How to package jar application using Golang

background

Want to package one of your SpringBoot applications into executable files. See how Golang does it.

Go's go:embed function introduction and packaging JAR file examples

go:embedis a powerful feature introduced in Go 1.16, which allows external files or directories to be embedded into Go programs at compile time. Here is how to use itgo:embedto embed the JAR file.

1. go:embed Basic introduction

Basic Features

• Embed file contents at compile time
• Supports embedding of single files, multiple files, or entire directories
• Three embedding types are supported:
  • string- Used for text files
  • []byte- For binary files
  • - Used for file system (supports multiple files/directories)

Basic syntax

import "embed"
//go:embed 
var fileContent string
//go:embed 
var imageData []byte
//go:embed templates/*
var templatesFS 

2. Embed JAR file example

Suppose you have one that needs to be embeddedFile, the following is the complete example:

Project structure

project/
├── embedded/
│   └──     # JAR file to be embedded├── 
└── 

Code implementation

package main
import (
	"embed"
	"io"
	"log"
	"os"
	"path/filepath"
)
//go:embed embedded/
var jarFile []byte
func main() {
	// Specify the output path (can be temporary directory or specific location)	outputPath := ((), "")
	// Write embedded JAR to file system	err := (outputPath, jarFile, 0755)
	if err != nil {
		("Failed to write JAR file: %v", err)
	}
	("JAR file extracted to: %s", outputPath)
	// Now you can use this JAR file, for example by running it	// ("java", "-jar", outputPath)
}

3. Advanced usage: Embed multiple files or directories

If you have multiple JAR files that need to be embedded:

//go:embed embedded/*.jar
var jarFiles 
func main() {
	// List all embedded JAR files	entries, err := ("embedded")
	if err != nil {
		(err)
	}
	// Extract all JAR files	for _, entry := range entries {
		if (()) == ".jar" {
			data, err := ("embedded/" + ())
			if err != nil {
				("Failed to read %s: %v", (), err)
				continue
			}
			outputPath := ((), ())
			err = (outputPath, data, 0755)
			if err != nil {
				("Failed to write %s: %v", (), err)
				continue
			}
			("Extracted %s to %s", (), outputPath)
		}
	}
}

4. Precautions for use

Path rules：

• go:embedThe path is relative to the Go source file containing the instruction
• Cannot include.or..Equal path components
• Cannot match files in parent directory

File size limit：

• Go 1.16+ has no hard limit on embedded file size
• But very large files may increase compile time and binary size

Build constraints：

• The embedded file must be available at build time
• If the file does not exist, the build will fail

Safety considerations：

• Pay attention to the permissions of the target path when extracting embedded files
• Consider using a temporary directory and clean it up when the program exits

5. Practical application scenarios

• Packaging Java applications: Embed the dependency JAR file into the Go program and then passCall Java to run
• Embedded database: Such as SQLite database file
• Web server resources: HTML/CSS/JS and other front-end resources
• Configuration File: Default configuration template

6. Complete example: Running an embedded JAR

package main
import (
	"embed"
	"log"
	"os"
	"os/exec"
	"path/filepath"
)
//go:embed 
var jarFile []byte
func main() {
	// Create temporary files	tmpFile, err := ("", "embedded-*.jar")
	if err != nil {
		(err)
	}
	defer (()) // Delete when the program exits	// Write JAR content	if _, err := (jarFile); err != nil {
		(err)
	}
	if err := (); err != nil {
		(err)
	}
	// Execute Java commands	cmd := ("java", "-jar", ())
	 = 
	 = 
	("Starting Java application...")
	if err := (); err != nil {
		("Java application failed: %v", err)
	}
}

This way you can package your Java application into a Go binary and then distribute and start it through a Go program.

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