proxool的log4j冲突

一、背景

应用代码的日志框架使用slf4j，绑定log4j2实现。不使用log4j1。

近期对日志依赖调整后，发现如下异常

Caused by: java.lang.NoClassDefFoundError: org/apache/log4j/ConsoleAppender
at org.logicalcobwebs.logging.impl.Log4JCategoryLog.initialize(Log4JCategoryLog.java:134)
at org.logicalcobwebs.logging.impl.Log4JCategoryLog.<init>(Log4JCategoryLog.java:120)
at org.logicalcobwebs.logging.impl.Log4jFactory.getInstance(Log4jFactory.java:134)
at org.logicalcobwebs.logging.impl.LogFactoryImpl.getInstance(LogFactoryImpl.java:247)
at org.logicalcobwebs.logging.LogFactory.getLog(LogFactory.java:380)
at org.logicalcobwebs.proxool.configuration.PropertyConfigurator.<clinit>(PropertyConfigurator.java:79)
... 66 more
Caused by: java.lang.ClassNotFoundException: org.apache.log4j.ConsoleAppender
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 79 more

二、查看proxool-0.8.0源码

package org.logicalcobwebs.logging.impl;

public class LogFactoryImpl extends LogFactory {
    public LogFactoryImpl () {
        super ();
        // 尝试使用log4j
        guessConfig ();
    }

    public Log getInstance (Class clazz) throws LogConfigurationException {
        if (proxyFactory != null) {
            return proxyFactory.getInstance (clazz); // line number: 247，调用时发生异常
        }

        return (getInstance (clazz.getName ()));
    }

    // 判断Classpath是否有log4j相关类，有的使用它作为日志框架
    protected void guessConfig () {
        if (isLog4JAvailable ()) {
            proxyFactory = null;
            try {
                Class proxyClass = loadClass ("org.logicalcobwebs.logging.impl.Log4jFactory");
                if (proxyClass != null) {
                    proxyFactory = (LogFactory) proxyClass.newInstance ();
                }
            } catch (Throwable t) {
            }
        }
    }

    // 判断classpath是否有log4j的类：org.apache.log4j.Category
    protected boolean isLog4JAvailable () {
        try {
            loadClass ("org.apache.log4j.Category");
            loadClass ("org.logicalcobwebs.logging.impl.Log4JCategoryLog");
            return (true);
        } catch (Throwable t) {
            return (false);
        }
    }
}

三、解决方案1

1、移除classpath中含org.apache.log4j.Category的类。如log4j-x.jar，log4j-1.2-x.jar。

2、通过配置指定日志框架为JUL。新增配置文件commons-logging.properties。

org.logicalcobwebs.logging.Log=org.logicalcobwebs.logging.impl.Jdk14Logger

代码逻辑参考：org.logicalcobwebs.logging.impl.LogFactoryImpl#getLogConstructor。

Concrete subclass of LogFactory that implements the following algorithm to dynamically select a logging implementation class to instantiate a wrapper for.

Use a factory configuration attribute named org.logicalcobwebs.logging.Log to identify the requested implementation class.

Use the org.logicalcobwebs.logging.Log system property to identify the requested implementation class.

If Log4J is available, return an instance of org.logicalcobwebs.logging.impl.Log4JCategoryLog.

If JDK 1.4 or later is available, return an instance of org.logicalcobwebs.logging.impl.Jdk14Logger.
Otherwise, return an instance of org.logicalcobwebs.logging.impl.NoOpLog.

四、解决方案2

1）proxool的org.logicalcobwebs.logging包的源码来自JCL包org.apache.commons.logging。

2）proxool在0.9.x，源码里不再绑定JCL，而是通过依赖形式引入。

所以，直接把proxool的版本由0.8.0升级至0.9.1，然后新增proxool-cglib-0.9.1。

<dependency>
    <groupId>proxool</groupId>
    <artifactId>proxool</artifactId>
    <version>0.9.1</version>
</dependency>
<dependency>
    <groupId>proxool-cglib</groupId>
    <artifactId>proxool-cglib</artifactId>
    <version>0.9.1</version>
</dependency>

附、proxool的CHANGE LOG

Jakarta’s Commons Logging is now longer bundled with the source and is now a dependency.
We had forked this component (at their version 1.02) to make it simpler for us to deploy but
there are advantages, particular with respect to configuration, to just using
the component direct from Jakarta.

图示：proxool源码里移除了JCL的类，注意包名不同。

图示：JCL中的类