类是否可以继承超类的注解 [英] Is it possible for class to inherit the annotations of the super class

问题描述

我正在使用 Spring Framework 事务注释进行事务管理，并且我有一个 abstract class 注释 @Transactional，如下所示:

I am using Spring Framework transactional annotations for transaction managing and I have an abstract class annotated @Transactional as seen below:

package org.tts.maqraa.service;

import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import javax.persistence.EntityManager;
import javax.persistence.EntityNotFoundException;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceContextType;
import javax.persistence.Query;

import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Parts of this code have been copied from JARVANA site.
 * 
 * @author Younis alomoush
 * 
 */
@Transactional(propagation=Propagation.REQUIRED)
public abstract class AbstractMaqraaService implements MaqraaService {


    private Logger logger = LoggerFactory.getLogger(this.getClass());


    private int defaultMaxResults = DEFAULT_MAX_RESULTS;

    @PersistenceContext(type=PersistenceContextType.TRANSACTION)
    private EntityManager em;
    /**
     * The {@link EntityManager} which is used by all query manipulation and
     * execution in this DAO.
     * 
     * @return the {@link EntityManager}
     */
    public  EntityManager getEntityManager(){

        return em;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#getTypes()
     */
    public abstract Set<Class<?>> getTypes();

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#store(java.lang.Object)
     */
    @Transactional(propagation = Propagation.REQUIRED)
    public <T extends Object> T store(T toStore) {
        return getEntityManager().merge(toStore);

    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#remove(java.lang.Object)
     */
    @Transactional(propagation = Propagation.REQUIRED)
    public void remove(Object toRemove) {
        toRemove = getEntityManager().merge(toRemove);
        getEntityManager().remove(toRemove);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#flush()
     */
    @Transactional(propagation = Propagation.REQUIRED)
    public void flush() {
        getEntityManager().flush();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#refresh(java.lang.Object)
     */
    @Transactional(propagation = Propagation.SUPPORTS)
    public void refresh(Object o) {
        try {
            if (o != null) {
                if (o instanceof java.util.Collection) {
                    for (Iterator<?> i = ((Collection<?>) o).iterator(); i
                            .hasNext();) {
                        try {
                            refresh(i.next());
                        } catch (EntityNotFoundException x) {
                            // This entity has been deleted - remove it from the
                            // collection
                            i.remove();
                        }
                    }
                } else {
                    if (getTypes().contains(o.getClass())) {
                        getEntityManager().refresh(o);
                    }
                }
            }
        } catch (EntityNotFoundException x) {
            // This entity has been deleted
        }
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#setDefaultMaxResults(int)
     */
    @Transactional(propagation = Propagation.SUPPORTS)
    public void setDefaultMaxResults(int defaultMaxResults) {
        this.defaultMaxResults = defaultMaxResults;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#getDefaultMaxResults()
     */
    public int getDefaultMaxResults() {
        return defaultMaxResults;
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByNameSingleResult(java
     * .lang.String)
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> T executeQueryByNameSingleResult(String queryName) {
        return (T) executeQueryByNameSingleResult(queryName, (Object[]) null);
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByNameSingleResult(java
     * .lang.String, java.lang.Object[])
     */

    @SuppressWarnings("unchecked")
    public <T extends Object> T executeQueryByNameSingleResult(
            String queryName, Object... parameters) {
        Query query = createNamedQuery(queryName, DEFAULT_FIRST_RESULT_INDEX,
                1, parameters);
        return (T) query.getSingleResult();
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByName(java.lang.String)
     */
    public <T extends Object> List<T> executeQueryByName(String queryName) {
        return executeQueryByName(queryName, DEFAULT_FIRST_RESULT_INDEX,
                getDefaultMaxResults());
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByName(java.lang.String,
     * java.lang.Integer, java.lang.Integer)
     */

    public <T extends Object> List<T> executeQueryByName(String queryName,
            Integer firstResult, Integer maxResults) {
        return executeQueryByName(queryName, firstResult, maxResults,
                (Object[]) null);
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByName(java.lang.String,
     * java.lang.Object[])
     */

    public <T extends Object> List<T> executeQueryByName(String queryName,
            Object... parameters) {
        return executeQueryByName(queryName, DEFAULT_FIRST_RESULT_INDEX,
                getDefaultMaxResults(), parameters);
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQueryByName(java.lang.String,
     * java.lang.Integer, java.lang.Integer, java.lang.Object[])
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> List<T> executeQueryByName(String queryName,
            Integer firstResult, Integer maxResults, Object... parameters) {
        Query query = createNamedQuery(queryName, firstResult, maxResults,
                parameters);
        return query.getResultList();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#createNamedQuery(java.lang.String,
     * java.lang.Integer, java.lang.Integer)
     */

    public Query createNamedQuery(String queryName, Integer firstResult,
            Integer maxResults) {
        return createNamedQuery(queryName, firstResult, maxResults,
                (Object[]) null);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#createNamedQuery(java.lang.String,
     * java.lang.Integer, java.lang.Integer, java.lang.Object[])
     */

    public Query createNamedQuery(String queryName, Integer firstResult,
            Integer maxResults, Object... parameters) {
        Query query = getEntityManager().createNamedQuery(queryName);
        if (parameters != null) {
            for (int i = 0; i < parameters.length; i++) {
                query.setParameter(i + 1, parameters[i]);
            }
        }

        query.setFirstResult(firstResult == null || firstResult < 0 ? DEFAULT_FIRST_RESULT_INDEX
                : firstResult);
        if (maxResults != null && maxResults > 0)
            query.setMaxResults(maxResults);

        return query;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#executeQuery(java.lang.String,
     * java.lang.Integer, java.lang.Integer, java.lang.Object[])
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> List<T> executeQuery(String queryString,
            Integer firstResult, Integer maxResults, Object... parameters) {
        Query query = createQuery(queryString, firstResult, maxResults,
                parameters);
        return query.getResultList();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#executeQuery(java.lang.String,
     * java.lang.Object[])
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> List<T> executeQuery(String queryString,
            Object... parameters) {
        Query query = createQuery(queryString, DEFAULT_FIRST_RESULT_INDEX,
                getDefaultMaxResults(), parameters);
        return query.getResultList();
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQuerySingleResult(java.lang.
     * String)
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> T executeQuerySingleResult(String queryString) {
        return (T) executeQuerySingleResult(queryString, (Object[]) null);
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.skyway.spring.util.dao.JpaDao#executeQuerySingleResult(java.lang.
     * String, java.lang.Object[])
     */
    @SuppressWarnings("unchecked")
    public <T extends Object> T executeQuerySingleResult(String queryString,
            Object... parameters) {
        Query query = createQuery(queryString, DEFAULT_FIRST_RESULT_INDEX, 1,
                parameters);
        return (T) query.getSingleResult();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#createQuery(java.lang.String,
     * java.lang.Integer, java.lang.Integer)
     */

    public Query createQuery(String queryString, Integer firstResult,
            Integer maxResults) {
        return createQuery(queryString, firstResult, maxResults,
                (Object[]) null);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.skyway.spring.util.dao.JpaDao#createQuery(java.lang.String,
     * java.lang.Integer, java.lang.Integer, java.lang.Object[])
     */
    public Query createQuery(String queryString, Integer firstResult,
            Integer maxResults, Object... parameters) {
        Query query = getEntityManager().createQuery(queryString);
        if (parameters != null) {
            for (int i = 0; i < parameters.length; i++) {
                query.setParameter(i + 1, parameters[i]);
            }
        }

        query.setFirstResult(firstResult == null || firstResult < 0 ? DEFAULT_FIRST_RESULT_INDEX
                : firstResult);
        if (maxResults != null && maxResults > 0)
            query.setMaxResults(maxResults);

        return query;
    }

    public final void log(LogLevel logLevel, String message,
            Object... messageParam) {

        switch (logLevel) {
        case TRACE:
            if (logger.isTraceEnabled()) {

                logger.trace(message, messageParam);
            }

            break;

        case DEBUG:
            if (logger.isDebugEnabled()) {

                logger.debug(message, messageParam);
            }
            break;

        case INFO:
            if (logger.isInfoEnabled()) {

                logger.info(message, messageParam);
            }
            break;

        case WARN:
            if (logger.isWarnEnabled()) {

                logger.warn(message, messageParam);
            }
            break;

        case ERROR:
            if (logger.isErrorEnabled()) {

                logger.error(message, messageParam);
            }
            break;

        default:
            throw new IllegalArgumentException("Log Level is not defined: "
                    + logLevel);

        }

    }

    public final void log(LogLevel logLevel,  String message, Throwable throwable) {

        switch (logLevel) {
        case TRACE:
            if (logger.isTraceEnabled()) {

                logger.trace(message, throwable);
            }

            break;

        case DEBUG:
            if (logger.isDebugEnabled()) {

                logger.debug(message, throwable);
            }
            break;

        case INFO:
            if (logger.isInfoEnabled()) {

                logger.info(message, throwable);
            }
            break;

        case WARN:
            if (logger.isWarnEnabled()) {

                logger.warn(message, throwable);
            }
            break;

        case ERROR:
            if (logger.isErrorEnabled()) {

                logger.error(message, throwable);
            }
            break;

        default:
            throw new IllegalArgumentException("Log Level is not defined: "
                    + logLevel);

        }

    }


    public enum LogLevel{

        TRACE, DEBUG, INFO, WARN, ERROR;

    }
}

另外，我还有一个具体的类

Also, i have another concrete class

package org.tts.maqraa.service;

import java.lang.annotation.Annotation;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.tts.maqraa.data.Student;


public class StudentsService extends AbstractMaqraaService {

    @Override
    public Set<Class<?>> getTypes() {
        Set<Class<?>> set = new HashSet<Class<?>>();
        set.add(Student.class);
        return set;
    }

    public Student registerStudent(Student student) {
        Annotation [] annotation = StudentsService.class.getAnnotations();
        System.out.println(annotation);
        return this.store(student);
    }

    public Student editStudent(Student student){
        return this.store(student);
    }

    public void deregisterStudent(Student student){
        this.remove(student);
    }

    public List<Student> findAllStudents(){
        return this.executeQueryByName("Student.findAll");
    }

}

如果您注意到方法 register student 已经提供了用于检查注释的代码，其中我真正找到了 @Transactional 注释.

If you notice that the method register student has already provided code for examine the annotations where I really find the @Transactional annotation.

这是一个矛盾，我有另一个链接谈论注释的继承，它说根本没有继承.

That's a contradiction where I have another link talks about inheritance of annotations and it says that there is no inheritance at all.

查看此链接:http://fusionsoft-online.com/articles-java-注释.php

谁能帮我解决这个矛盾?

Can anyone help me to solve this contradiction ?

推荐答案

注解继承的工作原理与方法或字段的继承基本相同.

Annotation inheritance works basically the same way as inheritance of methods or fields.

由于只能通过反射访问注解，所以Class中有两个基本方法:

Since you can access annotations only through reflection, there are two basic methods in Class:

• getAnnotations() 返回当前类及其超类的所有注解
• getDeclaredAnnotations() 返回当前类的所有注解

• getAnnotations() returns all annotations on the current class and its super classes
• getDeclaredAnnotations() returns all annotations on the current class

您链接的文章谈到的问题是 Method#getAnnotation(...) 访问了该方法已在其中定义的类的 declaredAnnotations()，其中如上所述，只返回在该类中定义的注解，而不返回超类的注解.

The problem the article you linked talks about is that Method#getAnnotation(...) accesses declaredAnnotations() of the class the method has been defined in, which as stated above only returns the annotations defined in that class and not those of the super classes.

这意味着，如果您覆盖用 @Transactional 注释的方法之一，则必须在那里添加注释(或者如果框架也查看类注释，它应该找到 @Transactional 在 AbstractMaqraaService 上声明.

This means that if you override one of the methods annotated with @Transactional you'd have to add the annotation there (or if the frameworks also looks in the class annotation it should find the @Transactional declared on AbstractMaqraaService).

这篇关于类是否可以继承超类的注解的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！