NullPointerException使我疯了

Question

编写一个UPnP控制点应用程序。但是我一直得到一个nullpointerexception： 这里的第一个代码是导致npe的原因。以粗体显示，调用createAbsoluteURL。其余的都是不同的类（URIUtil）内的方法，抱着createAbsoluteURL不同的呼叫/ URI

content = new MediaStoreContent(
        context, 
        **new URLBuilder() { 
         public String getURL(DIDLObject object) { 
          return URIUtil.createAbsoluteURL(
            addy, 
            getHttpServerService().getLocalPort(), 
            URI.create("/" + object.getId()) 
          ).toString(); 
         }** 

         public String getObjectId(String urlPath) { 
          return urlPath.substring(1); // Cut the slash 
         } 
        } 
      ); 



public static URL createAbsoluteURL(InetAddress address, int localStreamPort, URI relativeOrNot) throws IllegalArgumentException { 
     try { 
      if (address instanceof Inet6Address) { 
       return createAbsoluteURL(new URL("http://[" + address.getHostAddress() + "]:" + localStreamPort), relativeOrNot); 
      } else if (address instanceof Inet4Address) { 
       return createAbsoluteURL(new URL("http://" + address.getHostAddress() + ":" + localStreamPort), relativeOrNot); 
      } else { 
       throw new IllegalArgumentException("InetAddress is neither IPv4 nor IPv6: " + address); 
      } 
     } catch (Exception ex) { 
      throw new IllegalArgumentException("Address, port, and URI can not be converted to URL", ex); 
     } 
    } 

public static URL createAbsoluteURL(URL base, URI relativeOrNot) throws IllegalArgumentException { 

     if (base == null && !relativeOrNot.isAbsolute()) { 
      throw new IllegalArgumentException("Base URL is null and given URI is not absolute"); 
     } else if (base == null && relativeOrNot.isAbsolute()) { 
      try { 
       return relativeOrNot.toURL(); 
      } catch (Exception ex) { 
       throw new IllegalArgumentException("Base URL was null and given URI can't be converted to URL"); 
      } 
     } else { 
      try { 
       assert base != null; 
       URI baseURI = base.toURI(); 
       URI absoluteURI = createAbsoluteURI(baseURI, relativeOrNot); 
       return absoluteURI.toURL(); 
      } catch (Exception ex) { 
       throw new IllegalArgumentException(
         "Base URL is not an URI, or can't create absolute URI (null?), " + 
           "or absolute URI can not be converted to URL", ex); 
      } 
     } 
    } 



public static URI createAbsoluteURI(URI base, URI relativeOrNot) throws IllegalArgumentException { 
      if (base == null && !relativeOrNot.isAbsolute()) { 
       throw new IllegalArgumentException("Base URI is null and given URI is not absolute"); 
      } else if (base == null && relativeOrNot.isAbsolute()) { 
       return relativeOrNot; 
      } else { 
       assert base != null; 
       // If the given base URI has no path we give it a root path 
       if (base.getPath().length() == 0) { 
        try { 
         base = new URI(base.getScheme(), base.getAuthority(), "/", base.getQuery(), base.getFragment()); 
        } catch (Exception ex) { 
         throw new IllegalArgumentException(ex); 
        } 
       } 
       return base.resolve(relativeOrNot); 
      } 
     } 

这是我的日志：

E/AndroidRuntime(9824): Caused by: java.lang.NullPointerException 
E/AndroidRuntime(9824):  at org.teleal.cling.android.browser.MediaServerS 
erviceImpl$ContentHttpServerConnection.<init>(MediaServerServiceImpl.java:159) 
E/AndroidRuntime(9824):  at org.teleal.cling.android.browser.MediaServerS 
erviceImpl.onCreate(MediaServerServiceImpl.java:72) 
E/AndroidRuntime(9824):  at android.app.ActivityThread.handleCreateServic 
e(ActivityThread.java:2959) 
E/AndroidRuntime(9824):  ... 10 more 

Answer 1

至少有两件事情可以为空，并导致NPE在部分高亮显示您：

• getHttpServerService()
• object

您确定您的对象在该方法被调用之前已被初始化？