java.lang.NullPointerException

Struts Problem Report
Struts has detected an unhandled exception:

Messages:
File: com/sterning/books/web/actions/BooksAction.java
Line number: 40


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Stacktraces
java.lang.NullPointerException
com.sterning.books.web.actions.BooksAction.list(BooksAction.java:40)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

package com.sterning.books.web.actions;



import java.util.Collection;



import com.sterning.books.model.Books;

import com.sterning.books.services.iface.IBooksService;

import com.sterning.commons.AbstractAction;

import com.sterning.commons.Pager;

import com.sterning.commons.PagerService;



public class BooksAction extends AbstractAction {

    

    private IBooksService booksService;

    private PagerService pagerService;

    

    private Books book;

    private Pager pager;

    

    protected Collection availableItems;

    protected String currentPage;

    protected String pagerMethod;

    protected String totalRows;

    protected String bookId;

    protected String queryName="1";

    protected String queryValue="1";

    protected String searchName;

    protected String searchValue;

    protected String queryMap;

    

    public String list() throws Exception {

        if(queryMap ==null||queryMap.equals("")){

        	           

        }else{

            String[] str=queryMap.split("~");

            this.setQueryName(str[0]);

            this.setQueryValue(str[1]);

        }

        

        //System.out.println("asd1"+this.getQueryValue());         

        //这里出错，网上的例子来的。。。。。： http://blog.csdn.net/zhicc/archive/2009/07/28/4386849.aspx

int totalRow=booksService.getRows(this.getQueryName(),this.getQueryValue());

        pager=pagerService.getPager(this.getCurrentPage(), this.getPagerMethod(), totalRow);

        

        this.setCurrentPage(String.valueOf(pager.getCurrentPage()));

        this.setTotalRows(String.valueOf(totalRow));

        availableItems=booksService.getBooks(this.getQueryName(),this.getQueryValue(),pager.getPageSize(), pager.getStartRow());

        

        this.setQueryName(this.getQueryName());

        this.setQueryValue(this.getQueryValue());

        

        this.setSearchName(this.getQueryName());

        this.setSearchValue(this.getQueryValue());

        

        return SUCCESS;         

    }