Class org.apache.logging.slf4j.Log4jLogger does not implement the requested interface org.slf4j.Logg

项目中遇到了一个异常：

java.lang.IncompatibleClassChangeError: Class org.apache.logging.slf4j.Log4jLogger does not implement the requested interface org.slf4j.Logger

看了下Log4jLogger的声明：

public class Log4jLogger implements LocationAwareLogger, Serializable {
public interface LocationAwareLogger extends Logger {

package org.slf4j;
public interface Logger {

org.apache.logging.slf4j.Log4jLogger明明是org.slf4j.Logger的子类？这个问题一般是由于类加载器不一样导致的。的确，项目中用到了URLClassLoader加载使用其他jar。

解决办法，org.slf4j.Logger这个类全部使用application classloader加载，即在loadClass方法中过滤掉org.slf4j.Logger，不用URLClassLoader加载该类。

@Override
protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
    Class cl;
    if (name.equals("org.slf4j.Logger")) {
        cl = this.getClass().getClassLoader().loadClass(name);
    } else {
        try {
            cl = super.loadClass(name, resolve);
        } catch (ClassNotFoundException ex) {
            cl = this.getClass().getClassLoader().loadClass(name);
        }
    }
    return cl;
}