从Java应用程序生成Java类

Question

I am trying to create a data validation program that checks if a specific data type is valid by running each "type" (eg. name, age, gender) through its own validation method (each method is unique to its data type), the only problem is I want the application to be flexible to different data types and different amounts of data types.

Is there a way I can actually generate an entirely new Java application with methods for each type from the running Java application (for example "writing" a new class) during runtime once I have all the types?

Example Code:

public class JavaGen(){
    public static void main(String[] args){

        int dataLength = Integer.parseInt(JOptionPane.showInputDialog("Amount Of Data Types:"));
        String[] dataTypeList = new String[dataLength];

        //Fill up dataTypeList with user input
        writeJavaFile(dataTypeList);
    }

    public void writeJavaFile(String[] dataTypes){
        //Create the new class and its methods here using the array of dataTypes
    }
}

Which, for example, will then create a class of methods similar to this:

public class ActualClass(){
    public String validate'What The dataTypes[x] was'(String infoToValidate){
        if(etc etc){
            return "etc etc";
        }else{
            return "";
        }
    }
}

Answer 1

You can create, compile and instantiate a java class in runtime.

See this: http://www.java-tips.org/java-se-tips/java.lang/create-a-java-source-dynamically-compile-and.html

Some libraries: cglib Codemodel

Or you could use Nashorn. (javascript interpreter) I can imagine a use case where user defines complex validation in javascript and then this would be a good approach.

Although in your case I would not recommend any of the above and just write it in the code. Data types validation sounds like something you want to have hard-coded.

Answer 2

I can tell you right off that bat you are approaching a simple problem with an incredibly complex solution...

I would guess you are looking for the instanceof keyword, or perhaps an abstract validation class.

If you could be more specific with your intended functionality we could help you come up with a reasonable design pattern.

Directly to your question: Yes, you can generate and load classes in Java on the fly. It involves invoking the defineClass(String, byte[], int, int) method in the reflection package. As input to this function you have to provide a byte array of the class you are instantiating. This doesn't sound like the appropriate approach to this problem.