mina read方法出现BufferUnderflowException异常的解决办法

现象：

先连续发几十个很小很小的包(<10 byte)

再忽然发一个大小64byte的包

这时你会发现mina就会出现如下错误
java.nio.BufferUnderflowException
 at java.nio.HeapByteBuffer.get(Unknown Source)
 at org.apache.mina.core.buffer.AbstractIoBuffer.get(AbstractIoBuffer.java:419)
 at org.apache.mina.core.buffer.AbstractIoBuffer.get(AbstractIoBuffer.java:827)
 at com.labox.common.net.ProtocolHandler.messageReceived(ProtocolHandler.java:81)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain$TailFilter.messageReceived(DefaultIoFilterChain.java:752)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain.callNextMessageReceived(DefaultIoFilterChain.java:414)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain.access$5(DefaultIoFilterChain.java:411)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain$EntryImpl$1.messageReceived(DefaultIoFilterChain.java:832)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain$HeadFilter.messageReceived(DefaultIoFilterChain.java:616)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain.callNextMessageReceived(DefaultIoFilterChain.java:414)
 at org.apache.mina.core.filterchain.DefaultIoFilterChain.fireMessageReceived(DefaultIoFilterChain.java:408)
 at org.apache.mina.core.polling.AbstractPollingIoProcessor.read(AbstractPollingIoProcessor.java:582)
 at org.apache.mina.core.polling.AbstractPollingIoProcessor.process(AbstractPollingIoProcessor.java:542)
 at org.apache.mina.core.polling.AbstractPollingIoProcessor.process(AbstractPollingIoProcessor.java:534)
 at org.apache.mina.core.polling.AbstractPollingIoProcessor.access$7(AbstractPollingIoProcessor.java:532)
 at org.apache.mina.core.polling.AbstractPollingIoProcessor$Worker.run(AbstractPollingIoProcessor.java:861)

通过对mina的分析，这是由对包长度不对作成的(即，咱们发的包长是大于64byte的，但他的byteBuffer大小只有64byte，当咱们尝试读取第65个byte就会出现这个错误)

mina怎会出现这种错误的呢？？是否是有什么配置能够调整

找到mina读取byte的方法AbstractPollingIoProcessor类的read(T session)

此方法源代码以下

private void read(T session) {
        IoSessionConfig config = session.getConfig();

        System.out.println("cap buffer size"+config.getReadBufferSize());//这句我本身加的
        IoBuffer buf = IoBuffer.allocate(config.getReadBufferSize());

        final boolean hasFragmentation =
            session.getTransportMetadata().hasFragmentation();

        try {
            int readBytes = 0;
            int ret;

            try {
                if (hasFragmentation) {
                    while ((ret = read(session, buf)) > 0) {
                        readBytes += ret;
                        if (!buf.hasRemaining()) {
                            break;
                        }
                    }
                } else {
                    ret = read(session, buf);
                    if (ret > 0) {
                        readBytes = ret;
                    }
                }
            } finally {
                buf.flip();
            }

            if (readBytes > 0) {
                session.getFilterChain().fireMessageReceived(buf);
                buf = null;

                if (hasFragmentation) {
                    if (readBytes << 1 < config.getReadBufferSize()) {
                        session.decreaseReadBufferSize();
                    } else if (readBytes == config.getReadBufferSize()) {
                        session.increaseReadBufferSize();
                    }
                }
            }
            if (ret < 0) {
                scheduleRemove(session);
            }
        } catch (Throwable e) {
            if (e instanceof IOException) {
                scheduleRemove(session);
            }
            session.getFilterChain().fireExceptionCaught(e);
        }
    }

 

通过对这段代码的分析终于发现问题所在了

你们注意if (readBytes > 0) 这个块下的代码

你不难发现

if (hasFragmentation) {
                    if (readBytes << 1 < config.getReadBufferSize()) {
                        session.decreaseReadBufferSize();
                    } else if (readBytes == config.getReadBufferSize()) {
                        session.increaseReadBufferSize();
                    }
                }

意思是if hasFragmentation==true

if 当前配置初始化ByteBuffer大小 > 当前读取包的平方 为 true 就把配置中初始化byteBuffer大小减半

else if 当前已读取字节==配置包初始化大小  为true时 把配置中初始化byteBuffer大小加倍 

接下来结合我出错的现象看看

当我接连发几十个小于10byte的包时，这时配置中的初始化ByteBuffer大小就为取小，默认最小为64byte

当我再发一个大于64byte的包,但整个ByteBuffer只有64byte，那就出错了。

接下来咱们来修正这个问题

方法一:不要改变默认初始化byteBuffer大小，要修改mina的源码

找到org.apache.mina.transport.socket.nio.NioSocketSession 这个类的METADATA变量

把 new DefaultTransportMetadata()的第四个参数改为false就ok了

方法二:本身写read()方法中获得byteBuffer实例的方法

从read()方法看出，他获得byteBuffer实例是每次去请求的，若是咱们在这里作一个cache，每次从cache中获得，天然byteBuffer的大小也是固定的，只要按本身业务最大包大小去开就能够了。

每一个线程用一个本身的ByteBuffer实例，这样就不会有同步问题.

找到org.apache.mina.core.polling.AbstractPollingIoProcessor类中的read(T session)方法改为

static ThreadLocal readCache=new ThreadLocal();//这个是放ByteBuffer实例的cache

private void read(T session) {

IoBuffer buf=readCache.get();
if(buf==null){
 buf=IoBuffer.allocate(512);//512为包默认大小
 readCache.set(buf);
}else{
 buf.clear();
}

try {
    int readBytes = 0;
    int ret;

    try {
            ret = read(session, buf);
            if (ret > 0) {
                readBytes = ret;
            }
    } finally {
        buf.flip();
    }

    if (readBytes > 0) {
        session.getFilterChain().fireMessageReceived(buf);
    }
    if (ret < 0) {
        scheduleRemove(session);
    }
} catch (Throwable e) {
    if (e instanceof IOException) {
        scheduleRemove(session);
    }
    session.getFilterChain().fireExceptionCaught(e);
}

}

搞定了

ps:不知这个是否是mina的bug，是否是还有别的方法配置的呢？？？

请教那位兄弟有更好的解决方法.

qq:85529766