Java学习笔记-第十五章-通用API

一、日志

1. 日志API简介

public static void main(String[] args) throws IOException {
        Logger logger = Logger.getLogger(Main.class.getName());
        logger.setLevel(Level.FINE);
        for (Handler handler : logger.getParent().getHandlers()) {
            handler.setLevel(Level.FINE);
        }
        //日志信息要经过Logger和Handler的同时过滤，所以要同时设置Logger和Handler的level才能输出日志
        logger.log(Level.WARNING, "WARNING");
        logger.log(Level.INFO, "INFO");
        logger.log(Level.CONFIG, "CONFIG");
        logger.log(Level.FINE, "FINE");
    }

• 如果客户端调用了logger的log方法，首先会根据Level过滤信息，在看看Logger有无设定Filter接口的实例，如果有且其isLoggable()返回true，才会调用Handler实例的publish()方法，Handler也可以设定自己的Filter实例，如果有且其isLoggable()返回true，就调用Formatter实例的format()方法格式化信息，最后才调用输出对象，将格式化后的信息输出。
• 简单来说，Logger是记录信息的起点，要输出的信息必须先经过Logger的Level与Filter过滤，再通过Handler的Level与Filter过滤，格式化信息的动作交给Formatter，输出信息的动作实际上是Handler负责

2. 指定日志层级

		logger.setLevel(Level.FINE);
        for (Handler handler : logger.getParent().getHandlers()) {
            handler.setLevel(Level.FINE);
        }

3. 使用Handler与Formatter

public static void main(String[] args) throws IOException {
        Logger logger = Logger.getLogger(Main.class.getName());
        logger.setLevel(Level.CONFIG);
        //%h表示用户根目录 C:\Users\username
        //%t表示系统暂存目录 %g表示按照序号递增log文件
        Handler handler = new FileHandler("%h/config%g.log");
        handler.setLevel(Level.CONFIG);
        logger.addHandler(handler);
        logger.log(Level.WARNING, "WARNING");
        logger.log(Level.INFO, "INFO");
        logger.log(Level.CONFIG, "CONFIG");
        logger.log(Level.FINE, "FINE");
    }

• FileHandler默认的Formatter是XMLFormatter，所以输出的文件为xml格式的
  
  
• 可以通过handler的setFormatter()方法设定Formatter
• 如果不想让父Logger的Handler处理日志，可以调用Logger实例的setUseParentHandler()为false
• handler setEncoding()可以设置文字编码

4. 自定义Handler、Formatter、与Filter

package com.leo;

import java.util.logging.Handler;
import java.util.logging.LogRecord;

/** * @ClassName: CustomHandler * @Author: Leo * @Description: * @Date: 8/6/2019 2:55 PM */
public class CustomHandler extends Handler {
    @Override
    public void publish(LogRecord record) {
        if (isLoggable(record)) {
            return;
        }
        String longMsg = getFormatter().format(record);
        //输出到控制台 这里可以自定义目的地
        System.out.println(longMsg);
    }

    @Override
    public void flush() {
        //出清信息
    }

    @Override
    public void close() throws SecurityException {
        //关闭输出对象
    }
}

public static void main(String[] args) throws IOException {
        Logger logger = Logger.getLogger(Main.class.getName());
        logger.setLevel(Level.CONFIG);
        //%h表示用户根目录 C:\Users\username
        //%t表示系统暂存目录 %g表示按照序号递增log文件
        Handler handler = new FileHandler("%h/config%g.log");
        handler.setLevel(Level.CONFIG);
        logger.addHandler(handler);
        logger.log(Level.WARNING, "WARNING");
        logger.log(Level.INFO, "INFO");
        logger.log(Level.CONFIG, "CONFIG");
        logger.log(Level.FINE, "FINE");
        handler.setFormatter(new Formatter() {
            @Override
            public String format(LogRecord record) {
                return "日志来自：" + record.getSourceClassName();
            }
        });
    }

5. 使用logging.properties

• 在jdk的conf文件夹中，有logging.properties示例文档：

############################################################
#  	Default Logging Configuration File
#
# You can use a different file by specifying a filename
# with the java.util.logging.config.file system property.  
# For example java -Djava.util.logging.config.file=myfile
############################################################

############################################################
#  	Global properties
############################################################

# "handlers" specifies a comma separated list of log Handler 
# classes.  These handlers will be installed during VM startup.
# Note that these classes must be on the system classpath.
# By default we only configure a ConsoleHandler, which will only
# show messages at the INFO and above levels.
handlers= java.util.logging.ConsoleHandler

# To also add the FileHandler, use the following line instead.
#handlers= java.util.logging.FileHandler, java.util.logging.ConsoleHandler

# Default global logging level.
# This specifies which kinds of events are logged across
# all loggers.  For any given facility this global level
# can be overriden by a facility specific level
# Note that the ConsoleHandler also has a separate level
# setting to limit messages printed to the console.
.level= INFO

############################################################
# Handler specific properties.
# Describes specific configuration info for Handlers.
############################################################

# default file output is in user's home directory.
java.util.logging.FileHandler.pattern = %h/java%u.log
java.util.logging.FileHandler.limit = 50000
java.util.logging.FileHandler.count = 1
# Default number of locks FileHandler can obtain synchronously.
# This specifies maximum number of attempts to obtain lock file by FileHandler
# implemented by incrementing the unique field %u as per FileHandler API documentation.
java.util.logging.FileHandler.maxLocks = 100
java.util.logging.FileHandler.formatter = java.util.logging.XMLFormatter

# Limit the message that are printed on the console to INFO and above.
java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter

# Example to customize the SimpleFormatter output format 
# to print one-line log message like this:
#     <level>: <log message> [<date/time>]
#
# java.util.logging.SimpleFormatter.format=%4$s: %5$s [%1$tc]%n

############################################################
# Facility specific properties.
# Provides extra control for each logger.
############################################################

# For example, set the com.xyz.foo logger to only log SEVERE
# messages:
# com.xyz.foo.level = SEVERE

• 修改此配置文件，然后放到项目的classpath中，通常为resources文件夹，然后在启动jvm的时候添加参数：
• -Djava.util.logging.config.file=logging.properties

二、国际化

internationalization 简称i18n（因为i到n之间有18个字母）

地区（Locale）
资源包（Resource bundle）
基础名称（Base Name）

三、正则表达式

API:https://docs.oracle.com/en/java/javase/12/docs/api/java.base/java/util/regex/Pattern.html

1. 字面意义字符

2. 字符类

四、处理数字

BigInteger、BigDecimal