最近在做的项目需要用到memcached，java客户端就选了国产的xmemcached。有个很奇怪的问题，序列化自定义对象是没问题，反序列化对象时就抛出ClassNotFoundException，重新检查这个类，确实存在。

没办法，向google求救，原来，把xmemcached这个包放在tomcat/lib下就会抛出ClassNotFoundException，而放在webapps/[app]/WEB-INF/lib下就正常。估计是不同类加载器的问题。

既然找到了原因，就容易了，打开xmemcached源代码，找到这个类BaseSerializingTranscoder的deserialize方法，用的是jdk提供的ObjectInputStream，又查了jdk文档，只覆盖ObjectInputStream的resolveClass就可以从别的类加载器加载类了。

附上修改后的源代码：

public class CustomerSerializingTranscoder extends SerializingTranscoder {
	public CustomerSerializingTranscoder() {
	}

	@Override
	protected Object deserialize(byte[] in)
	{
		Object rv = null;
		ByteArrayInputStream bis = null;
		ObjectInputStream is = null;
		try {
			if (in != null) {
				bis = new ByteArrayInputStream(in);
				is = new ObjectInputStream(bis) {
							@Override
							protected Class<?> resolveClass(ObjectStreamClass desc)
									throws IOException, ClassNotFoundException {
								try {
						            return Thread.currentThread().getContextClassLoader().loadClass(desc.getName());
						        } catch (ClassNotFoundException e) {
						            return super.resolveClass(desc);
						        }
							}
						};
				rv = is.readObject();
			}
		} catch (IOException e) {
			log.error("Caught IOException decoding " + in.length + " bytes of data", e);
		} catch (ClassNotFoundException e) {
			log.error("Caught CNFE decoding " + in.length + " bytes of data", e);
		} finally {
			if (is != null) {
				try {
					is.close();
				} catch (IOException e) {
				}
			}
			if (bis != null) {
				try {
					bis.close();
				} catch (IOException e) {
				}
			}
		}
		return rv;
	}
}

 然后在spring配置文件里指定这个自定义解码器就行了：

<bean id="memcachedClientBuilder" class="net.rubyeye.xmemcached.XMemcachedClientBuilder">
	...
	<property name="transcoder">
		<bean class="xxx.CustomerSerializingTranscoder" />
	</property>
</bean>

 这样，不管xmemcached是放在tomcat/lib目录下还是webapps/[app]/WEB-INF/lib目录，都不会抛出ClassNotFoundException了