Tomcat：空指針嘗試訪問Web服務時出現異常

Question

我有一個包含Web服務的動態Web項目。我已經將它作爲WAR文件導出，並將其放在tomcat的webapps目錄中。 Tomcat顯示該Web應用程序正在運行。當我嘗試調用我的服務中的一項操作時，出現以下異常：

java.lang.NullPointerException 
    sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294) 
    java.lang.ClassLoader.loadClass(ClassLoader.java:247) 
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1629) 
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559) 
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:461) 
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) 
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931) 
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) 
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004) 
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) 
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) 
    java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) 
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) 
    java.lang.Thread.run(Thread.java:680) 

任何想法這意味着什麼？

這裏是我的班級定義的網絡服務：

package webservice;

import java.sql.*; 

import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.PathParam; 
import javax.ws.rs.Produces; 
import javax.ws.rs.QueryParam; 
import javax.ws.rs.HeaderParam; 
import javax.ws.rs.core.MediaType; 

@Path("/operations") 
public class NotifyWebService { 

    @Path("/insertNewPatron") 
    @GET 

    public String insertNewPatron(@QueryParam("cardNumber")String cardNumber, 
            @QueryParam("pin") String pin, 
            @QueryParam("nickname") String nickname, 
            @QueryParam("deviceID")String deviceID) throws Exception { 


     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxxxx;"; 




      Connection c = DriverManager.getConnection(connectionUrl); 

      String insertPatronStatement = "INSERT INTO dbo.Patron VALUES ('"+cardNumber+"','"+pin+"','"+nickname+"')"; 
      String insertDeviceOwner = "INSERT INTO dbo.DeviceOwner VALUES ('"+deviceID+"','"+cardNumber+"')"; 
      Statement state = null; 

      state = c.createStatement(); 
      state.executeUpdate(insertPatronStatement); 
      state.executeUpdate(insertDeviceOwner); 


      c.close(); 


      return "true"; 
    } 


    @Path("/initializeDevice") 
    @GET 

    public String initializeDevice(@QueryParam("deviceID")String deviceID) throws Exception{ 

     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String insertDeviceStatement = "INSERT INTO dbo.Devices VALUES ('"+deviceID+"',1,3,1,3)"; 
     Statement state = c.createStatement(); 
     state.executeUpdate(insertDeviceStatement); 


     return "true"; 
    } 


    @Path("/updateDevicePreferences") 
    @GET 

    public String updateDevicePreferences(@QueryParam("deviceID") String deviceID, 
              @QueryParam("dueDateNotice")String dueDateNotice, 
              @QueryParam("dueDateNoticeAdvance") String dueDateNoticeAdvance, 
              @QueryParam("holdsNotice") String holdsNotice, 
              @QueryParam("eventNoticeAdvance")String eventNoticeAdvance) throws Exception{ 
     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String updateDeviceStatement = "UPDATE dbo.Devices SET dueDateNotice="+dueDateNotice+", dueDateNoticeAdvance="+dueDateNoticeAdvance 
            +", holdsNotice="+holdsNotice+", eventNoticeAdvance="+eventNoticeAdvance+" WHERE deviceID='"+deviceID+"'"; 
     Statement state = c.createStatement(); 
     state.executeUpdate(updateDeviceStatement); 

     return "true"; 
    } 


    @Path("/removeUser") 
    @GET 

    public String removeUser(@QueryParam("cardNumber")String cardNumber) throws Exception{ 
     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String removeStatement = "DELETE FROM dbo.Patron WHERE cardNumber='"+cardNumber+"'"; 

     Statement state = c.createStatement(); 
     state.executeUpdate(removeStatement); 




     return "true"; 
    } 

    @Path("/addEvent") 
    @GET 

    public String addEvent(@QueryParam("deviceID")String deviceID, @QueryParam("eventID")String eventID) throws Exception{ 

     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String eventStatement = "INSERT INTO dbo.Events VALUES ('"+deviceID+"','"+eventID+"')"; 
     Statement state = c.createStatement(); 
     state.executeUpdate(eventStatement); 


     return "true"; 
    } 

    @Path("/removeEvent") 
    @GET 

    public String removeEvent(@QueryParam("deviceID")String deviceID, @QueryParam("eventID")String eventID) throws Exception{ 

     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String eventStatement = "DELETE FROM dbo.Events WHERE deviceID='"+deviceID+"' AND eventID='"+eventID+"'"; 
     Statement state = c.createStatement(); 
     state.executeUpdate(eventStatement); 


     return "true"; 
    } 

    @Path("/removeAllEvents") 
    @GET 

    public String removeAllEvents(@QueryParam("deviceID")String deviceID) throws Exception{ 

     String connectionUrl = "jdbc:sqlserver://mssql.acpl.lib.in.us:1433;" + 
        "databaseName=MobileNotify;user=Mobile_Notification_User;password=xxxx;"; 


     Connection c = DriverManager.getConnection(connectionUrl); 

     String eventStatement = "DELETE FROM dbo.Events WHERE deviceID='"+deviceID+"'"; 
     Statement state = c.createStatement(); 
     state.executeUpdate(eventStatement); 


     return "true"; 
    } 
} 

這是我的web.xml文件：

<?xml version="1.0" encoding="UTF-8"?> 
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> 
    <display-name>APNS_WebService</display-name> 
    <servlet> 
     <servlet-name>javax.ws.rs.core.Application</servlet-name> 
     <load-on-startup>1</load-on-startup> 
    </servlet> 
    <servlet-mapping> 
     <servlet-name>javax.ws.rs.core.Application</servlet-name> 
     <url-pattern>/rest/*</url-pattern> 
    </servlet-mapping> 
</web-app> 

讓我知道，如果需要了解更多信息！

Answer 1

我相信您的NPE的原因是您的<servlet>區塊中缺少<servlet-class>元素。然而，決定什麼servlet類應該引發更大的問題......

看起來你沒有選擇JAX-RS框架。請參閱JAX-RS Frameworks瞭解各種備選方案。

我目前使用澤西島。澤西島一個典型的web.xml文件可能包含：

<servlet> 
    <servlet-name>WebService</servlet-name> 
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class> 
    <init-param> 
     <param-name>com.sun.jersey.config.property.packages</param-name> 
     <param-value>webservice</param-value> 
    </init-param> 
    <init-param> 
     <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name> 
     <param-value>true</param-value> 
    </init-param> 
    <load-on-startup>1</load-on-startup> 
    </servlet> 

    <servlet-mapping> 
    <servlet-name>WebService</servlet-name> 
    <url-pattern>/api/rest/*</url-pattern> 
    </servlet-mapping> 

對於很多JAX-RS的框架，框架的選擇將決定你應該進入什麼爲<servlet-class>

還要注意，由於你的根資源是包webservice，我將com.sun.jersey.config.property.packages參數設置爲webservice，以便Jersey將掃描您的包以查找任何JAX-RS註釋類。