java – 正确处理返回数据

我的意思是,看看JPA API中的find()方法,并返回正是他们在做什么.

/**
     * Find by primary key.
     * @param entityClass
     * @param primaryKey
     * @return the found entity instance or null
     *    if the entity does not exist
     * @throws IllegalStateException if this EntityManager has been closed.
     * @throws IllegalArgumentException if the first argument does
     *    not denote an entity type or the second
     *    argument is not a valid type for that
     *    entity's primary key
     */
    public <T> T find(Class<T> entityClass,Object primaryKey);

你可以在find中看到,我认为这与getCustomer()方法类似,如果没有找到,它将返回null,如果参数无效,则只会抛出IllegalArgumentException.

如果find()方法与getCustomer()不相似,则应该实现与getSingleResult()相同的行为：

/**
     * Execute a SELECT query that returns a single result.
     * @return the result
     * @throws EntityNotFoundException if there is no result
     * @throws NonUniqueResultException if more than one result
     * @throws IllegalStateException if called for a Java 
     *    Persistence query language UPDATE or DELETE statement
     */
    public Object getSingleResult();

如果没有找到结果,则会抛出EntityNotFoundException,如果发现多个实例,则为NonUniqueResultException,如果SQL为错误则为IllegalStateException.

你必须决定哪种行为最适合你.

getResultList()也是如此：

/**
 * Execute a SELECT query and return the query results
 * as a List.
 * @return a list of the results
 * @throws IllegalStateException if called for a Java 
 *    Persistence query language UPDATE or DELETE statement
 */   
public List getResultList();

如果没有找到,getResultList()将返回null,如果SQL是非法的则抛出异常.

通过遵循此行为,您是一贯的,您的用户将会了解图书馆的感觉.

一个备用的行为是返回一个空集合而不是null.这是Google Guava如何实现他们的API,这是真正的首选.但是,我喜欢一致性,仍然认为你应该尽可能接近标准来实现图书馆.

资源

Joshua Bloch made a video explaining how to design a good API and why it matters.