Java Nashorn

Java Nashorn is a JavaScript engine that is integrated into the Java Development Kit (JDK) since Java 8. It provides an environment to execute JavaScript code within a Java Virtual Machine (JVM) and provides interoperability between Java and JavaScript. Nashorn is an acronym for “not another stupid heap of redundant nonsense,” and it was developed by Oracle as an alternative to the Rhino JavaScript engine that was included in previous versions of Java.

Nashorn provides support for the ECMAScript 5.1 standard and some features from ECMAScript 6 (ES6). It also provides a command-line tool for running JavaScript code and a Java API for embedding Nashorn into Java applications. Nashorn allows Java developers to use JavaScript code in their Java applications, making it easier to use JavaScript libraries and frameworks in Java.

One of the advantages of Nashorn is that it provides better performance than Rhino, which was the previous JavaScript engine in Java. Nashorn is designed to leverage the JVM’s optimizations, making it faster and more efficient. Nashorn also provides a “jjs” command-line tool that allows developers to run JavaScript code interactively, similar to how they would use the “javac” command-line tool to compile Java code.

Overall, Nashorn provides a convenient way for Java developers to work with JavaScript code and take advantage of the benefits of both languages in their applications. However, as of JDK 15, Nashorn has been deprecated and is no longer supported. Developers are encouraged to use other JavaScript engines such as Graal.js or Rhino if they need to execute JavaScript within the JVM.

Example: Executing by Using Terminal:

Sure, here’s an example of how to execute JavaScript code using Nashorn from the terminal/command line:

1. Open a terminal/command prompt window.
2. Navigate to the directory where your JavaScript file is located.
3. Type the following command to launch the Nashorn shell:

jjs

4. Once the Nashorn shell has launched, type the following command to load your JavaScript file:

load("yourfilename.js")

This will execute the code in your JavaScript file.

For example, if your JavaScript file is named “mycode.js”, you would type:

load("mycode.js")

5. You should see the output of your JavaScript code in the terminal/command prompt window.

For example, if your JavaScript code outputs the text “Hello, World!”, you would see:

Hello, World!

That’s it! This is a simple example of how to execute JavaScript code using Nashorn from the terminal/command line.

Example: Executing JavaScript file in Java Code:

Sure, here’s an example of how to execute a JavaScript file in Java code using Nashorn:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.io.FileReader;
import java.io.IOException;

public class NashornExample {
    public static void main(String[] args) throws ScriptException, IOException {
        // Create a Nashorn script engine
        ScriptEngineManager engineManager = new ScriptEngineManager();
        ScriptEngine engine = engineManager.getEngineByName("nashorn");

        // Load the JavaScript file
        FileReader fileReader = new FileReader("mycode.js");

        try {
            // Evaluate the JavaScript code
            engine.eval(fileReader);
        } finally {
            // Close the file reader
            fileReader.close();
        }
    }
}

In this example, we first create a ScriptEngine object by using the ScriptEngineManager class. We then load the JavaScript file by creating a FileReader object and passing it the filename of the JavaScript file. Finally, we call the eval() method of the ScriptEngine object to execute the JavaScript code.

Note that in this example, we assume that the mycode.js file is located in the same directory as the Java source code file. If the file is located in a different directory, you would need to specify the full path to the file. Additionally, you may need to handle exceptions that may be thrown by the ScriptEngine or FileReader classes.

Overall, this example demonstrates how to execute a JavaScript file within a Java application using Nashorn.

Example: Embedding JavaScript Code in Java Source File:

Sure, here’s an example of how to embed JavaScript code within a Java source file using Nashorn:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class NashornExample {
    public static void main(String[] args) throws ScriptException {
        // Create a Nashorn script engine
        ScriptEngineManager engineManager = new ScriptEngineManager();
        ScriptEngine engine = engineManager.getEngineByName("nashorn");

        // Define the JavaScript code to execute
        String jsCode = "var a = 5; var b = 10; print('The sum of ' + a + ' and ' + b + ' is ' + (a + b));";

        // Evaluate the JavaScript code
        engine.eval(jsCode);
    }
}

In this example, we first create a ScriptEngine object by using the ScriptEngineManager class, just like in the previous example. However, instead of loading a JavaScript file using a FileReader object, we define the JavaScript code as a String variable named jsCode.

We then pass the jsCode variable to the eval() method of the ScriptEngine object to execute the JavaScript code.

Note that in this example, we use the print() function to output the result of the JavaScript code to the console. This function is a Nashorn-specific function that is not part of standard JavaScript. If you want to output the result using standard JavaScript, you can use the console.log() function instead.

Overall, this example demonstrates how to embed JavaScript code within a Java source file and execute it using Nashorn.

Example: Embedding JavaScript Expression:

Sure, here’s an example of how to embed a JavaScript expression within a Java source file using Nashorn:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class NashornExample {
    public static void main(String[] args) throws ScriptException {
        // Create a Nashorn script engine
        ScriptEngineManager engineManager = new ScriptEngineManager();
        ScriptEngine engine = engineManager.getEngineByName("nashorn");

        // Define the JavaScript expression to evaluate
        String jsExpression = "2 * (3 + 4)";

        // Evaluate the JavaScript expression
        Object result = engine.eval(jsExpression);

        // Print the result
        System.out.println(result);
    }
}

In this example, we first create a ScriptEngine object by using the ScriptEngineManager class, just like in the previous examples. We then define the JavaScript expression to evaluate as a String variable named jsExpression. The expression in this case is 2 * (3 + 4).

We then pass the jsExpression variable to the eval() method of the ScriptEngine object to evaluate the expression. The result of the expression is returned as an Object that we store in the result variable.

Finally, we print the result variable to the console using the System.out.println() method.

Overall, this example demonstrates how to embed a JavaScript expression within a Java source file and evaluate it using Nashorn.

Heredocs:

In Java, there is no direct equivalent of heredocs like in some other programming languages. However, there are a few workarounds that can be used to achieve a similar effect.

One way to achieve a similar effect is by using multi-line string literals. In Java, a multi-line string literal is created by enclosing the string in triple quotes (“””). Here is an example:

String text = """
    This is a multi-line string.
    It can span multiple lines
    without the need for escape characters.
    """;

In this example, the text variable contains a multi-line string that spans three lines. Note that the triple quotes must be on a line by themselves both at the beginning and at the end of the string.

Another way to achieve a similar effect is by using a StringBuilder to concatenate multiple strings. Here is an example:

StringBuilder sb = new StringBuilder();
sb.append("This is a multi-line string.\n");
sb.append("It can span multiple lines\n");
sb.append("without the need for escape characters.\n");
String text = sb.toString();

In this example, we use a StringBuilder to append multiple strings together to form a multi-line string. Note that we use the \n character to represent a new line.

Overall, while there is no direct equivalent of heredocs in Java, these workarounds can be used to achieve a similar effect.

Example : Heredocs in JavaScript File

Heredocs are not natively supported in JavaScript either, but we can use Template Literals (also known as Template Strings) to achieve a similar effect. Here’s an example:

const text = 
    This is a multi-line string.
    It can span multiple lines
    without the need for escape characters.
;

console.log(text);

In this example, we define a multi-line string using the backtick character () instead of the usual single or double quotes. This is known as a Template Literal or a Template String. We can then use the string variable textas needed, such as outputting it to the console usingconsole.log(). Note that Template Literals also support the use of expressions within the string using the <code>${}</code> syntax. For example: <pre class="EnlighterJSRAW" data-enlighter-language="generic">const firstName = "John"; const lastName = "Doe"; const fullName =
My name is ${firstName} ${lastName}.
Nice to meet you!
`;

console.log(fullName);

In this example, we define a multi-line string using a Template Literal, but also include expressions within the string using ${}. These expressions are evaluated and their values are included in the resulting string.

Example: Setting JavaScript variable in Java File

Sure, here’s an example of how to set a JavaScript variable from a Java file using Nashorn:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class NashornExample {
    public static void main(String[] args) throws ScriptException {
        // Create a Nashorn script engine
        ScriptEngineManager engineManager = new ScriptEngineManager();
        ScriptEngine engine = engineManager.getEngineByName("nashorn");

        // Set a JavaScript variable
        engine.eval("var x = 10;");

        // Get the value of the JavaScript variable
        Object result = engine.eval("x");

        // Print the value of the JavaScript variable
        System.out.println(result);
    }
}

In this example, we first create a ScriptEngine object by using the ScriptEngineManager class, just like in the previous examples. We then use the eval() method of the ScriptEngine object to set a JavaScript variable named x to the value 10.

We can then use the eval() method again to get the value of the x variable and store it in the result variable. Finally, we print the value of the result variable to the console, which in this case is the value of the x variable that we set earlier.

Overall, this example demonstrates how to set a JavaScript variable from a Java file using Nashorn.

Import Java Package in JavaScript File:

In Nashorn, you can import a Java package in a JavaScript file using the JavaImporter function. Here’s an example:

var ArrayList = Java.type('java.util.ArrayList');
var list = new ArrayList();

list.add('apple');
list.add('banana');
list.add('orange');

print(list);

In this example, we use the Java.type() function to import the java.util.ArrayList class from the Java Standard Library. We can then create a new ArrayList object and add some elements to it. Finally, we use the print() function to output the contents of the ArrayList to the console.

Note that when you import a Java package using Java.type(), you need to use the fully qualified name of the class, including the package name. If you’re importing a class from your own Java code, you’ll need to use the package name and class name that you defined in your Java code.

Also, you can use JavaImporter to import multiple classes from the same package in a more concise way. Here’s an example:

var imports = new JavaImporter(java.util, java.io);

with (imports) {
    var list = new ArrayList();
    list.add('apple');
    list.add('banana');
    list.add('orange');

    var writer = new FileWriter('output.txt');
    writer.write(list.toString());
    writer.close();
}

In this example, we create a new JavaImporter object that imports the java.util and java.io packages. We then use a with statement to create a scope in which the imported classes are available without having to specify the package name. Inside the scope, we can create an ArrayList object and a FileWriter object and use them as needed. Finally, we write the contents of the ArrayList to a file using the write() method of the FileWriter object.

Example1: Import Java Package in JavaScript File

Sure, here’s an example of how to import a Java package and use a class from it in a JavaScript file using Nashorn:

var SimpleDateFormat = Java.type('java.text.SimpleDateFormat');
var Date = Java.type('java.util.Date');

var sdf = new SimpleDateFormat('dd/MM/yyyy HH:mm:ss');
var now = new Date();

print('Current date and time: ' + sdf.format(now));

In this example, we use the Java.type() function to import the java.text.SimpleDateFormat and java.util.Date classes from the Java Standard Library. We then create a new SimpleDateFormat object with a format string and a new Date object to represent the current date and time. Finally, we use the format() method of the SimpleDateFormat object to format the date and time as a string, and output it to the console using the print() function.

Note that in this example, we use the Java.type() function to import each class separately, but you can also use JavaImporter to import multiple classes from the same package in a more concise way, as I explained in the previous answer.

Example2: Import Java Package in JavaScript File

It is not possible to import a Java package directly into a JavaScript file because Java and JavaScript are two different programming languages that run on different platforms. Java runs on the Java Virtual Machine (JVM), while JavaScript runs on a web browser or Node.js environment.

However, if you want to use Java code in a JavaScript application, you can use a tool like GraalVM, which allows you to run Java code in a JavaScript environment. GraalVM provides a JavaScript engine that can execute JavaScript code as well as a Java Virtual Machine that can execute Java code.

To use GraalVM, you need to first install it on your system and then create a JavaScript file that can interact with the Java code. You can do this by using the GraalVM polyglot API, which allows you to write code in multiple languages within the same application.

Here is an example of how you can use GraalVM to call a Java method from a JavaScript file:

First, create a Java class with a method that you want to call from JavaScript:

package com.example;

public class MyJavaClass {
    public static String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}

Then, create a JavaScript file that can call the sayHello method:

const { polyglot } = require('graalvm');

const javaClass = polyglot.eval('js', 'Java.type("com.example.MyJavaClass")');

const result = javaClass.sayHello('John');

console.log(result); // Output: "Hello, John!"

In this example, the polyglot object is used to evaluate a JavaScript expression that creates a reference to the MyJavaClass class. Then, the sayHello method is called with the javaClass.sayHello syntax, passing in a name parameter. Finally, the result is logged to the console.

Example3: Import Java Package in JavaScript File

Unfortunately, it is not possible to directly import a Java package in a JavaScript file. Java and JavaScript are two different programming languages that run on different platforms. Java runs on the Java Virtual Machine (JVM), while JavaScript runs on a web browser or Node.js environment.

However, if you want to use Java code in a JavaScript application, you can use a tool like Node-java, which provides a bridge between Node.js and Java.

To use Node-java, you need to first install it on your system and then create a JavaScript file that can interact with the Java code. Here is an example of how to use Node-java to call a Java method from a JavaScript file:

First, create a Java class with a method that you want to call from JavaScript:

package com.example;

public class MyJavaClass {
    public static String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}

Then, create a JavaScript file that can call the sayHello method using Node-java:

const java = require('java');

java.classpath.push('path/to/my/java/class');

const MyJavaClass = java.import('com.example.MyJavaClass');

const result = MyJavaClass.sayHello('John');

console.log(result); // Output: "Hello, John!"

import javax.script.*;

public class Main {
    public static void main(String[] args) throws Exception {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        engine.eval("function sayHello(name) { print('Hello, ' + name + '!'); }");
        Invocable invocable = (Invocable) engine;
        invocable.invokeFunction("sayHello", "John");
    }
}

public class Main {
    public static void main(String[] args) {
        String name = "John";
        String greeting = sayHello(name);
        System.out.println(greeting);
    }

    public static String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}