) 
    at java.io.FileInputStream.<init>(FileInputStream.java:171) 
    at com.google.api.client.sample.bigquery.appengine.dashboard.ServiceUtils.getClientCredential(ServiceUtils.java:71) 
    at com.google.api.client.sample.bigquery.appengine.dashboard.ServiceUtils.newFlow(ServiceUtils.java:103) 
    at com.google.api.client.sample.bigquery.appengine.dashboard.MainServlet.initializeFlow(MainServlet.java:125) 
    at com.google.api.client.extensions.servlet.auth.oauth2.AbstractAuthorizationCodeServlet.service(AbstractAuthorizationCodeServlet.java:124) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166) 
    at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388) 
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) 
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182) 
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765) 
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418) 
    at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:257) 
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) 
    at org.mortbay.jetty.Server.handle(Server.java:326) 
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542) 
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923) 
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76) 
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404) 
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146) 
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:482) 
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437) 
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444) 
    at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:230) 
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308) 
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300) 
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441) 
    at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:234) 
    at java.lang.Thread.run(Thread.java:745) 

我可以嘗試使用ServletContext.getResourceAsStream（）來代替，但它連接至BigQuery在示例應用程序的類不是一個Servlet類，所以這將需要一些代碼重組正確實施，Google's instructions似乎表明我的代碼應該工作。任何幫助表示讚賞，謝謝！

Answer 1

資源文件不在文件系統上，所以new File("/WEB-INF/client_secrets.json")普通不起作用。相反，你通常需要加載它作爲一種資源：

InputStream resourceStream = Thread.currentThread().getContextClassLoader() 
    .getResourceAsStream("/WEB-INF/client_secrets.json"); 

出於某種原因，AppEngine上不會讓你使用類加載器加載在WEB-INF資源（可以加載在jar文件的資源與上述技術）。

您可以使用File API訪問App中WEB-INF中的路徑，但路徑需要是相對的。假設文件client_secrets.json是在WEB-INF文件夾，這應該工作：

clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, 
    new InputStreamReader(new FileInputStream(
     new File("WEB-INF/client_secrets.json")))); 

要使用File API來讀取WEB-INF下的資源，你也還需要確保您appengine-web.xml文件包括資源在WEB-INF：

<resource-files> 
    <include path="/**.json" /> 
</resource-files> 

你使用Maven /搖籃見Configuring appengine-web.xml和Why can't I read from this file