Passing byte arrays between Java and JavaScript: A comprehensive guide

Question

Passing byte arrays between Java and JavaScript: A comprehensive guide

My current objective involves accessing a SecureRandom Java Object from Javascript. I aim to extract 4 bytes from the PRNG and convert it into a Javascript integer variable. The documentation states that the following two lines of Java code can be used to obtain 4 random bytes:

byte bytes[] = new byte[4];
random.nextBytes(bytes);

The main hurdles I'm facing are: 1) Allocating a byte array suitable for passing to a Java method 2) Parsing that array into an integer afterwards

Currently, I have managed to use the getSeed() method which returns an array of random bytes. When I view the rendered HTML code in Firefox, it displays "[B@16f70a4", which seems to be some form of pointer.

<script>
var sprng = new java.security.SecureRandom();
random = sprng.getSeed(4);
document.write(random + "<br/>\n");
</script>

This situation leads me to believe that I have successfully instantiated and accessed the Java class but encounter difficulties with type conversion.

I am seeking assistance in creating functions allocateJavaByteArray(N) and convertJavaByteArrayToInt(N) to enable the following code to function smoothly:

var sprng = new java.security.SecureRandom();
var nextBytes = allocateJavaByteArray(4);
srng.nextBytes(nextBytes);
var nextInt = convertJavaByteArrayToInt(4);

Your help is greatly appreciated.

java javascript arrays byte

Answer 1

Answer №1

If you want to create a function called convertJavaByteArrayToInt, you can do it like this:

function convertJavaByteArrayToInt(bytes) {
  var result = 0;
  for (var index = 0; index < bytes.length; index++) {
    result += (bytes[index] & 0xff) << (8 * index);
  }
  return result;
}

As for implementing allocateJavaByteArray, it can be challenging due to the inability to retrieve the Class of byte. This means using java.lang.reflect.Array.newInstance to create a byte[] instance is not possible. However, here's a clever workaround:

function allocateJavaByteArray(size) {
  var result = "";
  for (var i = 0; i < size; i++) {
    result += "0";
  }
  return new java.lang.String(result).getBytes();
}

Update: The previous code may not work in FireFox 3.6. Here is an alternative implementation of allocateJavaByteArray that you can try:

function allocateJavaByteArray(length) {
  var outStream = new java.io.ByteArrayOutputStream(4);
  for (var i = 0; i < length; i++) {
    outStream.write(0);
  }
  return outStream.toByteArray();
}

Answer 2

If you want to create a function called convertJavaByteArrayToInt, you can do it like this:

function convertJavaByteArrayToInt(bytes) {
  var result = 0;
  for (var index = 0; index < bytes.length; index++) {
    result += (bytes[index] & 0xff) << (8 * index);
  }
  return result;
}

As for implementing allocateJavaByteArray, it can be challenging due to the inability to retrieve the Class of byte. This means using java.lang.reflect.Array.newInstance to create a byte[] instance is not possible. However, here's a clever workaround:

function allocateJavaByteArray(size) {
  var result = "";
  for (var i = 0; i < size; i++) {
    result += "0";
  }
  return new java.lang.String(result).getBytes();
}

Update: The previous code may not work in FireFox 3.6. Here is an alternative implementation of allocateJavaByteArray that you can try:

function allocateJavaByteArray(length) {
  var outStream = new java.io.ByteArrayOutputStream(4);
  for (var i = 0; i < length; i++) {
    outStream.write(0);
  }
  return outStream.toByteArray();
}

Answer 3

Answer №2

Traditionally, the random number is created on the server side and then sent to the jsp via a Request.

Answer 4

Traditionally, the random number is created on the server side and then sent to the jsp via a Request.

Answer 5

Answer №3

One way to start is by creating a random integer upfront using the following method:

let randomNumber = Math.floor(Math.random() * 100);

Answer 6

One way to start is by creating a random integer upfront using the following method:

let randomNumber = Math.floor(Math.random() * 100);

Answer 7

Answer №4

Utilizing Java strings can simplify the process of passing data between Java and JavaScript seamlessly.

When dealing with byte arrays in JavaScript, they will appear as JSObjects.

var sprng = new java.security.SecureRandom();

can be replaced with

var foo= new java.package.SomeClass();

which functions properly in Netscape/Mozilla/FF browsers.

In order for this to work, access to classes is required, either through standard Java classes or by loading a jar file containing the necessary class.

As for the initial question:

Create an applet with a utility method:

public String someStringEncodedValue(){ return 1+"|"+2; }
Include the applet on the page with a unique id
Use JavaScript to locate the applet using the unique id
Invoke the method
Parse the string (split by |)

Answer 8

Utilizing Java strings can simplify the process of passing data between Java and JavaScript seamlessly.

When dealing with byte arrays in JavaScript, they will appear as JSObjects.

var sprng = new java.security.SecureRandom();

can be replaced with

var foo= new java.package.SomeClass();

which functions properly in Netscape/Mozilla/FF browsers.

In order for this to work, access to classes is required, either through standard Java classes or by loading a jar file containing the necessary class.

As for the initial question:

Create an applet with a utility method:

public String someStringEncodedValue(){ return 1+"|"+2; }
Include the applet on the page with a unique id
Use JavaScript to locate the applet using the unique id
Invoke the method
Parse the string (split by |)

Passing byte arrays between Java and JavaScript: A comprehensive guide

Answer №1

Answer №2

Answer №3

Answer №4

Similar questions

Unable to retrieve the child value using getJSON

Challenges arise when integrating PHP variables into JSON

Sending data from PHP to a text file upon clicking a button

Searching for data within a nested array in Mongoose: Tips and techniques

What is the process for uploading an image and entering text into the same row in Google Sheets?

"Discover the method to access values within an associative array or object in an Ember template by utilizing a

Dealing with PhantomJS: Tackling the Challenge of XMLHttpRequest Exception 101 Error

Struggling with Debowerify in Grunt

Attempting to send numerous identifiers in an API request

Tips and tricks for retaining the collapsed state upon reloading Bootstrap 5

AngularJS - varying actions based on which input field I interacted with first

I'm currently in the process of developing a game tool that utilizes classes and functions. One challenge I'm grappling with is how to effectively store game information within an array index. Can

While attempting to run the project I downloaded from GitHub using the command npm run serve, I encountered the following error: "Syntax Error: Error: No ESLint configuration found in

The navigation menu in Javascript is flickering

Retrieving JSON information from a PHP file and saving it as a global variable

Does the arrangement of props matter in JSX?

Error: The variable lecturerFac has not been declared

Can the .setDataArray function handle date types as input?

modify the b-form-checkbox component in a Vue application

Delete the click event listener that was previously assigned by a different script