Play with Java in Node.js

Over the years, JavaScript has gone from being “the world’s most misunderstood language” to “the world’s most popular language” thanks to the rise of Node.js. And the pace of development, in terms of the evolution of the language itself, the growth of libraries and packages, the improvement of tool support, the emergence of STAR projects and domain solutions, the expansion of platforms, technology stacks, application domains, etc., is unprecedented. With the popularity of Node.js services, a question arises for companies whose back-end services are Java: how does Node.js communicate with Java?

What’s on today?

Instead of architectural design and traditional HTTP, socket, and RPC communication protocols, let’s talk about how to connect to Java apis in Node.js applications — in other words, write Java code directly in Node.js.

node-java

To connect node.js to Java, you need a Node-Java module.

Environment to prepare

Operating system: Supports OSX and Linux

Operating environment (recommended) :

Install the module

The minimum Nodejs LTS version must be 6.x
Java JDK 1.8 +
Linux GCC 4.8.1 +

$ npm install java

If Liunx does not support c++ 11, you need to manually upgrade GCC to GCC 4.8

If you need to install the old Java SE 6 runtime environment, please download JDK 2015

Call the Java Node. Js

HelloWorld

java


      
       public class HelloWorld {
         public static void main(String[] args) {
             System.out.println("Hello World!");
         }
       }
      
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Output: Hello World!

Node.js


      
       const java = require('java')
       const javaLangSystem = java.import('java.lang.System')
       
       javaLangSystem.out.printlnSync('Hello World! ')
      
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Output: Hello World!

Operating a Java Map

Java HashMap operation


      
       import java.util.HashMap;
       import java.util.Map;
       
       public class HashMapDemo {
         public static void main(String[] args) {
           Map<String. Object> map = new HashMap< > ();
       
           map.put("name". "SunilWang");
           map.put("age". 20);
       
           String name = (String) map.get("name");
           int age = (int) map.get("age");
       
           System.out.printf(Name: "" % s". name);
           System.out.println("");
           System.out.printf("Age: % d". age);
         }
       }
      
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Output: name: SunilWang age: 20

Node.js calls the Java HashMap synchronously


      
       const java = require('java')
       const HashMap = java.import('java.util.HashMap')
       // Synchronize the operation
       
       let hashMap = new HashMap(a)
       
       hashMap.putSync('name'. 'SunilWang')
       hashMap.putSync('age'. 20)
       
       let name = hashMap.getSync('name')
       let age = hashMap.getSync('age')
       
       console.log('name'. name)
       console.log('age'. age)
      
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Output: name: SunilWang age: 20

Node.js callback calls the Java HashMap


      
       const java = require('java')
       const HashMap = java.import('java.util.HashMap')
       / / callback operation
       
       let hashMap = new HashMap(a)
       
       hashMap.put('name'. 'SunilWang'. (error. info) = > {
         if (error) console.log('put name Error: '. error)
         hashMap.get('name'. (error. name) = > {
           if (error) console.log('get name Error: '. error)
           console.log('% s' callback name.. name)
         })
       })
      
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Output: callback name: SunilWang

Node.js Promise calls the Java HashMap


      
       const co = require('co')
       const java = require('java')
       
       // The current configuration must be declared at the top
       java.asyncOptions = {
         syncSuffix: 'Sync'. // Synchronization method name suffix
         asyncSuffix: ' '. // Asynchronous method name suffix
         promiseSuffix: 'Promise'. // Promise method name suffix
         promisify: require('bluebird').promisify // The module that depends on Promise
       }
       
       / / = = = = = = = = = = = = = =
       
       const HashMap = java.import('java.util.HashMap')
       
       / / Promise
       co(function * (a) {
         let hashMap = new HashMap(a)
       
         yield hashMap.putPromise('name'. 'SunilWang')
         yield hashMap.putPromise('age'. '20')
       
         let name = yield hashMap.getPromise('name')
         let age = yield hashMap.getPromise('age')
       
         console.log('name'. name)
         console.log('age'. age)
       })
      
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There are two ways to create a Java instance

Java


      
       import java.util.ArrayList;
       import java.util.List;
       
       public class ArrayListDemo {
       
         public static void main(String[] args) {
           List<String> list1 = new ArrayList< > ();
           List<String> list2 = new ArrayList< > ();
       
           list1.add("item1");
           list2.add("item1");
       
           System.out.printf("size: %d". list1.size()); / / 2
           System.out.println("");
           // list1 equals list2: true
           System.out.printf("list1 equals list2: %s". list1.equals(list2)); 
         }
       }
      
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newInstanceSync


      
       const java = require('java')
       
       let list1 = java.newInstanceSync('java.util.ArrayList')
       
       console.log(list1.sizeSync()) / / 0
       list1.addSync('item1')
       console.log(list1.sizeSync()) / / 1
      
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import & new


      
       let ArrayList = java.import('java.util.ArrayList')
       let list2 = new ArrayList(a)
       
       list2.addSync('item1')
       
       let equalValue = list2.equalsSync(list1) 
       console.log(equalValue)// true
      
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Other operating

Fast new data group

Java


      
       public class CharArrayDemo {
       
         public static void main(String[] args) {
           char [] charArray = "hello world\n".toCharArray(a);
           // charArray length: 12
           System.out.printf("charArray length: %d". charArray.length);
         }
       }
      
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Node.js


      
       let charArray = java.newArray('char'. 'hello world\n'.split(' '))
       // [ 'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '\n' ]
       console.log(charArray.length) / / 12
      
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Fast New Long object

Java


      
       public class LongDemo {
       
         public static void main(String[] args) {
           Long num = new Long("5");
           System.out.println(num);
           System.out.println(num.longValue());
         }
       }
      
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Node.js


      
       let javaLong = java.newInstanceSync('java.lang.Long'. 5)
       // Possibly truncated long value: 5
       console.log('Possibly truncated long value: %d'. javaLong)
       // Original long value (as a string): 5
       console.log('Original long value (as a string): %s'. javaLong.longValue)
      
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Node.js calls its own compiled classes

Java


      
       package com.nearinfinity.nodeJava;
       
       public class MyClass {
         public static int addNumbers(int a. int b) {
           return a + b;
         }
       }
      
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Node.js


      
       const java = require('java')
       java.classpath.push('./src')
       
       let MyClass = java.import('com.nearinfinity.nodeJava.MyClass')
       
       let result = MyClass.addNumbersSync(1. 2)
       console.log(result)
       
       let javaInteger = java.newInstanceSync('java.lang.Integer'. 2)
       
       // Quickly call a method in a Java static class
       result = java.callStaticMethodSync('com.nearinfinity.nodeJava.MyClass'. 'addNumbers'. javaInteger. 3)
       console.log(result)
      
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conclusion

This is just the tip of the node-Java iceberg. The Node-Java API is rich, such as the JVM, instantiating a class, calling class static methods, quickly instantiating an object, and so on.

The quickest way to learn is to look at the documentation: Node-java.

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