java的各种日志框架

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java日志框架有很多,这篇文章我们来整理一下各大主流的日志框架,

包括log4j   logback  jul(java.util.logging)  jcl(commons-logging)  slf4j(simple log facade for java)等常用框架

目前java日志的使用有两种形式:日志接口和日志实现

1.目前日志接口，常用的有两种，jcl(commons logging)和slf4j(simple log facade for java)。

2.日志实现目前有这几类，log4j、jul、logback、log4j2。

我们先从log4j开始

首先,引入maven依赖

　　　
    <dependency>
      <groupId>log4jgroupId>
      <artifactId>log4jartifactId>
      <version>1.2.17version>
    dependency>

然后是配置log4j.properties文件

### 设置###
log4j.rootLogger = debug,stdout,D,E

### 输出信息到控制抬 ###
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

### 输出DEBUG 级别以上的日志到=E://logs/error.log ###
log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = E://logs/log.log
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG 
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

### 输出ERROR 级别以上的日志到=E://logs/error.log ###
log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =E://logs/error.log 
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR 
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

最后是代码

import org.apache.log4j.Logger;

public class Log4j {

    public static void main(String[] args) {

        Logger log4j = Logger.getLogger("log4j");
        // 记录debug级别的信息
        log4j.debug("This is debug message.");
        // 记录info级别的信息
        log4j.info("This is info message.");
        // 记录error级别的信息
        log4j.error("This is error message.");
    }

}

最后是日志信息

 

 

 好,到这里,log4j就差不多了

 

,接下来我们看下 jul(java.util.logging) java官方日志jul，位于java.util.logging包下,不用引入依赖,但功能有限,不太常用看下demo

import java.util.logging.Logger;

public class JUL {

    public static void main(String[] args) {
        //获取logger实例，相同名的只能生成一个实例
        Logger logger = Logger.getLogger("javaLog");
        //日志输出简写形式，有不同的级别
        logger.warning("warning log");
        logger.info("info log");

    }

}

看下控制台输出结果,可以看出和log4j相比,日志的时间和颜色明显不同

 

 

  好,到这里,jul就差不多了

 

我们再看jcl(commons logging)是如何整合log4j和jul的

首先还是加入maven依赖,这里我们先加入log4j的依赖

　　
    
      log4j
      log4j
      1.2.17
    

    
    
      commons-logging
      commons-logging
      1.2
    

看下demo

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Created by admin on 2019/10/14.
 */
public class JCL {

    public static void main(String[] args) {
        Log log = LogFactory.getLog("JCL");
        log.error("Hello World");
    }

}

看下输出结果

 

 

 我们看到,这个好像是log4j的实现,我们把log4j的依赖注释,重新运行一次,再看下结果

 

 

 我们发现这次用的好像是jul打印的日志了,下面我们看下源码,看下jcl的底层是如何实现这种切换的

这里也只贴关键代码,看下getInstance方法

public Log getInstance(String name) throws LogConfigurationException {
        Log instance = (Log) instances.get(name);
        if (instance == null) {
            instance = newInstance(name);
            instances.put(name, instance);
        }
        return instance;
    }

继续看newInstance方法

protected Log newInstance(String name) throws LogConfigurationException {
        Log instance;
        try {
            if (logConstructor == null) {
                instance = discoverLogImplementation(name);//我们看这行代码
            }
            else {
                Object params[] = { name };
                instance = (Log) logConstructor.newInstance(params);
            }

            if (logMethod != null) {
                Object params[] = { this };
                logMethod.invoke(instance, params);
            }

            return instance;

        } catch (LogConfigurationException lce) {

            // this type of exception means there was a problem in discovery
            // and we've already output diagnostics about the issue, etc.;
            // just pass it on
            throw lce;

        } catch (InvocationTargetException e) {
            // A problem occurred invoking the Constructor or Method
            // previously discovered
            Throwable c = e.getTargetException();
            throw new LogConfigurationException(c == null ? e : c);
        } catch (Throwable t) {
            handleThrowable(t); // may re-throw t
            // A problem occurred invoking the Constructor or Method
            // previously discovered
            throw new LogConfigurationException(t);
        }
    }

看下上面我注释的代码

private Log discoverLogImplementation(String logCategory)
        throws LogConfigurationException {
        if (isDiagnosticsEnabled()) {
            logDiagnostic("Discovering a Log implementation...");
        }

        initConfiguration();

        Log result = null;

        // See if the user specified the Log implementation to use
        String specifiedLogClassName = findUserSpecifiedLogClassName();

        if (specifiedLogClassName != null) {
            if (isDiagnosticsEnabled()) {
                logDiagnostic("Attempting to load user-specified log class '" +
                    specifiedLogClassName + "'...");
            }

            result = createLogFromClass(specifiedLogClassName,
                                        logCategory,
                                        true);
            if (result == null) {
                StringBuffer messageBuffer =  new StringBuffer("User-specified log class '");
                messageBuffer.append(specifiedLogClassName);
                messageBuffer.append("' cannot be found or is not useable.");

                // Mistyping or misspelling names is a common fault.
                // Construct a good error message, if we can
                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LOG4J_LOGGER);
                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_JDK14_LOGGER);
                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LUMBERJACK_LOGGER);
                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_SIMPLE_LOGGER);
                throw new LogConfigurationException(messageBuffer.toString());
            }

            return result;
        }

        if (isDiagnosticsEnabled()) {
            logDiagnostic(
                "No user-specified Log implementation; performing discovery" +
                " using the standard supported logging implementations...");
        }
        for(int i=0; inull; ++i) {//这里就是关键代码
            result = createLogFromClass(classesToDiscover[i], logCategory, true);
        }

        if (result == null) {
            throw new LogConfigurationException
                        ("No suitable Log implementation");
        }

        return result;
    }

看下我注释的地方,classesToDiscover对象

private static final String[] classesToDiscover = {
            LOGGING_IMPL_LOG4J_LOGGER,
            "org.apache.commons.logging.impl.Jdk14Logger",
            "org.apache.commons.logging.impl.Jdk13LumberjackLogger",
            "org.apache.commons.logging.impl.SimpleLog"
    }

这里的Jdk14Logger其实就是jul,我们发现classesToDiscover对象是一个数组,它包含了几个日志框架的的全限定路径

回到刚刚的代码,我看可以看到,jcl就是遍历这个数组,按顺序取值,这里有log4j,就优先log4j,没有的话,就是要jul框架

我们再看下下面一行代码,点进去,看看怎么实现的

private Log createLogFromClass(String logAdapterClassName,
                                   String logCategory,
                                   boolean affectState)
        throws LogConfigurationException {

        if (isDiagnosticsEnabled()) {
            logDiagnostic("Attempting to instantiate '" + logAdapterClassName + "'");
        }

        Object[] params = { logCategory };
        Log logAdapter = null;
        Constructor constructor = null;

        Class logAdapterClass = null;
        ClassLoader currentCL = getBaseClassLoader();

        for(;;) {
            // Loop through the classloader hierarchy trying to find
            // a viable classloader.
            logDiagnostic("Trying to load '" + logAdapterClassName + "' from classloader " + objectId(currentCL));
            try {
                if (isDiagnosticsEnabled()) {
                    // Show the location of the first occurrence of the .class file
                    // in the classpath. This is the location that ClassLoader.loadClass
                    // will load the class from -- unless the classloader is doing
                    // something weird.
                    URL url;
                    String resourceName = logAdapterClassName.replace('.', '/') + ".class";
                    if (currentCL != null) {
                        url = currentCL.getResource(resourceName );
                    } else {
                        url = ClassLoader.getSystemResource(resourceName + ".class");
                    }

                    if (url == null) {
                        logDiagnostic("Class '" + logAdapterClassName + "' [" + resourceName + "] cannot be found.");
                    } else {
                        logDiagnostic("Class '" + logAdapterClassName + "' was found at '" + url + "'");
                    }
                }

                Class c;
                try {
                    c = Class.forName(logAdapterClassName, true, currentCL);
                } catch (ClassNotFoundException originalClassNotFoundException) {
                    // The current classloader was unable to find the log adapter
                    // in this or any ancestor classloader. There's no point in
                    // trying higher up in the hierarchy in this case..
                    String msg = originalClassNotFoundException.getMessage();
                    logDiagnostic("The log adapter '" + logAdapterClassName + "' is not available via classloader " +
                                  objectId(currentCL) + ": " + msg.trim());
                    try {
                        // Try the class classloader.
                        // This may work in cases where the TCCL
                        // does not contain the code executed or JCL.
                        // This behaviour indicates that the application
                        // classloading strategy is not consistent with the
                        // Java 1.2 classloading guidelines but JCL can
                        // and so should handle this case.
                        c = Class.forName(logAdapterClassName);//这里通过反射获取日志实现类的class对象
                    } catch (ClassNotFoundException secondaryClassNotFoundException) {
                        // no point continuing: this adapter isn't available
                        msg = secondaryClassNotFoundException.getMessage();
                        logDiagnostic("The log adapter '" + logAdapterClassName +
                                      "' is not available via the LogFactoryImpl class classloader: " + msg.trim());
                        break;
                    }
                }

                constructor = c.getConstructor(logConstructorSignature);
                Object o = constructor.newInstance(params);//这里实例化了日志实现类对象 

　　　　　　　　if (o instanceof Log) {//这里判断是否是log的实现类
                logAdapterClass = c;
                logAdapter = (Log) o;//这里将对象传给logAdapter
                break;
            }

            // Oops, we have a potential problem here. An adapter class
            // has been found and its underlying lib is present too, but
            // there are multiple Log interface classes available making it
            // impossible to cast to the type the caller wanted. We
            // certainly can't use this logger, but we need to know whether
            // to keep on discovering or terminate now.
            //
            // The handleFlawedHierarchy method will throw
            // LogConfigurationException if it regards this problem as
            // fatal, and just return if not.
            handleFlawedHierarchy(currentCL, c);
        } catch (NoClassDefFoundError e) {
            // We were able to load the adapter but it had references to
            // other classes that could not be found. This simply means that
            // the underlying logger library is not present in this or any
            // ancestor classloader. There's no point in trying higher up
            // in the hierarchy in this case..
            String msg = e.getMessage();
            logDiagnostic("The log adapter '" + logAdapterClassName +
                          "' is missing dependencies when loaded via classloader " + objectId(currentCL) +
                          ": " + msg.trim());
            break;
        } catch (ExceptionInInitializerError e) {
            // A static initializer block or the initializer code associated
            // with a static variable on the log adapter class has thrown
            // an exception.
            //
            // We treat this as meaning the adapter's underlying logging
            // library could not be found.
            String msg = e.getMessage();
            logDiagnostic("The log adapter '" + logAdapterClassName +
                          "' is unable to initialize itself when loaded via classloader " + objectId(currentCL) +
                          ": " + msg.trim());
            break;
        } catch (LogConfigurationException e) {
            // call to handleFlawedHierarchy above must have thrown
            // a LogConfigurationException, so just throw it on
            throw e;
        } catch (Throwable t) {
            handleThrowable(t); // may re-throw t
            // handleFlawedDiscovery will determine whether this is a fatal
            // problem or not. If it is fatal, then a LogConfigurationException
            // will be thrown.
            handleFlawedDiscovery(logAdapterClassName, currentCL, t);
        }

        if (currentCL == null) {
            break;
        }

        // try the parent classloader
        // currentCL = currentCL.getParent();
        currentCL = getParentClassLoader(currentCL);
    }

    if (logAdapterClass != null && affectState) {
        // We've succeeded, so set instance fields
        this.logClassName   = logAdapterClassName;
        this.logConstructor = constructor;

        // Identify the setLogFactory method (if there is one)
        try {
            this.logMethod = logAdapterClass.getMethod("setLogFactory", logMethodSignature);
            logDiagnostic("Found method setLogFactory(LogFactory) in '" + logAdapterClassName + "'");
        } catch (Throwable t) {
            handleThrowable(t); // may re-throw t
            this.logMethod = null;
            logDiagnostic("[INFO] '" + logAdapterClassName + "' from classloader " + objectId(currentCL) +
                          " does not declare optional method " + "setLogFactory(LogFactory)");
        }

        logDiagnostic("Log adapter '" + logAdapterClassName + "' from classloader " +
                      objectId(logAdapterClass.getClassLoader()) + " has been selected for use.");
    }

    return logAdapter;//返回此对象
}

我们可以看到底层是用了反射获取的对象,截个图

 

 我们可以看到,这里是jcl包里的log4j.

好了,到这里jcl就差不多了,我们从源码可以看出jcl是如何切换日志框架的,

 

接下来学习下目前流行的slf4j,它支持所有主流的日志实现框架,非常强大,推荐使用

老规矩,添加依赖

    
      org.slf4j
      slf4j-api
      1.7.25
    

看下demo

import org.slf4j.LoggerFactory;
import org.slf4j.Logger;


/**
 * Created by admin on 2019/10/14.
 */
public class Slf4j {

    public static void main(String[] args) {
        Logger logger= LoggerFactory.getLogger("slf4j");
        logger.error("Hello World");
    }

}

看下控制台

 

 哎,好像没打印,这里可以看出,只引入slf4j是不打印日志的,我们可以看下官网http://www.slf4j.org/

Simple Logging Facade for Java (SLF4J) 它是简单日志门面,不自己实现

好,我们再引入log4j的绑定器依赖

    
      org.slf4j
      slf4j-log4j12
      1.7.25
    

,再运行一次,看下结果

 

 成了,如何我们要切换日志呢,注释掉log4j,试试jul吧

    

    
    
      org.slf4j
      slf4j-jdk14
      1.7.25
    

再看下控制台

 

 成功了,这就是推荐使用slf4j的原因,切换日志框架非常方便

注意,绑定器有且只能有一个

 

最后,看下logback的使用吧

添加依赖

    
      ch.qos.logback
      logback-core
      1.1.11
    
    
      ch.qos.logback
      logback-classic
      1.1.11
    

logback,xml

    
    logbackStudy

    
    

    
    class="ch.qos.logback.core.ConsoleAppender">
        
            %date %level %logger : %msg %n
        
    

    
    class="ch.qos.logback.core.FileAppender">
        logbackstudy_${nowDate}.log

        
        class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            logbackStudy_%d{yyyyMMdd}.log.gz
            
            30
            
            1G
        
        
            
            %date %level %logger : %msg %n
        
    

    
    
        
        
    

    
        
        
    

demo实例

import org.slf4j.LoggerFactory;
import org.slf4j.Logger;


/**
 * Created by admin on 2019/10/14.
 */
public class Slf4j {

    public static void main(String[] args) {
        Logger logger= LoggerFactory.getLogger("slf4j");
        logger.error("Hello World");
    }

}

控制台

 

 输出的文件

总结:目前来说日志框架推荐使用slf4j日志接口+一个你熟悉的日志实现,这样可以直接切换日志的依赖,不用改已有的代码