剖析项目多个logback配置(上)

来源：http://www.cnblogs.com/guozp/p/5949744.html

以下两个是我在使用slf4j + logback时候日志提示的问题，问题不大，都是WARN，并不真正影响运行，但是结果可能不是你希望的结果。

<1>

SLF4J: Found binding in [jar:file:/servers/storm-0.9.0.1/lib/logback-classic-1.0.6.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/servers/test_index/index.jar!/org/slf4j/impl/StaticLoggerBinder.class]

SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

Class path contains multiple SLF4J bindings.

<2>

Could NOT find resource [logback.groovy]
- Could NOT find resource [logback-test.xml]
- Found resource [logback.xml] at [file:/D:/IdeaCode/gitCode/index_file/index_file_service/target/classes/logback.xml]
- Resource [logback.xml] occurs multiple times on the classpath.
 - Resource [logback.xml] occurs at [file:/D:/IdeaCode/index/service/target/classes/logback.xml]
 - Resource [logback.xml] occurs at [file:/D:/IdeaCode/index/dao/target/classes/logback.xml]

简单介绍下SLF4J：

SLF4J(Simple logging Facade for Java)不是一个真正的日志实现，而是一个抽象层，它允许你在后台使用任意一个日志类库。如果是在编写供内外部都可以使用的API或者通用类库，那么你真不会希望使用你类库的客户端必须使用你选择的日志类库。

SLF4j采用了静态绑定来确定具体日志库。静态绑定就是为每一个具体的日志库写一个包名和类名都相同类： org.slf4j.impl.StaticLoggerBinder，这个类的功能就是调用具体的日志库。这个类会存放在Adaptation layer或者native implementation of slf4j-api的jar包中。SLF4j的使用者只要把具体日志库对应的Adaptation layer或者native implementation of slf4j-api的jar包放入classpath中,SLF4j便会装载(load)对应版本的org.slf4j.impl.StaticLoggerBinder，从而调用具体的日志库。

如果项目中之前使用了Log4j，现在要使用SLF4J + LogBack,如果遇到冲突，先观察以下jar包：

(slf4j-XXX-version.jar)
slf4j-log4j12.jar：slf4j提供 log 接口,其具体实现是根据放入程序的绑定器决定.
slf4j-log4j12.jar就是实现通过slf4j调度使用log4j。

(XXX-over-slf4j.jar)
所谓的桥接器即一个假的日志实现工具。
log4j-over-slf4j.jar：是一个桥接器，本来组件是通过log4j输出日志的，通过该桥接器被转到slf4j,slf4j在根据绑器把日志交给具体的日志实现工具。

如果log4j-over-slf4j.jar 和 slf4j-log4j12.jar共存话，就像两个人互相推卸责任不干活，最终陷入死循环。

可以将对应的jar排除

<exclusions>
                <exclusion>
                    <artifactId>slf4j-api</artifactId>
                    <groupId>org.slf4j</groupId>
                </exclusion>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>log4j-over-slf4j</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>

针对情况<1>，一般是在classpath下出现了多个logback可以静态绑定的日志实现，slf4j会默认选择其中的一种实现来绑定，如若出现其他错误再仔细排查。

针对情况<2>，一般是在classpath下出现了多个logback配置文件，一般是在使用了maven不同的模块中使用了不同的配置，其实可以将所有模块公用一个配置。

正如stackoverflow上所述一样，

As far as I'm concerned, you should never package a logging config file (logback.xml, log4j.properties, or what have you) inside a JAR file. The whole point of even having a logging config file is to make it easy for the end-user to adjust logging levels by editing the file. Burying it in an archive defeats the purpose of that, because to change the logging level your user has to expand the archive, edit the file, and then re-package the archive.

Here's my preferred layout for a deployed application. It's a little bit more work to set up, but IMO is worth the trouble because it gives you the flexibility and ease of configuration that an uberjar doesn't.

my-app/
  bin/
    run-app.sh
  config/
    logback.xml
  lib/
    my-lib.jar
    my-app.jar
Your run-app.sh script would look something like:

BIN=`dirname "$0"`
BASE=$BIN/..
java -cp "$BASE/config:$BASE/lib/*" my-app.main
This has the advantage that, by putting the config directory at the front of the classpath, any logging config file found there should take precedence over anything that might be found in one of the JARs (e.g. included by a third-party library that you have no control over).

你最好不要将配置文件打包到jar包中，因为增加配置文件本质上就是为了方便用户调整一下参数配置，如果将它打包到jar包中，你需要修改指定的文件并从新打包，上线。这样的优势在于你可以方便的修改一些线上的配置，并且实时被加载生效。

在这里logback启动的时候，加载配置文件的顺序：

1. 如果指定了 logback.configurationFile性,将使用这个属性的地址，如启动指定了：  java -Dlogback.configurationFile=/path/to/config.xml

2.如果没有配置上面的属性, 将会在classpath中查找  logback.groovy ,如果没有找到文件,依次查找  logback-test.xml, logback.xml 。

3.如果都没有找到, jdk版本如果是 jdk6+,会调用ServiceLoader 查找 com.qos.logback.classic.spi.Configurator接口的第一个实现类

4.如果上面都没有,将使用ch.qos.logback.classic.BasicConfigurator,在控制台输出日志

我将跟进一些源码，粗略的看下都发生了写什么。

入口：org.slf4j.impl.StaticLoggerBinder

void init() {
        try {
            try {
　　　　　　　　　　//这里开始初始化配置
                (new ContextInitializer(this.defaultLoggerContext)).autoConfig();
            } catch (JoranException var2) {
                Util.report("Failed to auto configure default logger context", var2);
            }

            StatusPrinter.printInCaseOfErrorsOrWarnings(this.defaultLoggerContext);
            this.contextSelectorBinder.init(this.defaultLoggerContext, KEY);
            this.initialized = true;
        } catch (Throwable var3) {
            Util.report("Failed to instantiate [" + LoggerContext.class.getName() + "]", var3);
        }

    }

ch.qos.logback.classic.util.ContextInitializer：

public void autoConfig() throws JoranException {
    StatusListenerConfigHelper.installIfAsked(this.loggerContext);
//加载配置文件，logback.groovy(有加载，无继续)---->logback-test.xml(有加载，无继续)------>logback.xml
    URL url = this.findURLOfDefaultConfigurationFile(true);
    if(url != null) {
　　　　//读取设置配置信息
        this.configureByResource(url);
    } else {
      //找不到配置文件，设置默认
        BasicConfigurator.configure(this.loggerContext);
    }

}
//加载配置文件，logback.groovy(有加载，无继续)---->logback-test.xml(有加载，无继续)------>logback.xml
//getResource()---->statusOnResourceSearch()----->multiplicityWarning()--->打印Resource [logback.xml] occurs multiple times on the classpath
public URL findURLOfDefaultConfigurationFile(boolean updateStatus) {
    ClassLoader myClassLoader = Loader.getClassLoaderOfObject(this);
    URL url = this.findConfigFileURLFromSystemProperties(myClassLoader, updateStatus);
    if(url != null) {
        return url;
    } else {
        url = this.getResource("logback.groovy", myClassLoader, updateStatus);
        if(url != null) {
            return url;
        } else {
            url = this.getResource("logback-test.xml", myClassLoader, updateStatus);
            return url != null?url:this.getResource("logback.xml", myClassLoader, updateStatus);
        }
    }
}

private URL getResource(String filename, ClassLoader myClassLoader, boolean updateStatus) {
    URL url = Loader.getResource(filename, myClassLoader);
    if(updateStatus) {
        this.statusOnResourceSearch(filename, myClassLoader, url);
    }

    return url;
}
private void statusOnResourceSearch(String resourceName, ClassLoader classLoader, URL url) {
    StatusManager sm = this.loggerContext.getStatusManager();
    if(url == null) {
        sm.add(new InfoStatus("Could NOT find resource [" + resourceName + "]", this.loggerContext));
    } else {
        sm.add(new InfoStatus("Found resource [" + resourceName + "] at [" + url.toString() + "]", this.loggerContext));
        this.multiplicityWarning(resourceName, classLoader);
    }

}

private void multiplicityWarning(String resourceName, ClassLoader classLoader) {
    Set urlSet = null;
    StatusManager sm = this.loggerContext.getStatusManager();

    try {
        urlSet = Loader.getResourceOccurenceCount(resourceName, classLoader);
    } catch (IOException var7) {
        sm.add(new ErrorStatus("Failed to get url list for resource [" + resourceName + "]", this.loggerContext, var7));
    }

    if(urlSet != null && urlSet.size() > 1) {
        sm.add(new WarnStatus("Resource [" + resourceName + "] occurs multiple times on the classpath.", this.loggerContext));
        Iterator i$ = urlSet.iterator();

        while(i$.hasNext()) {
            URL url = (URL)i$.next();
            sm.add(new WarnStatus("Resource [" + resourceName + "] occurs at [" + url.toString() + "]", this.loggerContext));
        }
    }

}

但是这个时候，如果有两个配置文件，以哪个文件为主呢？详见下篇

完整源代码代码：

ch.qos.logback.classic.util.ContextInitializer：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package ch.qos.logback.classic.util;

import ch.qos.logback.classic.BasicConfigurator;
import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.gaffer.GafferUtil;
import ch.qos.logback.classic.joran.JoranConfigurator;
import ch.qos.logback.classic.util.EnvUtil;
import ch.qos.logback.classic.util.StatusListenerConfigHelper;
import ch.qos.logback.core.joran.spi.JoranException;
import ch.qos.logback.core.status.ErrorStatus;
import ch.qos.logback.core.status.InfoStatus;
import ch.qos.logback.core.status.StatusManager;
import ch.qos.logback.core.status.WarnStatus;
import ch.qos.logback.core.util.Loader;
import ch.qos.logback.core.util.OptionHelper;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Iterator;
import java.util.Set;

public class ContextInitializer {
    public static final String GROOVY_AUTOCONFIG_FILE = "logback.groovy";
    public static final String AUTOCONFIG_FILE = "logback.xml";
    public static final String TEST_AUTOCONFIG_FILE = "logback-test.xml";
    public static final String CONFIG_FILE_PROPERTY = "logback.configurationFile";
    public static final String STATUS_LISTENER_CLASS = "logback.statusListenerClass";
    public static final String SYSOUT = "SYSOUT";
    final LoggerContext loggerContext;

    public ContextInitializer(LoggerContext loggerContext) {
        this.loggerContext = loggerContext;
    }

    public void configureByResource(URL url) throws JoranException {
        if(url == null) {
            throw new IllegalArgumentException("URL argument cannot be null");
        } else {
            if(url.toString().endsWith("groovy")) {
                if(EnvUtil.isGroovyAvailable()) {
                    GafferUtil.runGafferConfiguratorOn(this.loggerContext, this, url);
                } else {
                    StatusManager configurator = this.loggerContext.getStatusManager();
                    configurator.add(new ErrorStatus("Groovy classes are not available on the class path. ABORTING INITIALIZATION.", this.loggerContext));
                }
            }

            if(url.toString().endsWith("xml")) {
                JoranConfigurator configurator1 = new JoranConfigurator();
                configurator1.setContext(this.loggerContext);
                configurator1.doConfigure(url);
            }

        }
    }

    void joranConfigureByResource(URL url) throws JoranException {
        JoranConfigurator configurator = new JoranConfigurator();
        configurator.setContext(this.loggerContext);
        configurator.doConfigure(url);
    }

    private URL findConfigFileURLFromSystemProperties(ClassLoader classLoader, boolean updateStatus) {
        String logbackConfigFile = OptionHelper.getSystemProperty("logback.configurationFile");
        if(logbackConfigFile != null) {
            URL result = null;

            URL e1;
            try {
                result = new URL(logbackConfigFile);
                URL e = result;
                return e;
            } catch (MalformedURLException var13) {
                result = Loader.getResource(logbackConfigFile, classLoader);
                if(result != null) {
                    URL f1 = result;
                    return f1;
                }

                File f = new File(logbackConfigFile);
                if(!f.exists() || !f.isFile()) {
                    return null;
                }

                try {
                    result = f.toURI().toURL();
                    e1 = result;
                } catch (MalformedURLException var12) {
                    return null;
                }
            } finally {
                if(updateStatus) {
                    this.statusOnResourceSearch(logbackConfigFile, classLoader, result);
                }

            }

            return e1;
        } else {
            return null;
        }
    }

    public URL findURLOfDefaultConfigurationFile(boolean updateStatus) {
        ClassLoader myClassLoader = Loader.getClassLoaderOfObject(this);
        URL url = this.findConfigFileURLFromSystemProperties(myClassLoader, updateStatus);
        if(url != null) {
            return url;
        } else {
            url = this.getResource("logback.groovy", myClassLoader, updateStatus);
            if(url != null) {
                return url;
            } else {
                url = this.getResource("logback-test.xml", myClassLoader, updateStatus);
                return url != null?url:this.getResource("logback.xml", myClassLoader, updateStatus);
            }
        }
    }

    private URL getResource(String filename, ClassLoader myClassLoader, boolean updateStatus) {
        URL url = Loader.getResource(filename, myClassLoader);
        if(updateStatus) {
            this.statusOnResourceSearch(filename, myClassLoader, url);
        }

        return url;
    }

    public void autoConfig() throws JoranException {
        StatusListenerConfigHelper.installIfAsked(this.loggerContext);
        URL url = this.findURLOfDefaultConfigurationFile(true);
        if(url != null) {
            this.configureByResource(url);
        } else {
            BasicConfigurator.configure(this.loggerContext);
        }

    }

    private void multiplicityWarning(String resourceName, ClassLoader classLoader) {
        Set urlSet = null;
        StatusManager sm = this.loggerContext.getStatusManager();

        try {
            urlSet = Loader.getResourceOccurenceCount(resourceName, classLoader);
        } catch (IOException var7) {
            sm.add(new ErrorStatus("Failed to get url list for resource [" + resourceName + "]", this.loggerContext, var7));
        }

        if(urlSet != null && urlSet.size() > 1) {
            sm.add(new WarnStatus("Resource [" + resourceName + "] occurs multiple times on the classpath.", this.loggerContext));
            Iterator i$ = urlSet.iterator();

            while(i$.hasNext()) {
                URL url = (URL)i$.next();
                sm.add(new WarnStatus("Resource [" + resourceName + "] occurs at [" + url.toString() + "]", this.loggerContext));
            }
        }

    }

    private void statusOnResourceSearch(String resourceName, ClassLoader classLoader, URL url) {
        StatusManager sm = this.loggerContext.getStatusManager();
        if(url == null) {
            sm.add(new InfoStatus("Could NOT find resource [" + resourceName + "]", this.loggerContext));
        } else {
            sm.add(new InfoStatus("Found resource [" + resourceName + "] at [" + url.toString() + "]", this.loggerContext));
            this.multiplicityWarning(resourceName, classLoader);
        }

    }
}

ch.qos.logback.core.util.Loader：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package ch.qos.logback.core.util;

import ch.qos.logback.core.Context;
import ch.qos.logback.core.util.OptionHelper;
import java.io.IOException;
import java.net.URL;
import java.security.AccessControlException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;

public class Loader {
    static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";
    private static boolean ignoreTCL = false;
    public static final String IGNORE_TCL_PROPERTY_NAME = "logback.ignoreTCL";
    private static boolean HAS_GET_CLASS_LOADER_PERMISSION = false;

    public Loader() {
    }

    public static Set<URL> getResourceOccurenceCount(String resource, ClassLoader classLoader) throws IOException {
        HashSet urlSet = new HashSet();
        Enumeration urlEnum = classLoader.getResources(resource);

        while(urlEnum.hasMoreElements()) {
            URL url = (URL)urlEnum.nextElement();
            urlSet.add(url);
        }

        return urlSet;
    }

    public static URL getResource(String resource, ClassLoader classLoader) {
        try {
            return classLoader.getResource(resource);
        } catch (Throwable var3) {
            return null;
        }
    }

    public static URL getResourceBySelfClassLoader(String resource) {
        return getResource(resource, getClassLoaderOfClass(Loader.class));
    }

    public static ClassLoader getTCL() {
        return Thread.currentThread().getContextClassLoader();
    }

    public static Class loadClass(String clazz, Context context) throws ClassNotFoundException {
        ClassLoader cl = getClassLoaderOfObject(context);
        return cl.loadClass(clazz);
    }

    public static ClassLoader getClassLoaderOfObject(Object o) {
        if(o == null) {
            throw new NullPointerException("Argument cannot be null");
        } else {
            return getClassLoaderOfClass(o.getClass());
        }
    }

    public static ClassLoader getClassLoaderAsPrivileged(final Class clazz) {
        return !HAS_GET_CLASS_LOADER_PERMISSION?null:(ClassLoader)AccessController.doPrivileged(new PrivilegedAction() {
            public ClassLoader run() {
                return clazz.getClassLoader();
            }
        });
    }

    public static ClassLoader getClassLoaderOfClass(Class clazz) {
        ClassLoader cl = clazz.getClassLoader();
        return cl == null?ClassLoader.getSystemClassLoader():cl;
    }

    public static Class loadClass(String clazz) throws ClassNotFoundException {
        if(ignoreTCL) {
            return Class.forName(clazz);
        } else {
            try {
                return getTCL().loadClass(clazz);
            } catch (Throwable var2) {
                return Class.forName(clazz);
            }
        }
    }

    static {
        String ignoreTCLProp = OptionHelper.getSystemProperty("logback.ignoreTCL", (String)null);
        if(ignoreTCLProp != null) {
            ignoreTCL = OptionHelper.toBoolean(ignoreTCLProp, true);
        }

        HAS_GET_CLASS_LOADER_PERMISSION = ((Boolean)AccessController.doPrivileged(new PrivilegedAction() {
            public Boolean run() {
                try {
                    AccessController.checkPermission(new RuntimePermission("getClassLoader"));
                    return Boolean.valueOf(true);
                } catch (AccessControlException var2) {
                    return Boolean.valueOf(false);
                }
            }
        })).booleanValue();
    }
}

参考：

http://stackoverflow.com/questions/18263139/how-do-i-suppress-a-inherited-projects-logback-xml-file-2-logback-xml-in-a-sing

http://stackoverflow.com/questions/3401051/suppress-all-logback-output-to-console

http://jira.qos.ch/browse/LOGBACK-337