FAQ about logging mechanism in Java functions?

Answers to common logging questions in Java functions: Register a logger: Use Logger.getLogger(class name) to register. Set the log level: set through logger.setLevel(Level), for example, Level.FINE means outputting FINE level and above information. Use placeholders and parameters: Use new Object[] {parameter 1, parameter 2} placeholders and parameters to pass information. Contains exception information: Use logger.log(Level.SEVERE, "Exception message", e) to log exception information. Output to file: Create a FileHandler and add it to the logger, and set the file handler level.

FAQ about logging mechanism in Java functions

Question 1: How to register a logger?

Code:

import java.util.logging.Logger;

public class LoggingExample {

    private static final Logger logger = Logger.getLogger(LoggingExample.class.getName());

    public static void main(String[] args) {
        // 注册日志记录器
        logger.info("日志消息");
    }
}

Question 2: How to set the log level?

Code:

import java.util.logging.Level;
import java.util.logging.Logger;

public class LoggingExample {

    private static final Logger logger = Logger.getLogger(LoggingExample.class.getName());

    public static void main(String[] args) {
        // 设置日志级别为 FINE
        logger.setLevel(Level.FINE);

        // 输出 FINE 级别及以上的消息
        logger.info("日志消息");
        logger.fine("详细日志消息");
    }
}

Question 3: How to use placeholders and parameters to pass information?

Code:

import java.util.logging.Logger;

public class LoggingExample {

    private static final Logger logger = Logger.getLogger(LoggingExample.class.getName());

    public static void main(String[] args) {
        // 使用占位符和参数传递信息
        logger.info("订单 {0} 已被创建，金额为 {1}", new Object[] {12345, 100.0});
    }
}

Question 4: How to include exception information in log messages?

Code:

import java.util.logging.Level;
import java.util.logging.Logger;

public class LoggingExample {

    private static final Logger logger = Logger.getLogger(LoggingExample.class.getName());

    public static void main(String[] args) {
        try {
            // 发生异常
            throw new Exception("异常发生");
        } catch (Exception e) {
            // 记录异常信息
            logger.log(Level.SEVERE, "异常发生", e);
        }
    }
}

Question 5: How to output the log to a file?

Code:

1. Create Log File Processor

import java.io.File;
import java.util.logging.FileHandler;
import java.util.logging.Level;
import java.util.logging.Logger;

public class LoggingExample {

    private static final Logger logger = Logger.getLogger(LoggingExample.class.getName());

    public static void main(String[] args) throws Exception {
        // 创建日志文件处理器
        FileHandler fileHandler = new FileHandler("my.log");

        // 将日志文件处理器添加到日志记录器
        logger.addHandler(fileHandler);
    }
}

2. Set file processor level

// 设置文件处理器的日志级别
fileHandler.setLevel(Level.INFO);

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