java - 尝试为实体创建 key 时出现 IllegalArgumentException

Question

我正在使用 Google App Engine，但遇到了困难。我正在尝试为我的实体创建一个 key 。这是代码:

Element child = (Element) itr.next();
                String name = "";
                if(child.getQualifiedName().equals("name")){
                    name += child.getText();
                }
                Key drugKey = KeyFactory.createKey("DrugTarget", name);

我 100% 确定 child.getText() 不会返回 null。我已经测试过了。我有另一段代码可以完美地创建 Key。两者看起来彼此相似。

String drug = req.getParameter("drugname");
Key drugKey = KeyFactory.createKey("DrugTarget", drug);

我真的不明白为什么会报错。第一段代码属于一个 Java 类，我在 Java Servlet 类中调用这个类。第二个属于 Java Servlet 类。但我认为问题是不同的。能否请你帮忙？谢谢。

编辑部分:

if(child.getQualifiedName().equals("name")){
                    if(child.getText() != null){
                    name = child.getText();
                    }
                    else{
                        name = "asd";
                    }
                }

我将它放入我的代码中，仍然出现空错误。 child.getText() 不返回 null 且名称不等于“asd”。

忘记添加错误信息:

Uncaught exception from servlet
java.lang.IllegalArgumentException: name cannot be null or empty
at com.google.appengine.api.datastore.KeyFactory.createKey(KeyFactory.java:73)
at com.google.appengine.api.datastore.KeyFactory.createKey(KeyFactory.java:60)
at guestbook.saxParser2.getDrug(saxParser2.java:42)
at guestbook.SignGuestbookServlet.doPost(SignGuestbookServlet.java:77)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
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$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:102)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$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:266)
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:447)
at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:454)
at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:461)
at com.google.tracing.TraceContext.runInContext(TraceContext.java:703)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:338)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:330)
at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:458)
at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
at java.lang.Thread.run(Thread.java:679)

Answer 1

错误信息说:

Uncaught exception from servlet
java.lang.IllegalArgumentException: name cannot be null or empty

以及您的实际代码:

String name = "";
if(child.getQualifiedName().equals("name")){
  name += child.getText();
}
Key drugKey = KeyFactory.createKey("DrugTarget", name);

所以在 if 语句中 child.getQualifiedName().equals("name")表达式为假，'name' 字符串变量仍然是一个空字符串 ( String name = "" )。 这就是错误消息所说的:在 Key drugKey = KeyFactory.createKey("DrugTarget", name); 处不能为空字符串作为参数。

编辑: 试试这个:

Element child = (Element) itr.next();
String name = "defaultName";
if(child.getQualifiedName().equals("name")){
  name = child.getText();
}
Key drugKey = KeyFactory.createKey("DrugTarget", name);

问题不在于 child.getText()是否返回 null，问题是您的 if 语句中的表达式将是 false , 所以 name += child.getText();无法访问并且 name仍然是一个空字符串。

if(child.getQualifiedName().equals("name")){
      name += child.getText();
}