主题
- 本篇是Slf4j 源码解析的第二篇，上篇介绍了无日志实现框架的执行流程
- 本篇解析添加 slf4j-simple 日志实现框架的脉络
- 已经知道：org/sfl4j/impl/StaticLoggerBinder.class 是连接日志实现框架和Slf4j facade 的桥梁
先浏览下slf4j-simple.jar的目录结构
- 关键是探求如何与Slf4j-api.jar facade 关联的，实现框架项目的复杂简单 not care
//如下是 slf4j-simple.jar 项目的结构示意图
//最主要的就是 org.slf4j.impl 包路径
slf4j-simple
src
main
java //sources
org.slf4j.impl //package
SimpleLogger.java
SimpleLoggerFactory.java
StaticLoggerBinder.java
SimpleLoggerConfiguration.java
......
resources
......
......
pom.xml
pom.xml
4.0.0
org.slf4j
slf4j-parent
1.7.25
slf4j-simple
jar
SLF4J Simple Binding
SLF4J Simple binding
http://www.slf4j.org
org.slf4j
slf4j-api
org.slf4j
slf4j-api
test-jar
${project.version}
test
详细流程
- step1：入口
public class LogDemo {
public static void main(String[] args) {
Logger logger = LoggerFactory.getLogger(LogDemo.class); //断点处
logger.info("log");
System.out.println("log test");
}
}
- Step2：中间跳过与上一篇文章相同之处，进入寻找 StaticLoggerBinder.class方法
// We need to use the name of the StaticLoggerBinder class, but we can't
// reference
// the class itself.
private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class";
static Set findPossibleStaticLoggerBinderPathSet() {
// use Set instead of list in order to deal with bug #138
// LinkedHashSet appropriate here because it preserves insertion order
// during iteration
Set staticLoggerBinderPathSet = new LinkedHashSet();
try {
ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
Enumeration paths;
if (loggerFactoryClassLoader == null) {
paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
} else {
//此处是关键能找到 StaticLoggerFactory.class 文件
//file:/D:/local/mvnrepo/org/slf4j/slf4j-simple/1.7.25/slf4j-simple-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class
//paths.size() == 1
paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
}
while (paths.hasMoreElements()) {
URL path = paths.nextElement();
staticLoggerBinderPathSet.add(path);
}
} catch (IOException ioe) {
Util.report("Error getting resources from path", ioe);
}
//携带者StaticLoogerBinder.class URL 返回
return staticLoggerBinderPathSet;
}
- Step3：进入bind()
private final static void bind() {
try {
Set staticLoggerBinderPathSet = null;
// skip check under android, see also
// http://jira.qos.ch/browse/SLF4J-328
if (!isAndroid()) {
//Step2 中已经找到，向下执行
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
// the next line does the binding
//因为Step2 中明确已经找到 StaticLoggerBinder class,故此时不会抛异常，进入getSingleton()
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
reportActualBinding(staticLoggerBinderPathSet);
fixSubstituteLoggers();
replayEvents();
// release all resources in SUBST_FACTORY
SUBST_FACTORY.clear();
} catch (NoClassDefFoundError ncde) {
String msg = ncde.getMessage();
if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
} else {
failedBinding(ncde);
throw ncde;
}
} catch (java.lang.NoSuchMethodError nsme) {
String msg = nsme.getMessage();
if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) {
INITIALIZATION_STATE = FAILED_INITIALIZATION;
Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
Util.report("Your binding is version 1.5.5 or earlier.");
Util.report("Upgrade your binding to version 1.6.x.");
}
throw nsme;
} catch (Exception e) {
failedBinding(e);
throw new IllegalStateException("Unexpected initialization failure", e);
}
}
- Step4：进入StaticLoggerBinder.getSingleton()
- StaticLoggerBinder 定义于slf4j-simple.jar 中
package org.slf4j.impl; //slf4j-api.jar 中定义的static StaticLoggerBinder.class 包路径
import org.slf4j.ILoggerFactory; //slf4j-api的包
import org.slf4j.spi.LoggerFactoryBinder; //slf4j-api的包
public class StaticLoggerBinder implements LoggerFactoryBinder {
//这里用了饿汉单例模式生成 StaticLoggerBinder 类的实例
private static final StaticLoggerBinder SINGLETON = new StaticLoggerBinder();
public static String REQUESTED_API_VERSION = "1.6.99";
private static final String loggerFactoryClassStr = SimpleLoggerFactory.class.getName();
//每个StaticLoggerBinder 绑定了一个 ILoggerFactory 用以返回具体的 LoggerFactory 此处绑定的是 SimpleLoggerFactory
private final ILoggerFactory loggerFactory = new SimpleLoggerFactory();
//返回 StaticLoggerBinder 单例
public static final StaticLoggerBinder getSingleton() {
return SINGLETON;
}
private StaticLoggerBinder() {
}
//返回日志工厂
public ILoggerFactory getLoggerFactory() {
return this.loggerFactory;
}
public String getLoggerFactoryClassStr() {
return loggerFactoryClassStr;
}
}
- Step5：返回 bind 方法
private final static void bind() {
try {
Set staticLoggerBinderPathSet = null;
// skip check under android, see also
// http://jira.qos.ch/browse/SLF4J-328
if (!isAndroid()) {
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
// the next line does the binding
//成功执行
StaticLoggerBinder.getSingleton();
// INITIALIZATION_STATE 赋值成功
// bind 结束
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
reportActualBinding(staticLoggerBinderPathSet);
fixSubstituteLoggers();
replayEvents();
// release all resources in SUBST_FACTORY
SUBST_FACTORY.clear();
} catch (NoClassDefFoundError ncde) {
String msg = ncde.getMessage();
if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
} else {
failedBinding(ncde);
throw ncde;
}
} catch (java.lang.NoSuchMethodError nsme) {
String msg = nsme.getMessage();
if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) {
INITIALIZATION_STATE = FAILED_INITIALIZATION;
Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
Util.report("Your binding is version 1.5.5 or earlier.");
Util.report("Upgrade your binding to version 1.6.x.");
}
throw nsme;
} catch (Exception e) {
failedBinding(e);
throw new IllegalStateException("Unexpected initialization failure", e);
}
}
- Step：返回 performInitialization
private final static void performInitialization() {
bind();
if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
versionSanityCheck();
}
}
- Step：返回 getILoggerFactory()
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == UNINITIALIZED) {
synchronized (LoggerFactory.class) {
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITIALIZATION;
//执行结束
performInitialization();
}
}
}
//进入switch
switch (INITIALIZATION_STATE) {
//此时INITIALIZATION_STATE 成功初始化
case SUCCESSFUL_INITIALIZATION:
//拿到LoggerFactory,然后返回
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case NOP_FALLBACK_INITIALIZATION:
return NOP_FALLBACK_FACTORY;
case FAILED_INITIALIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITIALIZATION:
// support re-entrant behavior.
// See also http://jira.qos.ch/browse/SLF4J-97
return SUBST_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
- Step：
public static Logger getLogger(String name) {
//取得LoggerFactory
ILoggerFactory iLoggerFactory = getILoggerFactory();
//通过LoggerFactory 得到具体日志框架
return iLoggerFactory.getLogger(name);
}
- Step：返回main
public static void main(String[] args) {
Logger logger = LoggerFactory.getLogger(LogDemo.class);
logger.info("log");
URL ls = Logger.class.getClassLoader().getResource("org/slf4j/Logger.class");
System.out.println("log test");
}