How to implement custom log formatters for log messages in Go?

In Go, you can implement custom log formatters for log messages by creating a new type that implements the log.Formatter interface. The log.Formatter interface defines a single method called Format, which takes a log entry and returns a formatted string.

Here's an example of how you can implement a custom log formatter:

package main

import (
	"fmt"
	"log"
	"os"
)

type CustomFormatter struct{}

func (f *CustomFormatter) Format(entry *log.Entry) ([]byte, error) {
	return []byte(fmt.Sprintf("[%s] %s\n", entry.Level, entry.Message)), nil
}

func main() {
	logger := log.New(os.Stdout, "", 0)
	logger.SetFormatter(&CustomFormatter{})
	logger.Println("Hello, world!")
}

In this example, we define a CustomFormatter struct that implements the Format method of the log.Formatter interface. The Format method takes a log entry, which contains the log level and log message, and returns a formatted string.

In the main function, we create a new log.Logger instance and set its formatter to an instance of our CustomFormatter struct. Then, we can use the logger to log messages as usual.

The CustomFormatter in this example simply formats the log entry as "[log-level] log-message". You can customize the output format as per your needs by modifying the Format method.