android - Android 版

Question

我想在 android 中使用简单的 snmp get。我找到了 java 的代码并尝试在 android 中使用它。我还附加了 snmp4j.jar 文件用于 android。但是我得到了 NullPointer 异常，我没有得到输出。如果有人对如何在 android 中使用 snmp 有任何想法或代码，请给我建议。

以下是我试过的代码，

1   import java.io.IOException;
2   import org.snmp4j.CommunityTarget;
3   import org.snmp4j.PDU;
4   import org.snmp4j.Snmp;
5   import org.snmp4j.TransportMapping;
6   import org.snmp4j.event.ResponseEvent;
7   import org.snmp4j.mp.SnmpConstants; 
8   import org.snmp4j.smi.OID;
9   import org.snmp4j.smi.OctetString;
10  import org.snmp4j.smi.UdpAddress;
11  import org.snmp4j.smi.VariableBinding;
12  import org.snmp4j.transport.DefaultUdpTransportMapping;
13  import android.app.Activity;
14  import android.os.Bundle;
15  import android.util.Log;
16  import android.view.View;
17  import android.view.View.OnClickListener;
18  import android.widget.Button;
19  import android.widget.Toast;
20 
21  public class SNMPClient extends Activity {
22
23  private static String ipAddress = "127.0.0.1";
24  private static String port = "161";
25  //cmd to request from Server
26  private static String oidValue = "1.3.6.1.2.1.1.5.0";
27  private static int snmpVersion = SnmpConstants.version2c;
28  private static String community = "public";
29 
30  public static Snmp snmp;
31  public static CommunityTarget comtarget;
32  static PDU pdu;
33  static OID oid;
34  static VariableBinding req;
35  Button b;
36  private static final String tag = "SNMP CLIENT";
37
38 @Override
39 public void onCreate(Bundle savedInstanceState) {
40    super.onCreate(savedInstanceState);
41    setContentView(R.layout.main);
42    
43    System.setProperty("java.net.preferIPv4Stack", "true");
44      System.setProperty("java.net.preferIPv6Addresses", "false");
45      
46    b = (Button) findViewById(R.id.getvalue);
47    b.setOnClickListener(new OnClickListener() {
48
49        public void onClick(View v) {
50            // TODO Auto-generated method stub
51           try {
52                sendSnmpRequest(oidValue);
53            } catch (IOException e) {
54                // TODO Auto-generated catch block
55                e.printStackTrace();
56            } catch (Exception e) {
57                // TODO Auto-generated catch block
58                e.printStackTrace();
59            }
60
61        }
62    });
63   }
64 
65 private void sendSnmpRequest(String cmd) throws Exception {
66    // Create TransportMapping and Listen
67    TransportMapping transport = new DefaultUdpTransportMapping();
68    transport.listen();
69 
70    // Create Target Address object
71    CommunityTarget comtarget = new CommunityTarget();
72    comtarget.setCommunity(new OctetString(community));
73    comtarget.setVersion(snmpVersion);
74    comtarget.setAddress(new UdpAddress(ipAddress + "/" + port));
75    comtarget.setRetries(2);
76    comtarget.setTimeout(1000);
77    // Prepare PDU
78    req = new VariableBinding();
79    OID oid = new OID(cmd);   
80    req.setOid(oid);
81    pdu = new PDU();
82    pdu.add(req);
83    Snmp snmp = new Snmp(transport);
84    Log.i(tag ,"Sending Request to Agent...");
85    ResponseEvent response = snmp.get(pdu, comtarget);
86    // Process Agent Response
87    if (response != null) {
88        Log.i(tag,"Got Response from Agent");   //upto  this get in Logcat 
89        PDU responsePDU = response.getResponse();  //Here get Null response
90        if (responsePDU != null) {
91            int errorStatus = responsePDU.getErrorStatus();
92            int errorIndex = responsePDU.getErrorIndex();
93            String errorStatusText = responsePDU.getErrorStatusText();
94 
95            if (errorStatus == PDU.noError) {
96                Log.i(tag,"Snmp Get Response = "
97                        + responsePDU.getVariableBindings());
98                Toast.makeText(getApplicationContext(),
99                     "Snmp Get Response = " + responsePDU.getVariableBindings(),Toast.LENGTH_LONG).show();
100            } else {
101                 Log.i((String) tag,"Error: Request Failed");
102                 Log.i(tag,"Error Status = " + errorStatus);
103                 Log.i(tag,"Error Index = " + errorIndex);
104                 Log.i(tag,"Error Status Text = " + errorStatusText);
105             }
106         } else {
107             Log.i(tag,"Error: Response PDU is null");  // This get in Logcat
108         }
109     } else {
110         Log.i(tag,"Error: Agent Timeout... ");
111     }
112     snmp.close();
113 }}

请任何人有任何解决方案请建议我。提前致谢......

在第 89 行获取空值，因此获取 NUllPointer 异常......任何想法或代码

Answer 1

来自ResponseEvent.getResponse()文档(强调我的):

Returns: a PDU instance if a response has been received. If the request timed out then null will be returned.

现在显然您可以看到您在该行得到了 null 响应:

PDU responsePDU = response.getResponse();

最有可能因为您正尝试通过 SNMP 获取 Android 的本地主机地址，即:

private static String ipAddress = "127.0.0.1";
private static String port = "161";
// ...
comtarget.setAddress(new UdpAddress(ipAddress + "/" + port));

这没有意义，因为您的 Android 可能没有本地运行的 SNMP 服务，那么您如何从未运行的 SNMP 服务获得响应？

尝试将 ipAddress 更改为您要连接的设备的地址。