minLog

最小开销的Java日志

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overview

MinLog: 一个很小的Java日志库:

零开销
低于给定级别的日志记录在编译时被javac自动删除。这意味着应用程序可以有详细的跟踪和调试日志，而不会对最终产品产生任何影响。

极致轻薄
整个项目由一个Java文件和大约100行非注释代码组成。
简单有效 简单的API，高效的运行时。

minlog-slf4j适配slf4j的替代实现.

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Usage:

<groupId>com.esotericsoftware</groupId>
<artifactId>minlog</artifactId>
<version>1.3.2-SNAPSHOT</version>

Usage

Messages are logged using static methods:

Log.info("Some message.");  
Log.debug("Error reading file: " + file, ex);  

A static import can be used to make the logging more concise:

import static com.esotericsoftware.minlog.Log.*;  
// ...  
info("Some message.");  
debug("Error reading file: " + file, ex);  

While optional, for brevity the rest of this documentation assumes this static import is in place.

If log statements from different libraries or areas of an application need to be differentiated, a category can be specified as the first argument:

info("some lib", "Some message.");  
debug("some lib", "Error reading file: " + file, ex);  

Log level

Setting the level will log that level, as well as all higher levels. There are multiple ways to set the current level:

Log.set(LEVEL_INFO);  
Log.INFO();  
INFO();  

The levels are:

• NONE disables all logging.
• ERROR is for critical errors. The application may no longer work correctly.
• WARN is for important warnings. The application will continue to work correctly.
• INFO is for informative messages. Typically used for deployment.
• DEBUG is for debug messages. This level is useful during development.
• TRACE is for trace messages. A lot of information is logged, so this level is usually only needed when debugging a problem.

Conditional logging

If a logging method below the current level is called, it will return without logging the message. In order to avoid string concatenation, the current log level can be checked before the message is logged:

if (ERROR) error("Error reading file: " + file, ex);  
if (TRACE) {  
   StringBuilder builder = new StringBuilder();  
   // Do work, append to the builder.  
   trace(builder);  
}  

Fixed logging levels

MinLog users can choose from the regular “minlog.jar” or from from a JAR file like “minlog-info.jar” which has a fixed logging level that cannot be changed at runtime. When a fixed level JAR is used, code that changes the level will have no affect. During compilation, any conditional logging statements below the fixed level will be automatically removed by the Java compiler. This means they will have absolutely no impact on the application.

Output customization

The default logger outputs messages in this format:

time level: [category] message  

Where “time” is the time elapsed since the application started. For example:

00:00 TRACE: [kryo] Wrote string: moo  
00:00 TRACE: [kryo] Wrote object: NonNullTestClass  
00:01 TRACE: [kryo] Wrote string: this is some data  
00:01 TRACE: [kryo] Compressed to 7.97% using: DeflateCompressor  
00:12 TRACE: [kryo] Decompressed using: DeflateCompressor  
00:12 TRACE: [kryo] Read string: this is some data  

The output can be customized:

static public class MyLogger extends Logger {  
   public void log (int level, String category, String message, Throwable ex) {  
	  StringBuilder builder = new StringBuilder(256);  
	  builder.append(new Date());  
	  builder.append(' ');  
	  builder.append(level);  
	  builder.append('[');  
	  builder.append(category);  
	  builder.append("] ");  
	  builder.append(message);  
	  if (ex != null) {  
		 StringWriter writer = new StringWriter(256);  
		 ex.printStackTrace(new PrintWriter(writer));  
		 builder.append('\n');  
		 builder.append(writer.toString().trim());  
	  }  
	  System.out.println(builder);  
   }  
}    // ...  
Log.setLogger(new MyLogger());  

Using this mechanism, log messages can be filtered (eg, by category), written to a file, etc.