最近在研读Mina框架的源码,刚好手头上有项目就直接用上了。直接进入正题……
对Mina有点了解的人都知道,Mina中有一条FilterChain,我们可以向其中加入Filter实现链式处理。从源码看来,多数Filter(如ProtocolCodecFilter)在使用过程只允许有一个实例。若FilterChain中存在多个相同的实例,则有可能出现各种莫明其妙的问题,这些问题往往是超出你预料之外的,而且调试起来比较困难,除非你熟知Mina整个框架。究其原因,主要是在AttributeKey的问题,例:
public class ProtocolCodecFilter extends IoFilterAdapter { /** A logger for this class */ private static final Logger LOGGER = LoggerFactory.getLogger(ProtocolCodecFilter.class); private static final Class<?>[] EMPTY_PARAMS = new Class[0]; private static final IoBuffer EMPTY_BUFFER = IoBuffer.wrap(new byte[0]); private final AttributeKey ENCODER = new AttributeKey(ProtocolCodecFilter.class, "encoder"); private final AttributeKey DECODER = new AttributeKey(ProtocolCodecFilter.class, "decoder"); private final AttributeKey DECODER_OUT = new AttributeKey(ProtocolCodecFilter.class, "decoderOut"); private final AttributeKey ENCODER_OUT = new AttributeKey(ProtocolCodecFilter.class, "encoderOut"); ... private ProtocolDecoderOutput getDecoderOut(IoSession session, NextFilter nextFilter) { ProtocolDecoderOutput out = (ProtocolDecoderOutput) session.getAttribute(DECODER_OUT); if (out == null) { // Create a new instance, and stores it into the session out = new ProtocolDecoderOutputImpl(); session.setAttribute(DECODER_OUT, out); } return out; } ... }
ProtocolDecoderOutput out = (ProtocolDecoderOutput) session.getAttribute(DECODER_OUT);
它们获取的实例是一样的。因此,也就造成两个实例中的ProtocolCodecOutput产生相互干扰的情况。
我们再来看看为什么两个实例中的AttributeKey为什么会是一样的。
package org.apache.mina.core.session; import java.io.Serializable; /** * Creates a Key from a class name and an attribute name. The resulting Key will * be stored in the session Map.<br> * For instance, we can create a 'processor' AttributeKey this way : * * <pre> * private static final AttributeKey PROCESSOR = new AttributeKey( * SimpleIoProcessorPool.class, "processor"); * </pre> * * This will create the <b>SimpleIoProcessorPool.processor@7DE45C99</b> key * which will be stored in the session map.<br> * Such an attributeKey is mainly useful for debug purposes. * * @author <a href="http://mina.apache.org">Apache MINA Project</a> */ public final class AttributeKey implements Serializable { /** The serial version UID */ private static final long serialVersionUID = -583377473376683096L; /** The attribute's name */ private final String name; public AttributeKey(Class<?> source, String name) { this.name = source.getName() + '.' + name + '@' + Integer.toHexString(this.hashCode()); } @Override public String toString() { return name; } @Override public int hashCode() { int h = 17 * 37 + ((name == null) ? 0 : name.hashCode()); return h; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (!(obj instanceof AttributeKey)) { return false; } AttributeKey other = (AttributeKey) obj; return name.equals(other.name); } }session.getAttrubute(...) 中存储<KEY, VALUE>对的其实是
private static class DefaultIoSessionAttributeMap implements IoSessionAttributeMap { private final ConcurrentHashMap<Object, Object> attributes = new ConcurrentHashMap<Object, Object>(4); ... }
我们看到AttributeKey的hashCode()函数,唯一不一样的地方就只能是name,name是String类型的,其hashCode()计算方法如下:
Open Declaration int java.lang.String.hashCode() Returns a hash code for this string. The hash code for a String object is computed as s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)
之于相应的解决方法,可以把相应的Filter类抓出来,如ProtocolCodecFitler:
public class MyProtocolCodecFilter extends IoFilterAdapter { /** A logger for this class */ private static final Logger LOGGER = LoggerFactory.getLogger(MyProtocolCodecFilter.class); private static final Class<?>[] EMPTY_PARAMS = new Class[0]; private static final IoBuffer EMPTY_BUFFER = IoBuffer.wrap(new byte[0]); private final AttributeKey ENCODER = new AttributeKey(MyProtocolCodecFilter.class, "encoder"); private final AttributeKey DECODER = new AttributeKey(MyProtocolCodecFilter.class, "decoder"); private final AttributeKey DECODER_OUT = new AttributeKey(MyProtocolCodecFilter.class, "decoderOut"); private final AttributeKey ENCODER_OUT = new AttributeKey(MyProtocolCodecFilter.class, "encoderOut"); ... ... }
connector.getFilterChain().addLast("my-codec", new ProtocolCodecFilter(new OwspMessageFactory()));
connector.getFilterChain().addLast("my-codec", new MyProtocolCodecFilter(new OwspMessageFactory()));
Mina中关于多个同类型Filter(如ProtocolCodecFilter)实例共存问题的解决,布布扣,bubuko.com
Mina中关于多个同类型Filter(如ProtocolCodecFilter)实例共存问题的解决
原文地址:http://blog.csdn.net/oathevil/article/details/37601391