基于rich:datascroller和rich:dataTable的分页查询实现

最新推荐文章于 2019-04-06 21:45:29 发布

原创最新推荐文章于 2019-04-06 21:45:29 发布 · 139 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#JSF #Cache

Java 专栏收录该内容

24 篇文章

订阅专栏

本文介绍了一种在JSF中实现高效数据分页的方法。通过自定义BaseExtendedDataModel类和PeopleListExtendedDataModel类，结合rich:datascroller和rich:dataTable组件，实现了真正的数据层分页查询。这种方法不仅提高了应用程序的性能，还减少了服务器负载。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

一般来说，基于rich:datascroller和rich:dataTable进行配合，马上就实现了表格及分页，但这种分布是一种“伪分页”，即：只是表现层分页，在数据层并没有进行分页查询。

下面给出一个我在使用的支持数据层分布查询的方法：

基类：

public abstract class BaseExtendedDataModel<T, ID extends Serializable> extends ExtendedDataModel {  
    @Logger  
    private Log log;  
  
    public List<T> listRow = null;  
    private int firstRow_old = 0;  
  
    private ID currentId;  
    private Map<ID, T> wrappedData = new HashMap<ID, T>();  
    private Long rowCount; // better to buffer row count locally  
  
    public abstract Long getCount();  
  
    public abstract List<T> getList(Integer firstRow, Integer maxResults);  
  
    public abstract T findById(ID id);  
  
    public void wrap(FacesContext context, DataVisitor visitor, Range range, Object argument, List<T> list) throws IOException {  
         wrappedData = new HashMap<ID, T>();  
        for (T row : list) {  
             ID id = null;  
            try {  
                 id = (ID) PropertyUtils.getProperty(row, "id");  
             } catch (Exception e) {  
                 e.printStackTrace();  
                throw new RuntimeException(e);  
             }  
            // wrappedKeys.add(id);  
             wrappedData.put(id, row);  
             visitor.process(context, id, argument);  
         }  
     }  
  
    public boolean hasById(ID id) {  
        return wrappedData.get(id) != null;  
     }  
  
    @Override  
    public void walk(FacesContext context, DataVisitor visitor, Range range, Object argument) throws IOException {  
        int firstRow = ((SequenceRange) range).getFirstRow();  
        int maxResults = ((SequenceRange) range).getRows();  
        if (firstRow != firstRow_old || listRow == null){  
             listRow = getList(firstRow, maxResults);  
             firstRow_old = firstRow;  
         }  
         wrap(context, visitor, range, argument, listRow);  
     }  
  
    /*
      * This method normally called by Visitor before request Data Row.
      */  
    @Override  
    public void setRowKey(Object key) {  
        this.currentId = (ID) key;  
     }  
  
    @Override  
    public int getRowCount() {  
        if (rowCount == null)  
            return (rowCount = this.getCount()).intValue();  
        else  
            return rowCount.intValue();  
     }  
  
    @Override  
    public boolean isRowAvailable() {  
        if (currentId == null) {  
            return false;  
         } else {  
            return hasById(currentId);  
         }  
     }  
  
    /**
      * This is main way to obtain data row. It is intensively used by framework. We strongly recommend use of local cache in that method.
      */  
    @Override  
    public Object getRowData() {  
        if (currentId == null) {  
            return null;  
         } else {  
             T ret = wrappedData.get(currentId);  
            if (ret == null) {  
                 ret = this.findById(currentId);  
                 wrappedData.put(currentId, ret);  
                return ret;  
             } else {  
                return ret;  
             }  
         }  
     }  
  
    /**
      * Unused rudiment from old JSF staff.
      */  
    @Override  
    public Object getWrappedData() {  
        throw new UnsupportedOperationException();  
     }  
    private int rowIndex = 0;  
    @Override  
    public int getRowIndex() {  
        //throw new UnsupportedOperationException();  
        return rowIndex;  
     }  
  
    @Override  
    public void setRowIndex(int rowIndex) {  
        //throw new UnsupportedOperationException();  
        this.rowIndex = rowIndex;  
     }  
  
    @Override  
    public void setWrappedData(Object data) {  
        throw new UnsupportedOperationException();  
     }  
  
    @Override  
    public Object getRowKey() {  
        if (true)  
            throw new UnsupportedOperationException();  
        return currentId;  
     }  
  
}

数据列表类

public class PeopleListExtendedDataModel extends BaseExtendedDataModel<People, Long>{  
...  
    @Override  
    public People findById(Long id) {  
        return entityManager.find(People.class, id);  
     }  
    @Override  
    public Long getCount() {  
        return (Long)createQuery(true).getSingleResult();  
     }  
  
    @Override  
    public List<People> getList(Integer firstRow, Integer maxResults) {  
        return createQuery(false).setFirstResult(firstRow).setMaxResults(maxResults).getResultList();  
     }  
  
...  
  
}

页面代码：

<rich:datascroller align="left"  for="peopleList" maxPages="20" rendered="#{peopleListExtendedDataModel.size>20}"/>  
<rich:dataTable width="100%" id="peopleList" rows="20" columnClasses="col"  
    value="#{peopleListExtendedDataModel}" var="people">