Asked  7 Months ago    Answers:  5   Viewed   76 times

(This question is similar to many questions I have seen but most are not specific enough for what I am doing)

Background:

The purpose of my program is to make it easy for people who use my program to make custom "plugins" so to speak, then compile and load them into the program for use (vs having an incomplete, slow parser implemented in my program). My program allows users to input code into a predefined class extending a compiled class packaged with my program. They input the code into text panes then my program copies the code into the methods being overridden. It then saves this as a .java file (nearly) ready for the compiler. The program runs javac (java compiler) with the saved .java file as its input.

My question is, how do I get it so that the client can (using my compiled program) save this java file (which extends my InterfaceExample) anywhere on their computer, have my program compile it (without saying "cannot find symbol: InterfaceExample") then load it and call the doSomething() method?

I keep seeing Q&A's using reflection or ClassLoader and one that almost described how to compile it, but none are detailed enough for me/I do not understand them completely.

 Answers

87

Take a look at JavaCompiler

The following is based on the example given in the JavaDocs

This will save a File in the testcompile directory (based on the package name requirements) and the compile the File to a Java class...

package inlinecompiler;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;

public class InlineCompiler {

    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder(64);
        sb.append("package testcompile;n");
        sb.append("public class HelloWorld implements inlinecompiler.InlineCompiler.DoStuff {n");
        sb.append("    public void doStuff() {n");
        sb.append("        System.out.println("Hello world");n");
        sb.append("    }n");
        sb.append("}n");

        File helloWorldJava = new File("testcompile/HelloWorld.java");
        if (helloWorldJava.getParentFile().exists() || helloWorldJava.getParentFile().mkdirs()) {

            try {
                Writer writer = null;
                try {
                    writer = new FileWriter(helloWorldJava);
                    writer.write(sb.toString());
                    writer.flush();
                } finally {
                    try {
                        writer.close();
                    } catch (Exception e) {
                    }
                }

                /** Compilation Requirements *********************************************************************************************/
                DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
                JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
                StandardJavaFileManager fileManager = compiler.getStandardFileManager(diagnostics, null, null);

                // This sets up the class path that the compiler will use.
                // I've added the .jar file that contains the DoStuff interface within in it...
                List<String> optionList = new ArrayList<String>();
                optionList.add("-classpath");
                optionList.add(System.getProperty("java.class.path") + File.pathSeparator + "dist/InlineCompiler.jar");

                Iterable<? extends JavaFileObject> compilationUnit
                        = fileManager.getJavaFileObjectsFromFiles(Arrays.asList(helloWorldJava));
                JavaCompiler.CompilationTask task = compiler.getTask(
                    null, 
                    fileManager, 
                    diagnostics, 
                    optionList, 
                    null, 
                    compilationUnit);
                /********************************************************************************************* Compilation Requirements **/
                if (task.call()) {
                    /** Load and execute *************************************************************************************************/
                    System.out.println("Yipe");
                    // Create a new custom class loader, pointing to the directory that contains the compiled
                    // classes, this should point to the top of the package structure!
                    URLClassLoader classLoader = new URLClassLoader(new URL[]{new File("./").toURI().toURL()});
                    // Load the class from the classloader by name....
                    Class<?> loadedClass = classLoader.loadClass("testcompile.HelloWorld");
                    // Create a new instance...
                    Object obj = loadedClass.newInstance();
                    // Santity check
                    if (obj instanceof DoStuff) {
                        // Cast to the DoStuff interface
                        DoStuff stuffToDo = (DoStuff)obj;
                        // Run it baby
                        stuffToDo.doStuff();
                    }
                    /************************************************************************************************* Load and execute **/
                } else {
                    for (Diagnostic<? extends JavaFileObject> diagnostic : diagnostics.getDiagnostics()) {
                        System.out.format("Error on line %d in %s%n",
                                diagnostic.getLineNumber(),
                                diagnostic.getSource().toUri());
                    }
                }
                fileManager.close();
            } catch (IOException | ClassNotFoundException | InstantiationException | IllegalAccessException exp) {
                exp.printStackTrace();
            }
        }
    }

    public static interface DoStuff {

        public void doStuff();
    }

}

Now updated to include suppling a classpath for the compiler and loading and execution of the compiled class!

Tuesday, June 1, 2021
 
godot
answered 7 Months ago
43

How do I load a Java Class that is not compiled?

You need to compile it first. This can be done programmatically with the javax.tools API. This only requires the JDK being installed at the local machine on top of JRE.

Here's a basic kickoff example (leaving obvious exception handling aside):

// Prepare source somehow.
String source = "package test; public class Test { static { System.out.println("hello"); } public Test() { System.out.println("world"); } }";

// Save source in .java file.
File root = new File("/java"); // On Windows running on C:, this is C:java.
File sourceFile = new File(root, "test/Test.java");
sourceFile.getParentFile().mkdirs();
Files.write(sourceFile.toPath(), source.getBytes(StandardCharsets.UTF_8));

// Compile source file.
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
compiler.run(null, null, null, sourceFile.getPath());

// Load and instantiate compiled class.
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { root.toURI().toURL() });
Class<?> cls = Class.forName("test.Test", true, classLoader); // Should print "hello".
Object instance = cls.newInstance(); // Should print "world".
System.out.println(instance); // Should print "test.Test@hashcode".

Which yields like

hello
world
test.Test@ab853b

Further use would be more easy if those classes implements a certain interface which is already in the classpath.

SomeInterface instance = (SomeInterface) cls.newInstance();

Otherwise you need to involve the Reflection API to access and invoke the (unknown) methods/fields.


That said and unrelated to the actual problem:

properties.load(new FileInputStream(new File("ClassName.properties")));

Letting java.io.File rely on current working directory is recipe for portability trouble. Don't do that. Put that file in classpath and use ClassLoader#getResourceAsStream() with a classpath-relative path.

properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("ClassName.properties"));
Tuesday, June 1, 2021
 
redrom
answered 7 Months ago
76

Script added by setting the innerHTML property of an element doesn't get executed. Try creating a new div, setting its innerHTML, then adding this new div to the DOM. For example:

<html>
<head>
<script type='text/javascript'>
function addScript()
{
    var str = "<script>alert('i am here');</script>";
    var newdiv = document.createElement('div');
    newdiv.innerHTML = str;
    document.getElementById('target').appendChild(newdiv);
}
</script>
</head>
<body>
<input type="button" value="add script" onclick="addScript()"/>
<div>hello world</div>
<div id="target"></div>
</body>
</html>
Wednesday, June 2, 2021
 
AntoineB
answered 7 Months ago
45

This might be helpful:

function loadScript(url, callback){

    var script = document.createElement("script")
    script.type = "text/javascript";

    if (script.readyState){  //IE
        script.onreadystatechange = function(){
            if (script.readyState == "loaded" ||
                    script.readyState == "complete"){
                script.onreadystatechange = null;
                callback();
            }
        };
    } else {  //Others
        script.onload = function(){
            callback();
        };
    }

    script.src = url;
    document.getElementsByTagName("head")[0].appendChild(script);
}
Sunday, July 4, 2021
 
lewiguez
answered 6 Months ago
58

Sorry for answering my own question, but its been a while and we did come up with a solution. What we came up with was to load the javascript concurrently as text contained in a json object, and then used eval() once they were all loaded to execute them in the correct order. Concurrent load plus ordered execution. Depending on your use case you may not need the json. Roughly, here is some code that shows what we did -

// 'requests' is an array of url's to javascript resources
var loadCounter = requests.length;
var results = {};

for(var i = 0; i < requests.length; i++) {
   $.getJSON(requests[i], function(result) {
      results[result.id] = result;
      ...
      if(--loadCounter == 0) finish();
   });
}

function finish() {
  // This is not ordered - modify the algorithm to reflect the order you want
  for(var resultId in results) eval(results[resultId].jsString);
}
Tuesday, August 3, 2021
 
sathiya
answered 5 Months ago
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