pagedlistdatamodel.java

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/*
 * PagedListDataModel.java
 * 
 * Created on 2007-8-18, 6:37:54
 * 
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package biz.tbuy.common.page;

import javax.faces.model.DataModel;

/**
 *
 * @author Administrator
 */
public abstract class PagedListDataModel extends  DataModel{

    int  pageSize;
    int  rowIndex;
    DataPage page;

    /**
     * Create a datamodel that pages through the data showing the specified
     * number of rows on each page.
     */ 
    public PagedListDataModel(int pageSize) {
        super ();
        this .pageSize = pageSize;
        this .rowIndex = -1;
        this .page = null;
    } 
 
    /**
     * Not used in this class; data is fetched via a callback to the fetchData
     * method rather than by explicitly assigning a list.
     */ 
    public void setWrappedData(Object o) {
        if (o instanceof DataPage) {
            this .page = (DataPage)o;
        } else {
            throw new UnsupportedOperationException("setWrappedData");
        }
    }
 
    public int getRowIndex() {
        return rowIndex;
    }
 
    /**
     * Specify what the "current row" within the dataset is. Note that the
     * UIData component will repeatedly call this method followed by getRowData
     * to obtain the objects to render in the table.
     */ 
    public void setRowIndex(int index) {
        rowIndex = index;
    }
 
    /**
     * Return the total number of rows of data available (not just the number of
     * rows in the current page!).
     */ 
    public int getRowCount() {
        return getPage().getDatasetSize();
    }
    
    /**
     * Return a DataPage object; if one is not currently available then fetch
     * one. Note that this doesn't ensure that the datapage returned includes
     * the current rowIndex row; see getRowData.
     */
    private DataPage getPage() {
        if (page != null) {
            return page;
        } 
        int rowIndex = getRowIndex();
        int startRow = rowIndex;
        if (rowIndex == - 1) {
             // even when no row is selected, we still need a page
             // object so that we know the amount of data available. 
             startRow = 0;
        }
        // invoke method on enclosing class 
        page = fetchPage(startRow, pageSize);
        return page;
    }
 
    /**
     * Return the object corresponding to the current rowIndex. If the DataPage
     * object currently cached doesn't include that index then fetchPage is
     * called to retrieve the appropriate page.
     */ 
    public Object getRowData() {
        if (rowIndex < 0) {
            throw new IllegalArgumentException(
                "Invalid rowIndex for PagedListDataModel; not within page ");
        } 
        // ensure page exists; if rowIndex is beyond dataset size, then
        // we should still get back a DataPage object with the dataset size
        // in it 
        if (page == null) {
            page = fetchPage(rowIndex, pageSize);
        }
        int datasetSize = page.getDatasetSize();
        int startRow = page.getStartRow();
        int nRows = page.getData().size();
        int endRow = startRow + nRows;
        if (rowIndex >= datasetSize) {
            throw new IllegalArgumentException( "Invalid rowIndex " );
        }
        if (rowIndex < startRow) {
            page = fetchPage(rowIndex, pageSize);
            startRow = page.getStartRow();
        } else if (rowIndex >= endRow) {
            page = fetchPage(rowIndex, pageSize);
            startRow = page.getStartRow();
        }
        return page.getData().get(rowIndex - startRow);
    }
    public Object getWrappedData() {
        return page.getData();
    }
 
    /**
     * Return true if the rowIndex value is currently set to a value that
     * matches some element in the dataset. Note that it may match a row that is
     * not in the currently cached DataPage; if so then when getRowData is
     * called the required DataPage will be fetched by calling fetchData.
     */
    public boolean isRowAvailable() {
        DataPage page = getPage();
        if (page == null ) {
            return false;
        }
        int rowIndex = getRowIndex();
        if (rowIndex < 0) {
            return false;
        } else if (rowIndex >= page.getDatasetSize()) {
            return false;
        } else {
            return true;
        }
    } 
    /**
     * Method which must be implemented in cooperation with the managed bean
     * class to fetch data on demand.
     */ 
    public abstract DataPage fetchPage(int startRow, int pageSize);
}