Java Collection以获得最佳性能

Question

我有下面的代码片段，它获取区域（顶部或左侧）的所有可用菜单项，并添加用户可以访问ArrayList集合的小部件。 现在，getWidgetsByZone（zone）返回64个项目并对它们进行迭代。 我看到这种方法有一些性能滞后（在一个名为GlowRoot的工具中记录每个用户操作的时间轨迹）我不知道为什么。 我试图通过切换到其他最佳收集来提高性能。 有人可以帮助我为我的场景选择最佳集合吗？

AM使用JDK 7，Hibernate 3.6和Spring 3.1

这是DashboardService.getMenuItems（）实现

public List<IContentWidget> getMenuItems(String zone) {
        List<IContentWidget> widgets = new ArrayList<IContentWidget>();
        if (zone != null) {

            List<IPersistentEntityInstance> instances = getWidgetsByZone(zone);

            for (IPersistentEntityInstance instance : instances) {
                IContentWidget contentWidget = (IContentWidget) instance;
                if (contentWidget.getZones() == null) continue;

                // block widgets that should only show up in mobile / responsive ui
                if (contentWidget.getZones().contains(RESPONSIVE_VISIBLE)) continue;

                // Add widget only if the current user has read permission on the entity.
                if (contentWidget.getTargetItemScreen() != null || contentWidget.getTargetListScreen() != null) {
                    if (isAccessible(contentWidget)) {
                        widgets.add(contentWidget);
                    }
                }
                else {
                    widgets.add(contentWidget);
                }
            }
        }
        Collections.sort(widgets, new Comparator<IContentWidget>() {

            public int compare(IContentWidget o1, IContentWidget o2) {
                int i = o1.getOrderNum() - o2.getOrderNum();
                return i == 0 ? 0 : i < 0 ? -1 : 1;
            }

        });
        return widgets;
    }

DashboardService.isAccesible（）的实现

private boolean isAccessible(IContentWidget contentWidget) {
    boolean isWidgetAccessible = false;
    String permission = contentWidget.getDisplayPermission();
    if (permission != null) {
        isWidgetAccessible = authorizationService.userHasPermission(SecurityHelper.getAuthenticatedUser(),
                permission);
    }
    else {
        IBaseScreen screen = contentWidget.getTargetItemScreen() == null ? contentWidget.getTargetListScreen()
                : contentWidget.getTargetItemScreen();
        // return true when target screen is 'null', this means that target link cannot be secured because it is not
        // associated with any entity
        if (screen == null) {
            isWidgetAccessible = true;
        }
        else {
            IAccessEntry access = authorizationService.getAccessForEntityMetadata(screen.getEntityMetadata());

            // fetching metadata from entityMetadataService again to trigger population of facade
            if (screen instanceof IListScreen && access.getIsReadable()) {
                isWidgetAccessible = true;
            }
            else if (screen instanceof IItemScreen && access.getIsCreatable()) {
                isWidgetAccessible = true;
            }
        }
    }
    return isWidgetAccessible;
}

实现getWidgetsByZone方法

public List<IPersistentEntityInstance> getWidgetsByZone(String zone) {
    IEntityMetadata entity =  entityService.findEntityMetadataByName(ContentWidget.class.getSimpleName());
return entityService.runNamedQuery(entity, NamedQueryList.WIDGETS_BY_ZONE, new Object[] { zone });
    }

这是我的ContentWidget实体

@LocalOnly
@Entity
@EntityMetadataDefaults(editable = false)
@Audited
@NamedQueries({
    @NamedQuery(name = NamedQueryList.DASHBOARD_WIDGETS, query = "from ContentWidget where zones like '%dashboard%' and dashboardContexts.size = 0 order by orderNum", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }),
    @NamedQuery(name = NamedQueryList.WIDGETS_BY_ZONE, query = "from ContentWidget where zones like '%' || ? || '%' order by orderNum", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }),
    @NamedQuery(name = NamedQueryList.WIDGETS_BY_ZONE_ORDER_BY_NAME, query = "from ContentWidget where zones like '%' || ? || '%' order by displayName", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }),
    @NamedQuery(name = NamedQueryList.WIDGETS_BY_DASHBOARD_URL, query = "from ContentWidget where dashboardUrl like ? || '%'", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }),
    @NamedQuery(name = NamedQueryList.WIDGETS_BY_NAME, query = "from ContentWidget where name = ?", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }),
    @NamedQuery(name = NamedQueryList.WIDGETS_BY_CONTEXT, query = "from ContentWidget where zones like '%dashboard%' and ? in elements(dashboardContexts) order by orderNum", hints = {
            @QueryHint(name = "org.hibernate.cacheable", value = "true"),
            @QueryHint(name = "org.hibernate.cacheRegion", value = "Metadata") }) })
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE, region = "Metadata")
@EventDefaults({
        @EventHandlerDefaults(beanName = "contentWidgetPermissionCommand", eventType = EventTypeEnum.OnBeforeCreate),
        @EventHandlerDefaults(beanName = "contentWidgetPermissionCommand", eventType = EventTypeEnum.OnBeforeUpdate) })
@ReadPermission(name = AuthorizationService.ANONYMOUS_PERMISSION)
public class ContentWidget implements IContentWidget {
    private static final long       serialVersionUID = 1680304771254400928L;
    private String                  packageGuid;
    private Long                    id;

    private String                  name;                                   // unique name to reconcile imported data
    private String                  displayName;                            // used by UI
    private String                  description;                            // anchor title attribute
    private int                     orderNum;                               // universal ordering
    private String                  zones;                                  // csv: "top,left,dashboard,context,..."
    private String                  iconClass;
    private String                  displayPermission;

    // menu settings
    private IContentWidget          parent;

    private String                  targetUrl;

    private IListScreen             targetListScreen;
    private IItemScreen             targetItemScreen;
    private boolean                 isCacheable;
    private boolean                 isDivider;

    private boolean                 isPopup;

    private List<IEntityMetadata>   contextEntities;                        // for contextual menus
    protected IFilterDefinition     entityFilterDefinition;
    // dashboard settings
    private int                     dashboardWidth   = 1;
    private String                  dashboardUrl;
    private String                  dashboardWidgetType;
    private IListScreen             dashboardListScreen;
    private IItemScreen             dashboardItemScreen;
    private List<IEntityMetadata>   dashboardContexts;                      // for item screen dashboards

    private ISessionService         sessionService;
    @Autowired
    private IPassportContextService passportContextService;
    @Autowired
    private IReportingConfiguration reportingConfiguration;
    private Timestamp               createdAt;
    private Timestamp               updatedAt;
    private ICustomNamedQuery       menuCountQuery;
    private Set<IPassportContext>   passportContexts;
    }

性能跟踪更新：

GlowRoot中的方法性能跟踪如下

60.0% com.dc.core.presentation.presenter.impl.WebContentPresenter.getMenuHTML(WebContentPresenter.java:435)
50.0% com.dc.core.presentation.service.impl.DashboardService.getMenuItems(DashboardService.java:258)
30.0% com.dc.core.presentation.service.impl.DashboardService.isAccessible(DashboardService.java:382)

这是我的WebContentPresenter.getMenuHTML（）实现

public String getMenuHTML(String baseUrl, String zone, String cssClass, IPersistentEntityInstance entityInstance) {
    (line 435) List<IContentWidget> instances = dashboardService.getMenuItems(zone);
    StringBuffer html = new StringBuffer();

    if (instances == null || instances.isEmpty()) {
        html.append("&nbsp;");
    }
    else {
        Map<Long, List<IContentWidget>> treeData = new HashMap<Long, List<IContentWidget>>();
        for (IContentWidget instance : instances) {
            BeanWrapperImpl bean = new BeanWrapperImpl(instance);
            Object parent = bean.getPropertyValue("parent");
            Long parentId = -1L;
            if (passportContextService.getIsInContext(instance)) {
                if (parent != null) {
                    parentId = ((IContentWidget) parent).getId();
                }
                List<IContentWidget> children = treeData.get(parentId);
                if (children == null) {
                    children = new ArrayList<IContentWidget>();
                }
                children.add(instance);
                treeData.put(parentId, children);
            }
        }

        generateTreeHtml(html, treeData, -1L, baseUrl, "parent", entityInstance,
                authorizationService.userHasAdminPermission(SecurityHelper.getAuthenticatedUser()));
    }
    return String.format("<ul class=\"%s\">%s</ul>", cssClass, html.toString());
}

Answer 1

对于64个项目，集合之间的差异并不重要。 我宁愿调查IContentWidget方法调用。 你如何得到这些实例？ 也许每次调用getter时，都会对数据库执行查询？ 你能提供一些关于持久层的更多细节吗？

Answer 2

为了代码可读性，我更喜欢：

public List<IContentWidget> getMenuItems(String zone) {
    if(zone == null){
        return Collections. < IContentWidget > emptyList();
    }
    List<IContentWidget> widgets = new ArrayList<IContentWidget>();
    List<IPersistentEntityInstance> instances = getWidgetsByZone(zone);
    for (IPersistentEntityInstance instance : instances) {
        IContentWidget contentWidget = (IContentWidget) instance;
        if (contentWidget.getZones() == null || contentWidget.getZones().contains(RESPONSIVE_VISIBLE)) {
           continue;
        }
        // Add widget only if the current user has read permission on the entity.
        if (contentWidget.getTargetItemScreen() == null ||
            contentWidget.getTargetListScreen()== null) {
            widgets.add(contentWidget);continue;
        }
        if (isAccessible(contentWidget)) {
             widgets.add(contentWidget);
        }


    }
}
Collections.sort(widgets, new Comparator<IContentWidget>() {

    public int compare(IContentWidget o1, IContentWidget o2) {
        return o1.getOrderNum() - o2.getOrderNum();
    }

});
return widgets;
}

也改变

private boolean isAccessible(IContentWidget contentWidget) {
    boolean isWidgetAccessible = false;
    String permission = contentWidget.getDisplayPermission();
    if (permission != null) {
        return authorizationService.userHasPermission(SecurityHelper.getAuthenticatedUser(),
                permission);
    }
    else {
        IBaseScreen screen = contentWidget.getTargetItemScreen() == null ? contentWidget.getTargetListScreen()
                : contentWidget.getTargetItemScreen();
        // return true when target screen is 'null', this means that target link cannot be secured because it is not
        // associated with any entity
        if (screen == null) {
            return true;
        }
        else {
            IAccessEntry access = authorizationService.getAccessForEntityMetadata(screen.getEntityMetadata());

            // fetching metadata from entityMetadataService again to trigger population of facade
            if (screen instanceof IListScreen && access.getIsReadable()) {
                isWidgetAccessible = true;
            }
            else if (screen instanceof IItemScreen && access.getIsCreatable()) {
                isWidgetAccessible = true;
            }
        }
    }
    return isWidgetAccessible;
}