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我想精简我的代码以仅使用一个函数进行过滤。过滤应该使用 3 个不同的类：com.example.model.Category、com.example.model.Tag、java.util.Calendar。

这是我的控制器

@Controller
@RequestMapping( "/blog" )
public class BlogController
{
    @Autowired
    private ArticleService articleService;

    @Autowired
    private CategoryService categoryService;

    @Autowired
    private TagService tagService;

    private static final int PER_PAGE = 5;

    private static final int ARCHIVE_MONTHS = 12;

    @ModelAttribute
    public void addGlobalObjects( Map<String, Object> map )
    {
        map.put( "section", "blog" );

        SortedMap<Category, Integer> categories = new TreeMap<Category, Integer>();
        for ( Category category : categoryService.list() )
        {
            categories.put( category, articleService.size( category, Category.class ) );
        }

        Calendar cal = Calendar.getInstance();
        cal.set( Calendar.DAY_OF_MONTH, 1 );

        cal.add( Calendar.MONTH, ARCHIVE_MONTHS * -1 );

        SortedMap<Date, Integer> archive = new TreeMap<Date, Integer>();
        for ( int i = 0; i < ARCHIVE_MONTHS; ++i )
        {
            cal.add( Calendar.MONTH, 1 );
            archive.put( cal.getTime(), articleService.size( cal, Calendar.class ) );
        }

        SortedMap<Tag, Integer> tags = new TreeMap<Tag, Integer>();
        for ( Tag tag : tagService.list() )
        {
            tags.put( tag, articleService.size( tag, Tag.class ) );
        }

        map.put( "categories", categories );
        map.put( "archive", archive );
        map.put( "tags", tags );

        map.put( "categoriesSize", categoryService.size() );
        map.put( "tagsSize", tagService.size() );

        map.put( "date", new Date() );
    }

    @RequestMapping( "/index.html" )
    public String index( HttpServletRequest request, Map<String, Object> map )
    {
        return list( request, map, null, null );
    }

    @RequestMapping( "/archive/{date}.html" )
    public String archive( @PathVariable( "date" ) @DateTimeFormat( iso = ISO.DATE, style = "yyyy/MM" ) Date date, HttpServletRequest request, Map<String, Object> map )
    {
        Calendar cal = Calendar.getInstance();
        cal.setTime( date );

        return list( request, map, cal, Calendar.class );
    }

    private <T> String list( HttpServletRequest request, Map<String, Object> map, Object filterObject, Class<T> clazz )
    {
        int page = ServletRequestUtils.getIntParameter( request, "page", 1 );
        map.put( "articles", articleService.list( page * PER_PAGE - PER_PAGE, PER_PAGE, filterObject, clazz ) );
        map.put( "numPages", Math.ceil( articleService.size() / PER_PAGE ) );
        map.put( "currentPage", page );
        return "articles";
    }
}

现在在我的 ArticleDAO 中，我需要实现方法列表/大小：

@Repository
public class ArticleDAO extends BaseDAO<Article>
{
    public <T> List<Article> list( int offset, int limit, Object filterObject, Class<T> clazz )
    {
        Criteria c = doFilter( filterObject, clazz );

        if ( limit > 0 )
        {
            c.setFirstResult( offset );
            c.setMaxResults( limit );
        }

        return c.list();
    }

    public <T> Integer size( Object filterObject, Class<T> clazz )
    {
        Number ret = ( Number ) doFilter( filterObject, clazz ).setProjection( Projections.rowCount() ).uniqueResult();
        return ret.intValue();
    }

    private <T> Criteria doFilter( Object filterObject, Class<T> clazz )
    {
        Criteria criteria = sessionFactory.getCurrentSession().createCriteria( Article.class );

        if ( filterObject != null && clazz != null )
        {
            T filter = clazz.cast( filterObject );

            if ( filter instanceof Calendar )
            {
                // The method set(int, int) is undefined for the type T
                filter.set( Calendar.DAY_OF_MONTH, 1 );
                filter.set( Calendar.HOUR_OF_DAY, 0 );
                filter.set( Calendar.MINUTE, 0 );
                filter.set( Calendar.SECOND, 0 );
                // The method getTime() is undefined for the type T
                Date d1 = filter.getTime();

                // The method getActualMaximum(int) is undefined for the type T
                filter.set( Calendar.DAY_OF_MONTH, filter.getActualMaximum( Calendar.DAY_OF_MONTH ) );
                filter.set( Calendar.HOUR_OF_DAY, 23 );
                filter.set( Calendar.MINUTE, 59 );
                filter.set( Calendar.SECOND, 59 );
                Date d2 = filter.getTime();

                criteria.add( Restrictions.between( "creationDate", d1, d2 ) );
            }

            if ( filter instanceof Category )
            {
                // The method getId() is undefined for the type T
                criteria.createCriteria( "categories" ).add( Restrictions.eq( "id", filter.getId() ) );
            }

            if ( filter instanceof Tag )
            {
                // The method getId() is undefined for the type T
                criteria.createCriteria( "tags" ).add( Restrictions.eq( "id", filter.getId() ) );
            }
        }

        return criteria;
    }
}

ArticleDAO.doFilter 应该是什么样子？我想我不明白泛型的东西。

4

1 回答 1

2

我不认为仿制药在这里给你买任何东西。这甚至不会编译 b/c T 未知并且您正在尝试调用特定方法（例如 getId()）。

有几种方法可以在没有泛型的情况下做到这一点。最简单的方法是

 if ( filterObject instanceof Calendar ) {
   Calendar filterCal = (Calendar) filterObject;

   filterCal.set (Calendar.DAY_OF_MONTH, 1); // ... and so on

如果你这样做，你可以从你的方法中删除 clazz 参数。你不需要那个 clazz.cast() 调用。

只是关于泛型的一句话，当我做同样的事情时，我通常会发现自己使用泛型，而不管类型如何。例如，看起来您正在为 BaseDAO 成功使用泛型。无论类型如何，BaseDAO 都会保存、更新、删除等。在上述情况下，您正在尝试根据类型执行不同的操作。它并不真正适合泛型。事实上，对每种类型做不同的事情通常意味着你可以用多态性很好地做到这一点。

于 2012-07-28T14:36:38.193 回答