Custom Validator

package com.report.validator;

import com.report.excel.Employee;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

public class Validator {

    public List<Error> validate(Object object) {
        Error error = null;
        List<Error> errors = new ArrayList<>();
        Class<?> thisClass = null;
        try {
            thisClass = Class.forName(object.getClass().getName());
            Field[] aClassFields = thisClass.getDeclaredFields();
            for (Field f : aClassFields) {
                Field field = object.getClass().getDeclaredField(f.getName());
                field.setAccessible(true);
                Object value = field.get(object);
                System.out.println(value);
                if (value instanceof String) {
                    error = validateString(value.toString(), f.getName());
                    if (error != null) {
                        errors.add(error);
                    }

                } else if (value instanceof Integer) {
                    error = validateInt((Integer) value, f.getName());
                    if (error != null) {
                        errors.add(error);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return errors;
    }

    private Error validateString(String field, String fieldName) {
        Error error = null;
        if (field.isEmpty()) {
            error = new Error(fieldName, fieldName + " Shouldn't be empty");
        }
        if (field == null) {
            error = new Error(fieldName, fieldName + " Shouldn't be null");
        }
        return error;
    }

    private Error validateInt(Integer field, String fieldName) {
        Error error = null;
        if (field.intValue() == 0) {
            error = new Error(fieldName, fieldName + " Shouldn't be 0");
        }
        if (field == null) {
            error = new Error(fieldName, fieldName + " Shouldn't be null");
        }
        return error;
    }

    public static void main(String[] args) {
        Validator validator = new Validator();
        Employee employee = new Employee(0, "", "s@gmail.com", "IT");
        System.out.println(validator.validate(employee));


    }
}


package com.report.validator;

public class Error {

    private String fieldName;
    private String errorMessage;

    public String getFieldName() {
        return fieldName;
    }

    public void setFieldName(String fieldName) {
        this.fieldName = fieldName;
    }

    public String getErrorMessage() {
        return errorMessage;
    }

    public void setErrorMessage(String errorMessage) {
        this.errorMessage = errorMessage;
    }

    public Error() {
    }

    public Error(String fieldName, String errorMessage) {
        this.fieldName = fieldName;
        this.errorMessage = errorMessage;
    }

    @Override
    public String toString() {
        return "Error{" +
                "fieldName='" + fieldName + '\'' +
                ", errorMessage='" + errorMessage + '\'' +
                '}';
    }
}