Parsing code from parameter file through content

[PDavane]

code_parser=System.out.println("Complex Java code to be passed through parameter file".toUpperCase())

I want to pass code in standard talend jobs as a filter from parameter file through Context which can be changed later on as per business need. This Java String has to be converted into executable code in Talend.

[Anonymous · Accepted solution]

I'll be honest, I am not sure why you would want to do this, but I was fascinated to see if I could. There is a big problem with compiling code that uses classes that do not exist. So this has to be done in such a way that class specifics (of the class you want to compile at runtime) are minimised.

The job I wrote to do this look like this.....

 

The tFixedFlowInput is where I am supplying the code for this example. The code is just passed in as a String. The code is being written to a file that I am calling myCode.java using the tFileOutputRaw. That's pretty simple enough. FYI the code that I am passing to the file looks like this.....

public class MyCode {

String data1;

String data2;

public MyCode(String data1, String data2){ 

this.data1 = data1;

this.data2 = data2;

}

public String toString(){

return data1 + " " + data2 + " how are you?";

}

}

It is added to the tFixedFlowInput as such (note the escaped quotes as quotes are used in Java to denote a String)....

"public class MyCode {String data1;String data2;public MyCode(String data1, String data2){ this.data1 = data1;this.data2 = data2;}public String toString(){return data1 + \" \" + data2 + \" how are you?\";}}"

The next step is to compile the file that we have just created and run it. FYI I found the basis of this code here ....

https://www.netjstech.com/2016/10/how-to-compile-java-program-at-runtime.html

I set up the tJavaFlex to have a single column output. This is called "class_data". This is printed using the tLogRow.

The code in the tJavaFlex can be seen below with notes....

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

// Code to compile - Supplied to the tFileOutputRaw above

int result = compiler.run(null, null, null, "/Users/richardhall/Documents/MyCode.java");

// Path of the class

File classesDir = new File("/Users/richardhall/Documents");

// Load and instantiate compiled class.

URLClassLoader classLoader;

try {

 // Loading the class 

  classLoader = URLClassLoader.newInstance(new URL[] { classesDir.toURI().toURL() });

    Class<?> clazz = Class.forName("MyCode", true, classLoader);

    //The following is a hack to get this to be of any use. What I am doing here is

    //using the constructor of the class that I have created in the previous subjob to

    //act as the only way of receiving variables. 

Class[] cArg = new Class[2]; //Our constructor has 2 arguments

cArg[0] = String.class; //First argument is of *object* type String

cArg[1] = String.class; //Second argument is of *object* type String

String s1 = "Hello";

String s2 = "World";

//The following code instantiates the new class and immediately calls the toString() method

//This is because at compile time, this class we are building does not exist. So I have only access to

//methods that exist on the base Object class. The toString() method has been overridden to return 

//the result.

row2.class_data = clazz.getDeclaredConstructor(cArg).newInstance(s1, s2).toString();

} catch (MalformedURLException e) {

  // TODO Auto-generated catch block

  e.printStackTrace();

} catch (ClassNotFoundException e) {

  // TODO Auto-generated catch block

  e.printStackTrace();

} catch (IllegalAccessException e) {

  // TODO Auto-generated catch block

  e.printStackTrace();

} catch (InstantiationException e) {

  // TODO Auto-generated catch block

  e.printStackTrace();

} 

With this code in place, you can modify the Java code used by the tFixedFlowInput and get a different result. To start with the code is initially concatenating the first constructor param String with the second, then adding " how are you?". If you have put together this job to try this out, the first Java class is below.....

"public class MyCode {String data1;String data2;public MyCode(String data1, String data2){ this.data1 = data1;this.data2 = data2;}public String toString(){return data1 + \" \" + data2 + \" how are you?\";}}"

......to test this with another Java class, just replace what is in the tFixedFlowInput with this....

"public class MyCode {String data1;String data2;public MyCode(String data1, String data2){ this.data1 = data1;this.data2 = data2;}public String toString(){return data1 + \" \" + data2 + \" did you see how this worked?\";}}"

As I said, I can't see a great many uses for this. It would be easier to alter the flow of code in a different way. But if you really want to do this and have a use case that maybe I am not thinking of, you can try something like this.

[PDavane]

Hello rhall. Thank you for the help. Can you please attach zipped export of this job.

[Anonymous]

Hi @Pooja D​, apologies but I am afraid I do not have this job anymore. I wrote it and threw it away. However, all of the information you need is included in the post.