大家都知道Struts是一種基于MVC的結構，而這個MVC又怎么樣理解呢？書上闡述的一般都很詳細，而我的理解很直白，我們可以把業務邏輯放到每個JSP頁面中，當你訪問一個JSP頁面的時候，就可以看到業務邏輯得到的結果，而把這些業務邏輯與HTML代碼夾雜到了一起，一定會造成一些不必要的麻煩，可以不可以不讓我們的業務邏輯和那些HTML代碼夾雜到一起呢？多少得攙雜一些，那干脆，盡量少的吧，于是我們可以嘗試著把業務邏輯的運算過程放到一個Action里，我們訪問這個Action，之后Action執行業務邏輯，最后把業務邏輯的結果放到request中，并將頁面請求轉發給一個用于顯示結果的jsp頁面，這樣，這個頁面就可以少去很多的業務邏輯，而只是單純的去顯示一些業務邏輯計算結果的頁面而已。這時的Action稱為控制器，JSP頁可以叫做視圖了，而控制器操作的業務對象，無非就應該叫模型了！
從上面的話，我們來分析一下當我們要做一個分頁時所需要的部分，而在這之前，我們先看看他們的執行過程吧，首先我們第一次請求訪問一個頁面，它會把所有記錄的前N條顯示給我們，之后計算是否有下一頁，等類似的信息，當我們點下一頁的時候，就獲取下一頁的信息，我們還可以添加一個搜索，比如我們用于顯示學生的，可以安學生姓名查找，學號查找，班級查找。而對于顯示的對象，我們一般也都會封裝為javabean，所以用于放置查詢結果的容器是不定的，而這時，我們就需要用泛型來提升我們的代碼效率！
首先我們寫一個用于分頁顯示的javabean：
package com.boya.subject.model;
import java.util.Vector;
public class Page<E>
{
??? private int current = 1;??????? //當前頁
??? private int total = 0;???????? //總記錄數
??? private int pages = 0;??? //總頁數
??? private int each = 5;???????? //每頁顯示
??? private int start = 0;????? //每頁顯示的開始記錄數
??? private int end = 0;?????? //每頁顯示的結束記錄數
??? private boolean next = false;??????? //是否有下一頁
??? private boolean previous = false;? //是否有上一頁
??? private Vector<E> v = null;???
//存放查詢結果的容器
??? public Page( Vector<E> v ,int per)
??? {
??????? this.v = v;
??????? each = per;
??????? total = v.size();?? //容器的大小就是總的記錄數
??????? if ( total % each == 0 )
??????????? pages = total / each;?????? //計算總頁數
??????? else
??????????? pages = total / each + 1;
??????? if ( current >= pages )
??????? {
??????????? next = false;
??????? }
??????? else
??????? {
??????????? next = true;
??????? }
??????? if ( total < each )
??????? {
??????????? start = 0;
??????????? end = total;
??????? }
??????? else
??????? {
??????????? start = 0;
??????????? end = each;
??????? }
??? }
???
??? public int getCurrent()
??? {
??????? return current;
??? }
??? public void setCurrent( int current )
??? {
??????? this.current = current;
??? }
??? public int getEach()
??? {
??????? return each;
??? }
??? public void setEach( int each )
??? {
??????? this.each = each;
??? }
??? public boolean isNext()
??? {
??????? return next;
??? }
??? public void setNext( boolean next )
??? {
??????? this.next = next;
??? }
??? public boolean isPrevious()
??? {
??????? return previous;
??? }
??? public void setPrevious( boolean previous )
??? {
??????? this.previous = previous;
??? }
??? public int getEnd()
??? {
??????? return end;
??? }
??? public int getPages()
??? {
??????? return pages;
??? }
??? public int getStart()
??? {
??????? return start;
??? }
??? public int getTotal()
??? {
??????? return total;
??? }
?//獲取下一頁的對象們??
public Vector<E> getNextPage()
??? {
??????? current = current + 1;
??????? if ( (current - 1) > 0 )
??????? {
??????????? previous = true;
??????? }
??????? else
??????? {
??????????? previous = false;
??????? }
??????? if ( current >= pages )
??????? {
??????????? next = false;
??????? }
??????? else
??????? {
??????????? next = true;
??????? }
??????? Vector<E> os = gets();
??????? return os;
??? }
?//獲取上一頁
??? public Vector<E> getPreviouspage()
??? {
??????? current = current - 1;
??????? if ( current == 0 )
??????? {
??????????? current = 1;
??????? }
??????? if ( current >= pages )
??????? {
??????????? next = false;
??????? }
??????? else
??????? {
??????????? next = true;
??????? }
??????? if ( (current - 1) > 0 )
??????? {
??????????? previous = true;
??????? }
??????? else
??????? {
??????????? previous = false;
??????? }
??????? Vector<E> os = gets();
??????? return os;
??? }
?//一開始獲取的
??? public Vector<E> gets()
??? {
??????? if ( current * each < total )
??????? {
??????????? end = current * each;
??????????? start = end - each;
??????? }
??????? else
??????? {
??????????? end = total;
??????????? start = each * (pages - 1);
??????? }
??????? Vector<E> gets = new Vector<E>();
??????? for ( int i = start; i < end; i++ )
??????? {
??????????? E o = v.get( i );
??????????? gets.add( o );
??????? }
??????? return gets;
??? }
}
?而對于按不同搜索，我們需要一個FormBean，一般的搜索，都是模糊搜索，搜索個大概，而且輸入的信息中文的比重也會很大，所以，我把對中文字符的轉換放到了這個BEAN里，在進行select * from * where like這樣的查詢時，如果是like ''這樣就可以得到所有的記錄了，我便用這個來對付沒有輸入查詢關鍵字的情況，而like '%*%'可以匹配關鍵字，而%%也在這里添加上了！
package com.boya.subject.view;
import java.io.UnsupportedEncodingException;
import javax.servlet.http.HttpServletRequest;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionMapping;
public class SearchForm extends ActionForm
{
??? private static final long serialVersionUID = 1L;
??? private String key;
??? private String from;
??? public String getFrom()
??? {
??????? return from;
??? }
??? public void setFrom( String from )
??? {
??????? this.from = from;
??? }
???
? public void reset( ActionMapping mapping, HttpServletRequest req )
??? {
??????? this.key = null;
??? }
??? public String getKey()
??? {
??????? return key;
??? }
??? public void setKey( String key )
??? {
??????? try
??????? {
??????????? key = new String( key.getBytes( "iso-8859-1" ), "gb2312" );
??????? }
??????? catch ( UnsupportedEncodingException e )
??????? {
??????????? e.printStackTrace();
??????? }
??????? this.key = "%" + key + "%";
??? }
???
??? public String getAny(){
??????? return "%%";
??? }
}
前期都做好了，我現在就要開始訪問這個Action了，可是這個控制器還沒寫呢！這里是代碼
public class AdminUserAction extends AdminAction
{
??? private Vector<Student> ss; //用來裝結果的容器
??? private Page<Student> ps;
//分頁顯示的PAGE對象
??? protected ActionForward executeAction( ActionMapping mapping,
??????????? ActionForm form, HttpServletRequest req, HttpServletResponse res )
??????????? throws Exception
??? {
??????? if ( !isSupper( req ) )
??????? {
??????????? return notSupper( res );//如果不是超級管理員怎么辦？
??????? }
??????? Service service = getService();//獲取業務邏輯
??????? SearchForm sf = (SearchForm) form;//獲取搜索FORM
??????? String op = req.getParameter( "op" );//獲取用戶對頁面的操作
??????? String search = req.getParameter( "search" );//是否執行了搜索
??????? Vector<Student> temp = null;?//用于存放臨時反饋給用戶的結果容器
??????????????? if ( op == null )//如果用戶沒有執行上/下一頁的操作
??????????????? {
??????????????????? if ( search != null )//用戶如果執行了搜索
??????????????????? {
??????????????????????? if ( sf.getFrom().equalsIgnoreCase( "class" ) )//如果是按班級查找
??????????????????????? {
??????????????????????????? ss = service.getAllStudentBySchoolClassForAdmin( sf
??????????????????????????????????? .getKey() );//獲取from的關鍵字
??????????????????????? }
??????????????????????? else if ( sf.getFrom().equalsIgnoreCase( "name" ) )//如果是按姓名查找
??????????????????????? {
??????????????????????????? ss = service.getAllStudentByNameForAdmin( sf
??????????????????????????????????? .getKey() );
??????????????????????? }
??????????????????????? else if ( sf.getFrom().equalsIgnoreCase( "user" ) )//如果是按用戶名查找
??????????????????????? {
??????????????????????????? ss = service.getAllStudentByUserForAdmin( sf
??????????????????????????????????? .getKey() );
??????????????????????? }
??????????????????????? else
??????????????????????? {
??????????????????????????? ss = service.getAllStudentBySnForAdmin( sf.getKey() );//按學號查找
??????????????????????? }
??????????????????????? form.reset( mapping, req );//重置搜索表單
??????????????????? }
??????????????????? else
??????????????????? {
??????????????????????? ss = service.getAllStudentForAdmin( sf.getAny() ); //用戶未執行查找就顯示全部，
??????????????????? }
??????????????????? if ( ss != null && ss.size() != 0 )//如果查找不為空，有記錄，那就創建一個分頁對象
??????????????????? {
??????????????????????? ps = new Page<Student>( ss, 10 );//將查詢結果和每頁顯示記錄數作為參數構件對象
??????????????????????? temp = ps.gets();//并獲取第一頁
??????????????????? }
??????????????? }
??????????????? else//如果用戶執行了操作
??????????????? {
??????????????????? if ( op.equals( "next" ) )//操作是下一頁
??????????????????? {
??????????????????????? temp = ps.getNextPage();
??????????????????? }
??????????????????? if ( op.equals( "previous" ) )//操作是上一頁
??????????????????? {
??????????????????????? temp = ps.getPreviouspage();
??????????????????? }
??????????????? }
??????????????? req.setAttribute( "search", SelectUtil.studentSearch() );//把搜索用到的表單放到request中
??????????????? req.setAttribute( "students", temp );//該頁顯示的學生
??????????????? req.setAttribute( "page", ps );//分頁對象
??????????????? return mapping.findForward( "student" );//請求轉發
??? }
}
用到SelectUtil中的代碼如下：
/**
???? * 獲取學生查找類別的select
???? * @return 學生查找類別
???? * 2006-5-17 9:06:12
???? */
??? public static Vector<LabelValueBean> studentSearch()
??? {
??????? Vector<LabelValueBean> s = new Vector<LabelValueBean>();
??????? s.add( new LabelValueBean( "按學號查找", "sn" ) );
??????? s.add( new LabelValueBean( "按班級查找", "class" ) );
??????? s.add( new LabelValueBean( "按姓名查找", "name" ) );
??????? s.add( new LabelValueBean( "按用戶查找", "user" ) );
??????? return s;
??? }
在看頁面視圖前先讓我們看看Model吧，
public class Student extends User
{
??? private String sn;
??? private SchoolClass schoolClass;
//這里的班級做為了一種對象，我們在視圖顯示的時候就有了一層嵌套
??? public SchoolClass getSchoolClass()
??? {
??????? return schoolClass;
??? }
??? public void setSchoolClass( SchoolClass schoolClass )
??? {
??????? this.schoolClass = schoolClass;
??? }
??? public String getSn()
??? {
??????? return sn;
??? }
??? public void setSn( String sn )
??? {
??????? this.sn = sn;
??? }
??? public String getType()
??? {
??????? return "student";
??? }
}
在了解了model后，還是看看視圖吧，
先放個查詢表單：
<html:javascript dynamicJavascript="true" staticJavascript="true" formName="SearchForm" />
<html:form action="/adminUser.do?search=true" onsubmit="return validateSearchForm(this)">
<html:select property="from" >
<html:options collection="search" property="value" labelProperty="label" />
</html:select>
<html:text property="key" size="16" maxlength="16"/>
<html:image src="images/search.gif"/>
</html:form>
由于模型中有嵌套，那么我們就將用到Nested標簽，其實沒有嵌套也可以使用這個標簽，下面的是用于顯示信息的，用迭迨器進行遍歷request范圍的students，你不安排范圍，他會自動找到的，并把每次遍歷的對象起名叫student，并作為層次的根元素，
<logic:iterate id="student" name="students">
<nested:root name="student">
<nested:nest property="schoolClass"><nested:write property="schoolClass"/></nested:nest>//尋找了student的schoolClass屬性對象的schoolClass嵌套
<nested:write property="name"/>????? //student的名字
<nested:link page="/adminActions.do?method=deleteStudent" paramId="id" paramProperty="id" onclick="return window.confirm('您真的要刪除嗎？')">刪除</nested:link>
</nested:root>
這里是顯示分頁對象的：
第<bean:write name="page" property="current" />頁
共<bean:write name="page" property="pages" />頁
??????? //上一頁是否存在
????????<logic:equal name="page" property="previous" value="true">
???????????????<html:link page="/adminUser.do?part=student&op=previous">
????????????????<font color="6795b4">上一頁</font>
???????????????</html:link> ?
??????? </logic:equal>
????????<logic:notEqual name="page" property="previous" value="true">上一頁 ? </logic:notEqual>
????????
?????? //下一頁是否存在
?????????<logic:equal name="page" property="next" value="true">
?????????<html:link page="/adminUser.do?part=student&op=next">
??????????<font color="6795b4">下一頁</font>
?????????</html:link> ? </logic:equal>
????????<logic:notEqual name="page" property="next" value="true">下一頁 ? </logic:notEqual>
????????
共有<bean:write name="page" property="total" />條數據
</logic:iterate>
到這里不知道您看明白了多少，在我的這個JSP頁里幾乎沒有任何的業務邏輯，這樣的設計就比把HTML和JAVA攙雜在一起好了很多。