How can I read Class and objects name from File using Java Reflection?

Question

I have a file named Objects.dat and I want to read the Class name and objects name from that file using Java Reflection. I'm able to read from another Java class but not from the file. How can I solve this?

Java Class

public class EmployeeInfo {
    private String username = "John";
    private int userage = 23;
}

Objects.dat contains the same text as Java class.

Class Reader

public class FileRd {
    public static void main(String[] args)  {
            try {
                Class cls = Class.forName("EmployeeInfo");
                Object obj = cls.newInstance();

                System.out.println("Class Name-->"+obj.getClass());
                Field[] fields = cls.getDeclaredFields();
                for( int i = 0 ; i < fields.length ; i++ ) {
                    fields[i].setAccessible(true);
                    System.out.println("Name-->"+fields[i].getName());
                }
            }
            catch( Exception e ) { e.printStackTrace(); }
    }
}

The above code works for the Java class but I want to input the file like and read -

FileInputStream fin = new FileInputStream("D:\\Objects.bat");

and perform the above functionally but I failed to do that.

Are you sure you want reflection? I think serialization would be the way to go here. — markspace
– markspace, Commented Apr 26, 2018 at 16:22
Sorry actually I don't have any idea about JAVA Reflection so i searched for last couple of hours and i just got this idea. If you can suggest this will be helpful for me . Thanks. — Daniel
– Daniel, Commented Apr 26, 2018 at 16:25
Some basic info is here: oracle.com/technetwork/articles/java/javaserial-1536170.html (Sorry for that previous link, this one is actually on point.) — markspace
– markspace, Commented Apr 26, 2018 at 16:32
Isn't it possible to read class and object name from the input file instead of reading from a JAVA class ? — Daniel
– Daniel, Commented Apr 26, 2018 at 16:40
I think it might be "possible" but I don't see how that's useful or a good idea. — markspace
– markspace, Commented Apr 26, 2018 at 16:44

Marcos Vasconcelos · Accepted Answer · 2018-04-26 18:25:17Z

1

You need a Custom classloader for such, if the file is already compiled (if not you can use javac tool to compile it with classpath or an Bytecode tool like ASM or Javassist).

Then you use your ClassLoader to load the file(.class) and findClass.

answered Apr 26, 2018 at 18:25

Marcos Vasconcelos

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Jackkobec · Accepted Answer · 2018-04-26 16:27:18Z

0

Maybe Serialization / Deserialization is the better way than save Java code at the file.

answered Apr 26, 2018 at 16:27

Jackkobec

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5 Comments

Daniel Over a year ago

Isn't it possible to read class and object name from the input file instead of reading from a JAVA class ?

Jackkobec Over a year ago

You can parse it with regex or substring: If you read file line by line: try parse with substring: string className = line.subString(line.indexOf("class"), line.indexOf("}")).trim();

Daniel Over a year ago

but how could i got the objects name and type in this way ?

Jackkobec Over a year ago

Only for class name: String input = "public class Test { " + "\ncode;" + "\ncode;" + "\n}"; String className = input.substring(input.indexOf("class") + "class".length(), input.indexOf("{")).trim(); System.out.println(className);

Daniel Over a year ago

But I also need the Objects name and type from that file. :(

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