How to compile nodejs project into jar

Node.js is a very popular JavaScript runtime environment. Large web frameworks such as Vue.js and React Native run on Node.js. However, for Java programmers, compiling Node.js projects into Jar packages may be more convenient for integration into Java projects. In this article, we will introduce how to compile a Node.js project into an executable Jar package.

1. Installing Node.js

First, make sure you have installed Node.js and npm (the Node.js package manager). You can download the appropriate version from the official website (https://nodejs.org).

2. Initialize the project

   mkdir node2jar
   cd node2jar
   npm init

You need to provide information about the project when executing the above command. Some default values ​​may need to be configured by you.

3. Installing dependencies

Next, we need to install dependencies, such as node-jre (which can compile Node.js scripts into Java bytecode) and express.js (Express.js is a popular web application framework). Execute the following command to install dependencies:

npm install --save node-jre
npm install --save express

4. Write Node.js script

In this step, we will write a simple Node.js script, which will output " Hello World" to the terminal. Let’s create a file called index.js and enter the following code:

var express = require('express');
var app = express();
app.get('/', function (req, res) {
  res.send('Hello World!');
});
var server = app.listen(3000, function () {
  console.log('Example app listening at http://localhost:3000');
});

5. Compile Node.js Script to Java Bytecode

Once we have After writing the Node.js script, we can use node-jre to compile it into Java bytecode. Execute the following command:

./node_modules/node-jre/bin/node-jre jre-1.8 index.js

The above command will generate a file named server.jar. Execute the following command to start the server:

java -jar server.jar

At this time, visit http://localhost:3000 and you will see the "Hello World!" output.

6. Dig deeper Secrets

We can use the Exec Maven plug-in to package JRE and Node.js scripts into Jar packages.

Create a file named assembly.xml in the newly created project directory and enter the following content in it:

<assembly>
  <id>jar-with-scripts</id>
  <formats>
    <format>jar</format>
  </formats>
  <includeBaseDirectory>false</includeBaseDirectory>
  <fileSets>
    <fileSet>
      <directory>${project.basedir}</directory>
      <outputDirectory>/</outputDirectory>
      <includes>
        <include>server.jar</include>
        <include>jre-1.8/**</include>
      </includes>
    </fileSet>
  </fileSets>
  <dependencySets/>
</assembly>

Because our application depends on JRE , so we need to package the JRE together into a Jar package, so we include the jre-1.8 directory in the fileset.

Next, add the following content to the <build> tag of the pom.xml file:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-assembly-plugin</artifactId>
      <version>3.3.0</version>
      <configuration>
        <descriptor>assembly.xml</descriptor>
      </configuration>
      <executions>
        <execution>
          <id>make-assembly</id>
          <phase>package</phase>
          <goals>
            <goal>single</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

After that, execute the following command. It can be packaged into a Jar package:

mvn clean package

After the packaging is completed, the target Jar package can be found in the target directory.

Conclusion

In this article, we introduced the method of packaging Node.js projects into Jar packages. We learned how to compile a Node.js script into Java bytecode and package it into a convenient Jar package. Now, we can easily start the Node.js server through Java's java -jar command and integrate it with Java projects.

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