SNMP4J 源码包中的使用说明

SNMP4J 是 APACHE 的一个开源项目,为 SNMP 的编程提供了一个很好的框架.支持 SNMPv1, v2c, v3 版本.既可以编写客户端程序,也可以编写服务器端程序.

没有时间翻译它,就直接把它贴了上来.英文很简单,例子都很直观,不看英文直接看代码也没什么问题.

以下是 org.snmp4j 包下的说明

Provides classes and interfaces for creating, sending, and receiving SNMP messages.

The 

org.snmp4j

 classes are capable of creating, sending, and receiving SNMPv1/v2c/v3 messages. A SNMP message is composed of its message header and its PDU
payload. This package contains three main groups of classes and interfaces:

Classes for SNMP message and target creation

Classes for SNMP message sending (command generation)

Classes for SNMP message dispatching (command responding)

The following UML package diagram illustrates the dependencies between the packages of the core SNMP4J API. Users of the API normally only need to use the 

org.snmp4j

 and
the 

org.snmp4j.smi

 packages directly.



 

The following UML class diagram shows the most important classes of the org.snmp4j package and their relationships (relationships to other packages are not shown):.

SNMP Messages and Targets

To exchange a SNMP message with a remote system, that system has to be identified, retransmission, and timeout policy information about the message exchange has to be specified. A remote system is specified with SNMP4J by creating a 

Target

 instance
appropriate for the SNMP protocol to be used.

For SNMPv1 and SNMPv2c the 

CommunityTarget

 has to be used which provides community information in addition to the address, retransmission, and timeout policy
information defined by the 

Target

 interface.

For SNMPv3 the 

UserTarget

 has to be used instead. It extends the 

SecureTarget

 abstract
class and provides the following User Based Security Model (USM) user information: security name, security level, security model (i.e. USM), and authoritative engine ID.

A SNMP message consists of the message's payload, the SNMP Protocol Data Unit (PDU) and a message header. Simplified said, in SNMP4J the message header information is represented by 

Target

 instances
and the PDU is represented by one of the following classes:

PDUv1

 (SNMPv1)

PDU

 (SNMPv2c)

ScopedPDU

 (SNMPv3)

Thus, in order to be able to send a SNMP message with SNMP4J, a 

PDU

 instance and a 

Target

 instance
have to be created.

PDU Examples (PDU 使用的例子)

SNMPv1/v2c GETNEXT PDU

import org.snmp4j.PDU;
import org.snmp4j.smi.*;
...
PDU pdu = new PDU();
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.1"))); // sysDescr
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.1"))); // ifNumber
pdu.setType(PDU.GETNEXT);
...

SNMPv3 GETBULK PDU

import org.snmp4j.ScopedPDU;
import org.snmp4j.smi.*;
...
ScopedPDU pdu = new ScopedPDU();
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.1"))); // ifNumber
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.10"))); // ifInOctets
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.16"))); // ifOutOctets
pdu.setType(PDU.GETBULK);
pdu.setMaxRepetitions(50);
// Get ifNumber only once
pdu.setNonRepeaters(1);
// set context non-default context (default context does not need to be set)
pdu.setContextName(new OctetString("subSystemContextA"));
// set non-default context engine ID (to use targets authoritative engine ID
// use an empty (size == 0) octet string)
pdu.setContextEngineID(OctetString.fromHexString("80:00:13:70:c0:a8:01:0d"));
...

SNMPv1 TRAP PDU ()

import org.snmp4j.PDUv1;
...
PDUv1 pdu = new PDUv1();
pdu.setType(PDU.V1TRAP);
pdu.setGenericTrap(PDUv1.COLDSTART);
...

SNMPv2c/SNMPv3 INFORM PDU

import org.snmp4j.ScopedPDU;
...
ScopedPDU pdu = new ScopedPDU();
pdu.setType(PDU.INFORM);
// sysUpTime
long sysUpTime = (System.currentTimeMillis() - startTime) / 10;
pdu.add(new VariableBinding(SnmpConstants.sysUpTime, new TimeTicks(sysUpTime)));
pdu.add(new VariableBinding(SnmpConstants.snmpTrapOID, SnmpConstants.linkDown));
// payload
pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.1"+downIndex),
new Integer32(downIndex)));
...

Target Examples (对象例子)

Community Target

CommunityTarget target = new CommunityTarget();
target.setCommunity(new OctetString("public"));
target.setAddress(targetAddress);
target.setVersion(SnmpConstants.version1);

User Target

UserTarget target = new UserTarget();
target.setAddress(targetAddress);
target.setRetries(1);
// set timeout to 500 milliseconds -> 2*500ms = 1s total timeout
target.setTimeout(500);
target.setVersion(SnmpConstants.version3);
target.setSecurityLevel(SecurityLevel.AUTH_PRIV);
target.setSecurityName(new OctetString("MD5DES"));

Sending SNMP messages

SNMP message are sent with SNMP4J by using a instance of the SNMP 

Session

 interface. The default implementation of this interface is the 

Snmp

class.

To setup a 

Snmp

 instance it is sufficient to call its constructor with a 

TransportMapping

 instance.
The transport mapping is used by the SNMP session to send (and receive) SNMP message to a remote systems by using a transport protocol, for example the User Datagram Protocol (UDP).

A SNMP4J 

Snmp

 instance supports SNMP v1, v2c, and v3 by default. By sub-classing 

Snmp

 other
combinations of those SNMP protocol versions can be supported.

With SNMP4J, SNMP messages can be sent synchronously (blocking) and asynchronously (non-blocking). The 

Snmp

 class
does not use an internal thread to process responses on asynchronous and synchronous requests. Nevertheless it uses the receiver threads of the transport mappings to process responses.

Asynchronous responses are returned by calling a callback method on an object instance that implements the 

ResponseListener

 interface. The callback is carried
out on behalf of the transport mapping thread that received the response packet from the wire. Thus, if the called method blocks, the delivery of synchronous and asynchronous messages received on the listen port of that transport mapping will be also blocked.
Other transport mapping will not be affected. Blocking can be avoided by either using synchronous messages only or by decoupling the processing within the callback method.

Example for Sending a Synchronous Message (发送同步消息)

import org.snmp4j.*;
...
Snmp snmp = new Snmp(new DefaultUdpTransportMapping());
...
ResponseEvent response = snmp.send(requestPDU, target);
if (response.getResponse() == null) {
// request timed out
...
}
else {
System.out.println("Received response from: "+
response.getPeerAddress());
// dump response PDU
System.out.println(response.getResponse().toString());
}

Example for Sending an Asynchronous Message (发送异步消息)

import org.snmp4j.*;
import org.snmp4j.event.*;
...
Snmp snmp = new Snmp(new DefaultUdpTransportMapping());
...
ResponseListener listener = new ResponseListener() {
public void onResponse(ResponseEvent event) {
PDU response = event.getResponse();
PDU request = event.getRequest();
if (response == null) {
System.out.println("Request "+request+" timed out");
}
else {
System.out.println("Received response "+response+" on request "+
request);
}
};
snmp.sendPDU(request, target, null, listener);
...

Receiving SNMP messages(接收SNMP信息)

SNMP4J receives SNMP messages through the listen port of transport mappings. In order to be able to receive responses or requests, that port needs to be set into listen mode. This has to be done by calling the 

listen()

 method
of the 

TransportMapping

 instance to start the transport mappings internal listen thread. The internal thread is stopped and the listen port is closed by calling
the 

close()

 method on the

TransportMapping

 instance or
the associated 

Snmp

 instance.

The transport mapping just receives the SNMP mesage as a stream of bytes and forwards the message to associated 

MessageDispatcher

 instances. By default, SNMP4J
uses one instance of the 

MessageDispatcherImpl

 class for decoding and dispatching incoming messages. That instance is created and used internally by the 

Snmp

 class.

The 

Snmp

 class processes responses to outstanding requests and forwards PDUs of other SNMP messages to registered 

CommandResponder

 listener
instances. To receive SNMP messages it is thus sufficient to

Create a 

TransportMapping

 and initialize its listen port by calling 

TransportMapping.listen()

.

Create a 

Snmp

 instance with the above 

TransportMapping

.

Instantiate a class that implements the 

CommandResponder

 interface and register it with the 

Snmp

 instance
by calling

Snmp.addCommandResponder(CommandResponder)

.

When a unhandled SNMP message (thus a SNMP message where no corresponding outstanding request exists) is received, then the

processPdu(CommandResponderEvent)

 method
of the 

CommandResponder

 will be called with the decoded PDU and additional information about the received SNMP message provided by the message processing model
that has decoded the SNMP message.

Example for Receiving SNMP Messages (接收SNMP消息的例子)

import org.snmp4j.*;
import org.snmp4j.smi.*;
import org.snmp4j.mp.SnmpConstants;
...
TransportMapping transport =
new DefaultUdpTransportMapping(new UdpAddress("0.0.0.0/161"));
Snmp snmp = new Snmp(transport);
if (version == SnmpConstants.version3) {
byte[] localEngineID =
((MPv3)snmp.getMessageProcessingModel(MessageProcessingModel.MPv3)).createLocalEngineID();
USM usm = new USM(SecurityProtocols.getInstance(),
new OctetString(localEngineID), 0);
SecurityModels.getInstance().addSecurityModel(usm);
snmp.setLocalEngine(localEngineID, 0, 0);
// Add the configured user to the USM
...
}
snmp.addCommandResponder(this);
transport.listen();
...
public synchronized void processPdu(CommandResponderEvent e) {
PDU command = e.getPdu();
if (command != null) {
...
}
}

以下是 org.snmp4j.smi 包下的说明:

Provides classes for the representation of SMIv1/v2 data types (which also includes some basic ASN.1 primitive data types).

The

org.snmp4j.smi

classes are capable of BER encoding and decoding themself to/from a byte stream. In addition, the SMI data type classes provide convenient functions for manipulating their content. The

VariantVariable

is a special class that can be used in command responder applications to intercept access to a SMI value.

Variable Binding Examples

import org.snmp4j.smi.*;
...
VariableBinding vb = new VariableBinding(new OID("1.3.6.1.2.1.1.4.0"));
vb.setValue(new OctetString("SNMP4J Text"));
...
vb = new VariableBinding();
vb.setOid(new OID(new int[] { 1,3,6,1,2,1,1,2,0 }));
...
vb = new VariableBinding(vb.getOid(), new IpAddress("255.255.255.255"));
...
vb = new VariableBinding(vb.getOid(), new Gauge32(2^32-1));
int syntax = vb.getSyntax();
if (syntax != SMIConstants.SYNTAX_GAUGE32) {
// never reached
}
else {
long value = ((UnsignedInteger32)vb.getValue()).getValue();
System.out.println(vb.getOid() + " = " + value);
// prints: 1.3.6.1.2.1.1.2.0 = 4294967295
}
...

The following UML class diagram shows the most important classes of the

org.snmp4j.smi

package and their relationships (relationships to other packages are not shown): UML类图

以下是 org.snmp.asn1 包中的说明

Provides classes and interfaces for the mapping between Abstract Syntax Notation One (ASN.1) formatted values and their transfer syntax according to the Basic Encoding Rules (BER).

The

org.snmp4j.asn1

classes are capable of serializing of ASN.1 formatted values into a byte stream and deserializing the same from a byte stream. There are three groups of classes/interfaces in this package: The

BER

class implements the BER serialization and deserialization by providing static methods for encoding/decoding of primitive ASN.1 and Structure of Management Information (SMI) data types.
The

BERSerializable

interface provides a common interface for all objects that are (de)serializable according to the Basic Encoding Rules (BER).
The

BERInputStream

and the

BEROutputStream

provide optimized implementations for the serialization and deserialization of the

InputStream

and

OutputStream

abstract classes.
The following UML class diagram shows the most important classes of the

org.snmp4j.asn1

package and their relationships (relationships to other packages are not shown): 以下是 org.snmp4j.mp 包中的说明

Provides classes and interfaces for the SNMP message processing.

The

org.snmp4j.mp

classes provide services to process SNMP messages. The services provided are defined in the

MessageProcessingModel

interface and include the following: Prepare data elements from an incoming SNMP message as described in RFC3412 §7.2.
Prepare a response message as defined in RFC3412 §7.1.
Prepare an outgoing message as defined in RFC3412 §7.1.
This interface is implemented by the message processing model classes for the SNMP versions 1, v2c, and v3:

MPv1

,

MPv2c

, and

MPv3

. The

MessageDispatcherImpl

chooses which message processing model it uses to process an outgoing or incoming SNMP message based on the SNMP version of the message. The SNMP version is either extracted from the message header (incoming message) or from the

Target

instance associated with the outgoing PDU (ougoing message). To be able to match requests and responses SNMP uses request IDs. Since request IDs are created by the command generator, the request IDs are unique within such a command generator only. SNMP4J therefore has to abstract from request IDs and uses

PduHandle

instances instead. If a

PDU

is processed for sending by the SNMP4J

MessageDispatcherImpl

and the PDU's request ID is set to 0, then a SNMP4J application wide unique ID is generated and set as request ID of the supplied PDU. In any case, the PDU's request ID will be used as transaction ID of the outgoing message. The transaction ID identifies a messages

PduHandle

. If a

PDU

is received by the SNMP4J

MessageDispatcherImpl

a unique transaction ID is generated so that command responders as well as the message processing model can match requests and responses. The following UML class diagram shows the most important classes of the

org.snmp4j.mp

package and their relationships (relationships to other packages are not shown): 以下是 org.snmp4j.transport 包中的说明

Provides transport protocol mappings for SNMP.

The

org.snmp4j.transport

classes are capable of sending and receiving byte messages to and from a network using transport mapping specific transport protocol. All SNMP4J transport mappings have to implement the

org.snmp4j.TransportMapping

interface. SNMP4J supports two transport mappings for the transport protocols UDP and TCP: The UDP transport mapping is the default SNMP transport mapping. It is implemented by the

DefaultUdpTransportMapping

class.
The TCP transport mapping is implemented by the

DefaultTcpTransportMapping

using the

java.nio

package.
Additional transport mappings can be easily added. It is sufficient to implement the

org.snmp4j.TransportMapping

interface and add an instance of that class to the

Snmp

(or

MessageDispatcher

) object. To be able to lookup a transport mapping by an

Address

class via the

TransportMappings

(as

Snmp

does for notification listeners), a transport mapping has to be registered in a transport mapping registration file. The default file is

transports.properties

in the

org.snmp4j.transport

package. To use a different file, set the system property

org.snmp4j.transportMappings

. Connection-oriented transport mappings like TCP should implement the

ConnectionOrientedTransportMapping

interface to support

MessageLengthDecoder

and

TransportStateListener

.The following UML class diagram shows the classes of the

org.snmp4j.transport

package and their relationships (relationships to other packages are not shown): 以下是 org.snmp4j.util 包中的说明

Contains table retrieval utilities and multi-threading support classes as well as miscellaneous utility classes.

The

org.snmp4j.util

contains the following groups of classes: Classes for SNMP table retrieval. The class

TableUtils

can be used to asynchronously retrieve table data effeciently row by row.
Classes for support of multi-threaded message dispatching. The class

MultiThreadedMessageDispatcher

implements the

MessageDispatcher

interface and uses the

MessageDispatcherImpl

class to dispatch incoming message using the threads of a

ThreadPool

.
The following UML class diagram shows the classes of the

org.snmp4j.util

package and their relationships (relationships to other packages are not shown): 在 SNMP4J 包中还有多线程的东东,主要用于服务器端.文档里没写,去看 API 吧,里面有绍.