Question

我想减少我的代码，只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";
    }
}

在我的ArticleDAO中，我现在需要实现方法list / size：

@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应该如何？我想我不理解泛型的东西。

Answer 1

我不认为仿制药会在这里给你买任何东西。这甚至不会编译b / c T是未知的，你试图调用特定的方法（例如getId（））。

如果没有泛型，有几种方法可以做到这一点。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

如果这样做，您可以从方法中删除clazz参数。你不需要clazz.cast（）调用。

关于泛型的一句话，我通常会发现自己在使用泛型时无论类型如何都在做同样的事情。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。在您的上述情况中，您尝试根据类型执行不同的操作。它并不适用于泛型。事实上，每种类型做一些不同的事情通常意味着你可以很好地利用多态性。

Spring Controller / Service / Repository中的泛型

1 个答案: