java - 当我在 DBPedia 上运行查询时 CATCH block 中的条件

Question

我有一个问题:

我编写了一段 Java 代码，用于在 DBPedia 上执行一些查询。通常，DBPedia 不可用，我会收到此错误:

SEVERE [http-apr-8080-exec-12] com.sun.xml.ws.server.sei.EndpointMethodHandler.invoke Error making the query, see cause for details
 HttpException: 502
    at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execGet(HttpQuery.java:340)
    at com.hp.hpl.jena.sparql.engine.http.HttpQuery.exec(HttpQuery.java:276)
    at com.hp.hpl.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:345)
    at WS.TEST.testmethod(TEST.java:184)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.sun.xml.ws.api.server.InstanceResolver$1.invoke(InstanceResolver.java:246)
    at com.sun.xml.ws.server.InvokerTube$2.invoke(InvokerTube.java:146)
    at com.sun.xml.ws.server.sei.EndpointMethodHandler.invoke(EndpointMethodHandler.java:257)
    at com.sun.xml.ws.server.sei.SEIInvokerTube.processRequest(SEIInvokerTube.java:95)
    at com.sun.xml.ws.api.pipe.Fiber.__doRun(Fiber.java:629)
    at com.sun.xml.ws.api.pipe.Fiber._doRun(Fiber.java:588)
    at com.sun.xml.ws.api.pipe.Fiber.doRun(Fiber.java:573)
    at com.sun.xml.ws.api.pipe.Fiber.runSync(Fiber.java:470)
    at com.sun.xml.ws.server.WSEndpointImpl$2.process(WSEndpointImpl.java:295)
    at com.sun.xml.ws.transport.http.HttpAdapter$HttpToolkit.handle(HttpAdapter.java:515)
    at com.sun.xml.ws.transport.http.HttpAdapter.handle(HttpAdapter.java:285)
    at com.sun.xml.ws.transport.http.servlet.ServletAdapter.handle(ServletAdapter.java:143)
    at com.sun.xml.ws.transport.http.servlet.WSServletDelegate.doGet(WSServletDelegate.java:155)
    at com.sun.xml.ws.transport.http.servlet.WSServletDelegate.doPost(WSServletDelegate.java:189)
    at com.sun.xml.ws.transport.http.servlet.WSServlet.doPost(WSServlet.java:76)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:644)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:534)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
    at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:277)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2381)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2370)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:744)

现在，我想在调用此操作时在我的代码中添加一个 TRY/CATCH block :

QueryExecution qe = query(string);

对于这个错误，我必须在 catch 中插入什么条件？

Answer 1

从您的代码看来它抛出了 HttpException。

这样写:

try
{
QueryExecution qe = query(string);
}
catch (HttpException ex)
{
System.out.println (ex.getMessage());   //Optional
ex.printStackTrace();    //Optional
}

另一个捕获可以是 catch (Exception ex) {..}//它将捕获任何问题。但是，如果您知道确切的异常，请使用确切的。

在最后我写了常见的错误打印，但你可以根据你的问题填写它。