com.tngtech.configbuilder.util.ConstructionHelper Maven / Gradle / Ivy

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The Config Builder creates fully configured instances of config classes, using values from various sources like properties files, command line arguments etc.

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package com.tngtech.configbuilder.util;

import com.tngtech.configbuilder.configuration.ErrorMessageSetup;
import com.tngtech.configbuilder.exception.ConfigBuilderException;
import com.tngtech.configbuilder.exception.NoConstructorFoundException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class ConstructionHelper {

    private final static Logger log = LoggerFactory.getLogger(ConstructionHelper.class);

    private final ErrorMessageSetup errorMessageSetup;

    public ConstructionHelper(ConfigBuilderFactory configBuilderFactory) {
        this.errorMessageSetup = configBuilderFactory.getInstance(ErrorMessageSetup.class);
    }

    public T getInstance(Class configClass, Object... objects) {
        try {
            Constructor tConstructor = findSuitableConstructor(configClass, objects);
            log.debug("found constructor - instantiating {}", configClass.getName());
            tConstructor.setAccessible(true);
            return tConstructor.newInstance(objects);
        } catch (InstantiationException | InvocationTargetException | IllegalAccessException e) {
            throw createConfigBuilderException(e);
        }
    }

    private ConfigBuilderException createConfigBuilderException(Exception e) {
        return new ConfigBuilderException(errorMessageSetup.getErrorMessage(e), e);
    }

    @SuppressWarnings("unchecked")
    private Constructor findSuitableConstructor(Class configClass, Object... objects) {
        log.debug("trying to find a constructor for {} matching the arguments of build()", configClass.getName());
        Constructor[] constructors = configClass.getDeclaredConstructors();
        for (Constructor constructor : constructors) {
            if (constructorIsMatching(constructor, objects)) {
                return constructor;
            }
        }
        throw new NoConstructorFoundException(errorMessageSetup.getErrorMessage(NoConstructorFoundException.class));
    }

    private boolean constructorIsMatching(Constructor constructor, Object... objects) {
        Class[] parameterTypes = constructor.getParameterTypes();
        if (parameterTypes.length != objects.length) {
            return false;
        } else {
            boolean constructorIsMatching = true;
            for (int i = 0; i < parameterTypes.length; i++) {
                constructorIsMatching &= parameterTypes[i].isAssignableFrom(objects[i].getClass());
            }
            return constructorIsMatching;
        }
    }
}