Create a shared variable instantly using a string class name

Question

I am using Google CSVReader, which requires a class name to create a parser. Using a parser, I read the CSV file in a list.

Consider this code:

ValueProcessorProvider provider = new ValueProcessorProvider();
    CSVEntryParser<A> entryParser = new AnnotationEntryParser<A>(A.class, provider);

    CSVReader<A> newExternalFileCSVReader = 
            new CSVReaderBuilder<A>(m_NewExternalFile).entryParser((CSVEntryParser<A>) entryParser).strategy(new CSVStrategy(',', '"', '#', true, true)).build();
    List<A> m_NewExternalFileData = newExternalFileCSVReader.readAll();

With this code, I can read the CSV file specific to class A.
I have several other classes: B, C, D, which all use the same code above, only with their corresponding class.

Could there be a function in which I pass the class name as a String that can create an instance of CSVReader / parser based on the input name String? where instead of creating 3 different sections of code (for classes B, C, D), I can use the same, just enter the corresponding class name?

Answer 1

You can use the factory pattern.

Create an interface and define inside the base methods for A, B, C, and D.

Then all classes A, B, C, and D must implement this interface.

public interface BaseInterface {
    // your methods
}

Then create a factory class in which you pass the identifier and it will correctly return your reader.

package a;

public final class Factory {

    // Not instantiable
    private Factory() {
        throw new AssertionError("Not instantiable");
    }

    public static CSVReader<your interface> getReader(String reader) {

        if ("A".equals(reader)) {
            return new CSVReader<A>();
        } else if ("B".equals(reader)) {
            return new CSVReader<B>();
        }
        // TODO create all your readers
    }
}

Now you can call the reader through your factory class as follows:

ValueProcessorProvider provider = new ValueProcessorProvider();
    CSVEntryParser<A> entryParser = new AnnotationEntryParser<A>(A.class, provider);

    CSVReader<your interface> newExternalFileCSVReader = 
            Factory("your reader type");
    List<your interface> m_NewExternalFileData = newExternalFileCSVReader.readAll();

Since you did not send classes A, B, C, and D, you need to configure this code, but after that I think you can do what you want.

Answer 2

You can do it:

public class MyCSVReader<T> {

    private Class<T> clazz;

    public MyCSVReader(Class<T> clazz) {
        this.clazz = clazz;
    }

    public List<T> readData(File file) {
        ValueProcessorProvider provider = new ValueProcessorProvider();
        CSVEntryParser<T> parser = new AnnotationEntryParser<T>(clazz, provider);
        CSVStrategy strategy = new CSVStrategy(',', '"', '#', true, true);
        CSVReaderBuilder builder = new CSVReaderBuilder<T>(file);
        CSVReader<T> reader = builder.entryParser(parser ).strategy(strategy).build();
        return reader.readAll();
    }
}

Then you would do:

MyCSVReader<A> readerA = new MyCSVReader<>(A.class);
List<A> data = readerA.readData(m_NewExternalFile);

And the same goes for any other classes.

EDIT: Maybe it would be useful to look for a type by file extension?

public class MyCSVReaderFactory {

    private static Map<String, MyCSVReader<?>> readersByFileExtension = new HashMap<>();

    // files with data for class A have extension .xta, etc.
    static {
        readersByFileExtension.put(".xta", new MyCSVReader<>(A.class));
        readersByFileExtension.put(".xtb", new MyCSVReader<>(B.class));
    }

    public MyCSVReader<?> create(String fileExtension) {
        MyCSVReader<?> reader = readersByFileExtension.get(fileExtension);
        if (reader == null) {
            throw new IllegalArgumentException("Unknown extension: " + fileExtension);
        }
        return reader;
     }
}

public List<?> doStuff(File file) {
    String fileExtension = getFileExtension(file);
    MyCSVReader<?> reader = MyCSVReaderFactory.create(fileExtension);
    return reader.readAll();
}

private String getFileExtension(File file) { 
    // TODO: implement this
}

(), A-D , .