爲什麼我會收到com.vaadin.event.ListenerMethod $ MethodException？

我的小型數據庫（DERBY）應用程序遇到很大問題。我得到這樣一個錯誤，當我按一下按鈕：

2011-12-25 04:21:38 com.vaadin.Application terminalError 
SEVERE: Terminal error: 
com.vaadin.event.ListenerMethod$MethodException 
Cause: java.lang.NullPointerException 
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:532) 
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:164) 
    at com.vaadin.ui.AbstractComponent.fireEvent(AbstractComponent.java:1219) 
    at com.vaadin.ui.Button.fireClick(Button.java:550) 
    at com.vaadin.ui.Button.changeVariables(Button.java:217) 
    at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.changeVariables(AbstractCommunicationManager.java:1445) 
    at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.handleVariableBurst(AbstractCommunicationManager.java:1393) 
    at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.handleVariables(AbstractCommunicationManager.java:1312) 
    at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.doHandleUidlRequest(AbstractCommunicationManager.java:763) 
    at com.vaadin.terminal.gwt.server.CommunicationManager.handleUidlRequest(CommunicationManager.java:296) 
    at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:501) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164) 
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100) 
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395) 
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250) 
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188) 
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) 
    at java.lang.Thread.run(Unknown Source) 
Caused by: java.lang.NullPointerException 
    at com.example.expert_system.Knowledge.insertPhone(Knowledge.java:280) 
    at com.example.expert_system.Knowledge.buttonClick(Knowledge.java:262) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:512) 
    ... 27 more

我得到這個只有當我試圖調用從類DATABASE_ENGINE方法。

Database_engine.java：

private static String dbURL = "jdbc:derby://localhost:1527/Knowledge;create=true;user=erni;password=2ngxc3"; 
private static String tableName = "ERNI.PHONE"; 
private static Connection conn = null; 
private static Statement stmt = null; 




private void createConnection() 
{ 
    try 
    { 
     Class.forName("org.apache.derby.jdbc.ClientDriver").newInstance(); 
     //Get a connection 
     conn = DriverManager.getConnection(dbURL); 
    } 
    catch (Exception except) 
    { 
     except.printStackTrace(); 
    } 
} 


public void insertPhone(String producer, String model, String construction, String display_size, String system) 
{ 

    createConnection(); 
    try 
    { 
     stmt = conn.createStatement(); 
     stmt.execute("insert into " + tableName + "(\"producer\",\"model\", \"construction\",\"dispaly_size\",\"system\") values (" + producer + "','" + model + "','" + construction + "','" + display_size + "','" + system +"')"); 
     stmt.close(); 
     //INSERT INTO ERNI.PHONE ("producer", "model", "construction", "display_size", "system") VALUES ('placek', 'na', 'oleju', 'mama ', 'krzyczy'); 

    } 
    catch (SQLException sqlExcept) 
    { 
     sqlExcept.printStackTrace(); 
     //System.err.println("Exception: "+sqlExcept.getMessage()); 
    } finally { 
     closeConnection(); 
    } 

} 



private void closeConnection() 
{ 
    try 
    { 
     if (stmt != null) 
     { 
      stmt.close(); 
     } 
     if (conn != null) 
     { 
      DriverManager.getConnection(dbURL + ";shutdown=true"); 
      conn.close(); 
     }   
    } 
    catch (SQLException sqlExcept) 
    { 

    } 

}

和形式方法的代碼：

public void buttonClick(ClickEvent event) { 
     Button source = event.getButton(); 
     // 
     if (source == button_2) { 


      insertPhone(); 
      getWindow().showNotification("Open " + producerBox.getValue().toString() +" "+ 
        model.getValue().toString()+" "+ 
        constructionBox.getValue().toString()+" "+ 
        displayBox.getValue().toString()+" "+ 
        systemBox.getValue().toString()); 

      setReadOnly(true); 
      getWindow().showNotification(systemBox.getInputPrompt()); 
     } else if (source == button_1) { 
      discard(); 
      setReadOnly(true); 
      getWindow().showNotification("clear executed"); 
     } 
    } 

    private void insertPhone() { 
     Database_engine addPhone = new Database_engine(); 
     addPhone.insertPhone(producerBox.getValue().toString(), 
          model.getValue().toString(), 
          constructionBox.getValue().toString(), 
          displayBox.getValue().toString(), 
          systemBox.getValue().toString()); 

    } 
    private void discard() { 
     producerBox.setValue(null); 
     model.setValue(""); 
     constructionBox.setValue(null); 
     displayBox.setValue(null); 
     systemBox.setValue(null); 
     otherColSelect.setValue(null); 
     comColSelect.setValue(null); 

    }

請告訴我，我做錯了。

好的我檢查了所有建議。當我調試我得到了這樣的答案代碼「源未找到」

我寫了一個主要的方法來測試類和我得到：

org.apache.derby.client.am.SqlException: Syntax error: Encountered "\',\'" at line 1, column 83. 
    at org.apache.derby.client.am.Statement.completeSqlca(Unknown Source) 
    at org.apache.derby.client.am.Statement.completeExecuteImmediate(Unknown Source) 
    at org.apache.derby.client.net.NetStatementReply.parseEXCSQLIMMreply(Unknown Source) 
    at org.apache.derby.client.net.NetStatementReply.readExecuteImmediate(Unknown Source) 
    at org.apache.derby.client.net.StatementReply.readExecuteImmediate(Unknown Source) 
    at org.apache.derby.client.net.NetStatement.readExecuteImmediate_(Unknown Source) 
    at org.apache.derby.client.am.Statement.readExecuteImmediate(Unknown Source) 
    at org.apache.derby.client.am.Statement.flowExecute(Unknown Source) 
    at org.apache.derby.client.am.Statement.executeX(Unknown Source) 
    at org.apache.derby.client.am.Statement.execute(Unknown Source) 
    at com.example.expert_system.Database_engine.insertPhone(Database_engine.java:56) 
    at com.example.expert_system.Database_engine.main(Database_engine.java:24)

線56 stmt.execute("insert into " + tableName + " (producer, model, construction, display_size, system) values (" + db_producer + "','" + db_model + "','" + db_construction + "','" + db_display_size + "','" + db_system +"')");

但有一切都OK。我想是這樣？

有什麼建議？

來源

2011-12-25 erni

哪個版本的Vaadin是。您使用的是？Knowledge.java中的哪一行是280？ – miq 2011-12-25 15:25:19

我正在使用Vaadin Plug-in for Eclipse並且版本爲2.0.1。行280在insertClick方法中調用了buttonClick方法 – erni 2011-12-25 20:34:41

您是否嘗試過調試該代碼並查看哪個對象爲空？我很確定調試將顯示導致NullPointerException的對象。 – miq 2011-12-26 08:39:13

正如它說你的SQL有語法錯誤。在SQL您有：

...值（「+ db_producer +」 ''」 ......

其中包含不匹配的單引號

來源

2011-12-27 09:28:55 eeq

好的我改變了這一點。它適用於我使用此代碼

public static void main(String args[]) { \t // \t createConnection(); \t // \t insertPhone("p1", "p2", "p3", "p4", "p5"); // \t selectPhone(); // \t closeConnection(); \t \t // }

從此類中調用它時，但是當我嘗試從 – erni 2011-12-27 13:06:11

調用此方法時，現在一切都清楚了，我得到例外的原因是服務器中缺少文件derbyclien.jar/lib目錄下。感謝幫助！！！ – erni 2011-12-27 20:52:32

您的createConnection方法可能不成功，或者您的createStatement調用不成功，將「conn」留空。

來源

2011-12-26 01:38:11

I特別是，在運行程序之前，確保Derby Network Server在端口1527上啓動。 – 2011-12-26 15:37:34

服務器已啓動並在端口號1527上運行。 – erni 2011-12-26 22:56:05

爲什麼我會收到com.vaadin.event.ListenerMethod $ MethodException？

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