androidpn的学习研究（六）Androidpn-server的Mina编码和解码解析过程

          在许多网络应用中可能针对传输的数据进行加密操作，接收到数据之后进行解码操作。

在mina中提供许多加密和解密的解析方式：

1.带一定前缀的字符串的解析方式。

2.序列化对象的字符串解析方式。

3.分隔符方式的字符串解析方式。

在mina中提供相关的filterchain支持相关的操作。

Mina的源代码如下：

package org.apache.mina.filter.codec;

import org.apache.mina.core.session.IoSession;

/**
 * Provides {@link ProtocolEncoder} and {@link ProtocolDecoder} which translates
 * binary or protocol specific data into message object and vice versa.
 * <p>
 * Please refer to
 * <a href="../../../../../xref-examples/org/apache/mina/examples/reverser/ReverseProtocolProvider.html"><code>ReverserProtocolProvider</code></a>
 * example.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public interface ProtocolCodecFactory {
    /**
     * Returns a new (or reusable) instance of {@link ProtocolEncoder} which
     * encodes message objects into binary or protocol-specific data.
     */
    ProtocolEncoder getEncoder(IoSession session) throws Exception;

    /**
     * Returns a new (or reusable) instance of {@link ProtocolDecoder} which
     * decodes binary or protocol-specific data into message objects.
     */
    ProtocolDecoder getDecoder(IoSession session) throws Exception;
}

加密处理类：

package org.apache.mina.filter.codec;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;

/**
 * Encodes higher-level message objects into binary or protocol-specific data.
 * MINA invokes {@link #encode(IoSession, Object, ProtocolEncoderOutput)}
 * method with message which is popped from the session write queue, and then
 * the encoder implementation puts encoded messages (typically {@link IoBuffer}s)
 * into {@link ProtocolEncoderOutput} by calling {@link ProtocolEncoderOutput#write(Object)}.
 * <p>
 * Please refer to
 * <a href="../../../../../xref-examples/org/apache/mina/examples/reverser/TextLineEncoder.html"><code>TextLineEncoder</code></a>
 * example.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 * 
 * @see ProtocolEncoderException
 */
public interface ProtocolEncoder {

    /**
     * Encodes higher-level message objects into binary or protocol-specific data.
     * MINA invokes {@link #encode(IoSession, Object, ProtocolEncoderOutput)}
     * method with message which is popped from the session write queue, and then
     * the encoder implementation puts encoded messages (typically {@link IoBuffer}s)
     * into {@link ProtocolEncoderOutput}.
     *
     * @throws Exception if the message violated protocol specification
     */
    void encode(IoSession session, Object message, ProtocolEncoderOutput out)
            throws Exception;

    /**
     * Releases all resources related with this encoder.
     *
     * @throws Exception if failed to dispose all resources
     */
    void dispose(IoSession session) throws Exception;
}

解密类如下：

package org.apache.mina.filter.codec;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;

/**
 * Decodes binary or protocol-specific data into higher-level message objects.
 * MINA invokes {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
 * method with read data, and then the decoder implementation puts decoded
 * messages into {@link ProtocolDecoderOutput} by calling
 * {@link ProtocolDecoderOutput#write(Object)}.
 * <p>
 * Please refer to
 * <a href="../../../../../xref-examples/org/apache/mina/examples/reverser/TextLineDecoder.html"><code>TextLineDecoder</code></a>
 * example.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 * 
 * @see ProtocolDecoderException
 */
public interface ProtocolDecoder {
    /**
     * Decodes binary or protocol-specific content into higher-level message objects.
     * MINA invokes {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
     * method with read data, and then the decoder implementation puts decoded
     * messages into {@link ProtocolDecoderOutput}.
     *
     * @throws Exception if the read data violated protocol specification
     */
    void decode(IoSession session, IoBuffer in, ProtocolDecoderOutput out)
            throws Exception;

    /**
     * Invoked when the specified <tt>session</tt> is closed.  This method is useful
     * when you deal with the protocol which doesn't specify the length of a message
     * such as HTTP response without <tt>content-length</tt> header. Implement this
     * method to process the remaining data that {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
     * method didn't process completely.
     *
     * @throws Exception if the read data violated protocol specification
     */
    void finishDecode(IoSession session, ProtocolDecoderOutput out)
            throws Exception;

    /**
     * Releases all resources related with this decoder.
     *
     * @throws Exception if failed to dispose all resources
     */
    void dispose(IoSession session) throws Exception;
}

在androidpn中的没有采取任何加密方式，但是提供相关的类org.androidpn.server.xmpp.codec，如果需要可以针对传输的数据进行加密和解密工作。

package org.androidpn.server.xmpp.codec;

import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolCodecFactory;
import org.apache.mina.filter.codec.ProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolEncoder;

/** 
 * Factory class that specifies the encode and decoder to use for parsing XMPP stanzas.
 *
 * @author Sehwan Noh ([email protected])
 */
public class XmppCodecFactory implements ProtocolCodecFactory {

    private final XmppEncoder encoder;

    private final XmppDecoder decoder;

    /**
     * Constructor.
     */
    public XmppCodecFactory() {
        encoder = new XmppEncoder();
        decoder = new XmppDecoder();
    }

    /**
     * Returns a new (or reusable) instance of ProtocolEncoder.
     */
    public ProtocolEncoder getEncoder(IoSession session) throws Exception {
        return encoder;
    }

    /**
     * Returns a new (or reusable) instance of ProtocolDecoder.
     */
    public ProtocolDecoder getDecoder(IoSession session) throws Exception {
        return decoder;
    }

}

androidpn的解密类：

package org.androidpn.server.xmpp.codec;

import org.androidpn.server.xmpp.net.XmppIoHandler;
import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.CumulativeProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;
import org.jivesoftware.openfire.nio.XMLLightweightParser;

/** 
 * Decoder class that parses ByteBuffers and generates XML stanzas.
 *
 * @author Sehwan Noh ([email protected])
 */
public class XmppDecoder extends CumulativeProtocolDecoder {

    // private final Log log = LogFactory.getLog(XmppDecoder.class);

    @Override
    public boolean doDecode(IoSession session, IoBuffer in,
            ProtocolDecoderOutput out) throws Exception {
        // log.debug("doDecode(...)...");

        XMLLightweightParser parser = (XMLLightweightParser) session
                .getAttribute(XmppIoHandler.XML_PARSER);
        parser.read(in);

        if (parser.areThereMsgs()) {
            for (String stanza : parser.getMsgs()) {
                out.write(stanza);
            }
        }
        return !in.hasRemaining();
    }

}

androidpn的加密类：

package org.androidpn.server.xmpp.codec;

import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolEncoder;
import org.apache.mina.filter.codec.ProtocolEncoderOutput;

/** 
 *  Encoder class that does nothing (to the already encoded data). 
 *
 * @author Sehwan Noh ([email protected])
 */
public class XmppEncoder implements ProtocolEncoder {

    // private final Log log = LogFactory.getLog(XmppEncoder.class);

    public void encode(IoSession session, Object message,
            ProtocolEncoderOutput out) throws Exception {
        // log.debug("encode()...");
    }

    public void dispose(IoSession session) throws Exception {
        // log.debug("dispose()...");
    }

}

   最终将编码解析器转换为过滤器使用，具体配置如下：

<bean class="org.apache.mina.filter.codec.ProtocolCodecFilter">
						<constructor-arg>
							<bean class="org.androidpn.server.xmpp.codec.XmppCodecFactory" />
						</constructor-arg>
					</bean>