获取Java中类的字段名称

Question

I am trying to generate a CSV mapping for the fields of a class in Java in an automatic way since I need to use it several times.

I have the following method for trying to get the field names: (where CSV header is something like "DB_NAME|FIELD_NAME|ADDITIONAL_F1|ADDITIONAL_F2")

package util;

import java.lang.reflect.Field;

public class CsvAttributesMappingGenerator {
public static String generateCsvAttributesMapping(Class<?> model) {

    StringBuilder csvBuilder = new StringBuilder();

    Field[] fieldList = model.getDeclaredFields();
    for (Field field : fieldList) {
        //field.setAccessible(true);
        csvBuilder.append(field.getName().replaceAll("(.)(\\p{Upper})", "$1_$2").toUpperCase());
        csvBuilder.append("|");
        csvBuilder.append(field.getName());
        csvBuilder.append("||\n");
    }
    return formatOutput(csvBuilder.toString());
}

private static String formatOutput(String classText) {
    String delimiter = "\n******************************\n";
    return String.format("%s%s%s", delimiter, classText, delimiter);
}

}

and a test call like:

import objects.User;
import org.junit.Test;
import util.CsvAttributesMappingGenerator;

public class CsvAttributesMappingGeneratorTest {

@Test
public void testGenerationWithObject() {
    System.out.println(CsvAttributesMappingGenerator.generateCsvAttributesMapping(User.class));
}
}

The object to be parsed has the following structure: package objects;

public class User {
private String userName;
private String userEmail;
private int userAge;
private String otherDetails;
// getters, setters and all args constuctor here
}

The output should have multiple rows like FIELD_NAME|fieldName|| where the camel cased item should be collected from the given class. I attempted to use Java Reflection API as I have seen on several examples but I get a strange String output instead. (not the serialized @randomCharsLikeName). Tried toString() and other dirty tricks but nothing worked.

Can someone tip me up a little with this? Or at least tell me if it is possible to do what I tried? Thanks in advance!

EDIT: the current code prototype presented in the question works in an isolated environment (separate new project) and displays the expected output. It does not work though integrated within the whole application I am trying to integrate it into. I will keep researching and let you know the root cause (in the real app I am using also lombok for the classes (

@AllArgsConstructor, @NoArgsConstructor, @Data, @ToString

), but I do not honestly think that this might be an issue while using Reflection)

Answer 1

I found the issue in the meanwhile. While I was play-prototyping the generator, I used:

csvBuilder.append(field.getClass().getName().replaceAll("(.)(\\p{Upper})", "$1_$2").toUpperCase());

which produced outputs like JAVA.LANG.REFLECT._FIELD|java.lang.reflect.Field||

Since I simply forgot that I actually improved it to use actual class object as a parameter to the function. Before asking the question I made some Sonar fixes to the code and did not notice that I fixed a WARN to remove the .getClass() method invocation since I already pass in a class (I thought it would not make a difference since it is just a warning). Moral tip of the day - NEVER EVER ignore warnings.

So the code snippets presented in the question work fine now in an isolated dummy project and also integrated within a more complex project, using the fixed line:

csvBuilder.append(field.getName().replaceAll("(.)(\\p{Upper})", "$1_$2").toUpperCase());

Also as someone suggested in the comments, the field.setAccessible(true); can be removed since it is useless for the purpose of the method.