CRUD是Create(创建)、Read(读取)、Update(更新)和Delete(删除)的缩写,它是普通应用程序的缩影。如果您掌握了某框架的CRUD编写,那么意味可以使用该框架创建普通应用程序了,所以大家使用新框架开发OLTP(Online Transaction Processing)应用程序时,首先会研究一下如何编写CRUD。这类似于大家在学习新编程语言时喜欢编写“Hello World”。
本文旨在讲述Struts 2上的CRUD开发,所以为了例子的简单易懂,我不会花时间在数据库的操作上。取而代之的是一个模拟数据库的哈希表(Hash Map)。
首先,让我们看看的“冒牌”的DAO(Data Access Object,数据访问对象),代码如下:
package tutorial.dao; import java.util.Collection; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import tutorial.model.Book; public class BookDao { private static final BookDao instance; private static final ConcurrentMap<String, Book> data; static { instance = new BookDao(); data = new ConcurrentHashMap<String, Book>(); data.put("978-0735619678", new Book("978-0735619678", "Code Complete, Second Edition", 32.99)); data.put("978-0596007867", new Book("978-0596007867", "The Art of Project Management", 35.96)); data.put("978-0201633610", new Book("978-0201633610", "Design Patterns: Elements of Reusable Object-Oriented Software", 43.19)); data.put("978-0596527341", new Book("978-0596527341", "Information Architecture for the World Wide Web: Designing Large-Scale Web Sites", 25.19)); data.put("978-0735605350", new Book("978-0735605350", "Software Estimation: Demystifying the Black Art", 25.19)); } private BookDao() {} public static BookDao getInstance() { return instance; } public Collection<Book> getBooks() { return data.values(); } public Book getBook(String isbn) { return data.get(isbn); } public void storeBook(Book book) { data.put(book.getIsbn(), book); } public void removeBook(String isbn) { data.remove(isbn); } public void removeBooks(String[] isbns) { for(String isbn : isbns) { data.remove(isbn); } }}清单1 src/tutorial/dao/BookDao.java
以上代码相信不用解释大家也清楚,我使用ConcurrentMap数据结构存储Book对象,这主要是为了方便检索和保存Book对象;另外,我还将data变量设为静态唯一来模拟应用程序的数据库。
接下来是的数据模型Book类,代码如下:
package tutorial.model; public class Book { private String isbn; private String title; private double price; public Book() { } public Book(String isbn, String title, double price) { this.isbn = isbn; this.title = title; this.price = price; } public String getIsbn() { return isbn; } public void setIsbn(String isbn) { this.isbn = isbn; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } }清单2 src/tutorial/model/Book.java
Book类有三个属性isbn,、title和price分别代表书籍的编号、名称和价格,其中编号用于唯一标识书籍(相当数据库中的主键)。
然后,我们再来看看Action类的代码:
package tutorial.action; import java.util.Collection; import tutorial.dao.BookDao; import tutorial.model.Book; import com.opensymphony.xwork2.ActionSupport; public class BookAction extends ActionSupport { private static final long serialVersionUID = 872316812305356L; private String isbn; private String[] isbns; private Book book; private Collection<Book> books; private BookDao dao = BookDao.getInstance(); public Book getBook() { return book; } public void setBook(Book book) { this.book = book; } public String getIsbn() { return isbn; } public void setIsbn(String isbn) { this.isbn = isbn; } public String[] getIsbns() { return isbns; } public void setIsbns(String[] isbns) { this.isbns = isbns; } public Collection<Book> getBooks() { return books; } public void setBooks(Collection<Book> books) { this.books = books; } public String load() { book = dao.getBook(isbn); return SUCCESS; } public String list() { books = dao.getBooks(); return SUCCESS; } public String store() { dao.storeBook(book); return SUCCESS; } public String remove() { if(null != isbn) { dao.removeBook(isbn); } else { dao.removeBooks(isbns); } return SUCCESS; }}清单3 src/tutorial/action/BookAction.java
BookAction类中属性isbn用于表示待编辑或删除的书籍的编号,属性isbns用于表示多个待删除的书籍的编号数组,属性book表示当前书籍,属性books则表示当前的书籍列表。BookAction有四个Action方法分别是load、list、store和remove,也即是CRUD都集中在BookAction中实现。
再下来是Action的配置代码:
<? xml version="1.0" encoding="UTF-8" ?> <! DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd" > < struts > < package name ="Struts2_CRUD_DEMO" extends ="struts-default" namespace ="/Book" > < action name ="List" class ="tutorial.action.BookAction" method ="list" > < result > List.jsp </ result > </ action > < action name ="Edit" class ="tutorial.action.BookAction" method ="load" > < result > Edit.jsp </ result > </ action > < action name ="Store" class ="tutorial.action.BookAction" method ="store" > < result type ="redirect" > List.action </ result > </ action > < action name ="Remove" class ="tutorial.action.BookAction" method ="remove" > < result type ="redirect" > List.action </ result > </ action > </ package > </ struts >清单4 src/struts.xml
以上的配置中,我使用了四个Action定义。它们都在“/Book”名值空间内。这样我就可以分别通过“http://localhost:8080/Struts2_CRUD/Book/List.action”、“http://localhost:8080/Struts2_CRUD/Book/Edit.action”、“http://localhost:8080/Struts2_CRUD/Book/Store.action”和“http://localhost:8080/Struts2_CRUD/Book/Remove.action”来调用BookAction的四个Action方法进行CRUD操作。当然,这只是个人喜好,你大可以只定义一个Action(假设其名称为“Book”),之后通过“http://localhost:8080/Struts2_CRUD/Book!list.action”的方式来访问,详细做法请参考《Struts 2.0的Action讲解》。另外,我由于希望在完成编辑或删除之后回到列表页,所以使用类型为redirect(重定向)的result。
下面是列表页面的代码:
<% @ page language = " java " contentType = " text/html; charset=utf-8 " pageEncoding = " utf-8 " %> <% @ taglib prefix = " s " uri = " /struts-tags " %> <! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > < html xmlns ="http://www.w3.org/1999/xhtml" > < head > < title > Book List </ title > < style type ="text/css" > table { border : 1px solid black ; border-collapse : collapse ; } table thead tr th { border : 1px solid black ; padding : 3px ; background-color : #cccccc ; } table tbody tr td { border : 1px solid black ; padding : 3px ; } </ style > </ head > < body > < h2 > Book List </ h2 > < s:form action ="Remove" theme ="simple" > < table cellspacing ="0" > < thead > < tr > < th > Select </ th > < th > ISBN </ th > < th > Title </ th > < th > Price </ th > < th > Operation </ th > </ tr > </ thead > < tbody > < s:iterator value ="books" > < tr > < td >< input type ="checkbox" name ="isbns" value ='<s:property value ="isbn" /> ' /> </ td > < td >< s:property value ="isbn" /></ td > < td >< s:property value ="title" /></ td > < td > $ < s:property value ="price" /></ td > < td > < a href ='<s:url action ="Edit" >< s:param name ="isbn" value ="isbn" /></ s:url > '> Edit </ a > < a href ='<s:url action ="Remove" >< s:param name ="isbn" value ="isbn" /></ s:url > '> Delete </ a > </ td > </ tr > </ s:iterator > </ tbody > </ table > < s:submit value ="Remove" />< a href ="Edit.jsp" > Add Book </ a > </ s:form > </ body > </ html >清单5 WebContent/Book/List.jsp
以上代码,值得注意的是在<s:form>标签,我设置了theme属性为“simple”,这样可以取消其默认的表格布局。之前,有些朋友问我“如果不希望提交按钮放在右边应该怎样做?”,上述做汗是答案之一。当然,更佳的做法自定义一个theme,并将其设为默认应用到整个站点,如此一来就可以得到统一的站点风格。我会在以后的文章中会对此作详细的描述。
编辑或添加书籍的页面代码如下:
<% @ page language = " java " contentType = " text/html; charset=utf-8 " pageEncoding = " utf-8 " %> <% @ taglib prefix = " s " uri = " /struts-tags " %> <! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > < html xmlns ="http://www.w3.org/1999/xhtml" > < head > < title > Book </ title > </ head > < body > < h2 > < s:if test ="null == book" > Add Book </ s:if > < s:else > Edit Book </ s:else > </ h2 > < s:form action ="Store" > < s:textfield name ="book.isbn" label ="ISBN" /> < s:textfield name ="book.title" label ="Title" /> < s:textfield name ="book.price" label ="Price" /> < s:submit /> </ s:form > </ body > </ html >清单6 WebContent/Book/Edit.jsp
如果book为null,则表明该页面用于添加书籍,反之则为编辑页面。
为了方便大家运行示例,我把web.xml的代码也贴出来,如下:
<? xml version="1.0" encoding="UTF-8" ?> < web-app id ="WebApp_9" version ="2.4" xmlns ="http://java.sun.com/xml/ns/j2ee" xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation ="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" > < display-name > Struts 2 Fileupload </ display-name > < filter > < filter-name > struts2 </ filter-name > < filter-class > org.apache.struts2.dispatcher.FilterDispatcher </ filter-class > </ filter > < filter-mapping > < filter-name > struts2 </ filter-name > < url-pattern > /* </ url-pattern > </ filter-mapping > < welcome-file-list > < welcome-file > index.html </ welcome-file > </ welcome-file-list > </ web-app >清单7 WebContent/WEB-INF/web.xml
大功告成,下面发布运行应用程序,在浏览器中键入:http://localhost:8080/Struts2_CRUD/Book/List.action,出现如下图所示页面:
清单8 列表页面
点击“Add Book”,出现如下图所示页面:
清单9 添加书籍页面
后退回到列表页面,点击“Edit”,出现如下图所示页面:
清单10 编辑书籍页面
本文只是粗略地了介绍Struts 2的CRUD实现方法,所以有很多功能没有实现,如国际化和数据校验等。大家可以在上面例子的基础将其完善,当作练习也不错。如果过程中有不明白之处,可以参考我早前的文章或给我发E-Mail:max.m.yuan@gmail.com。
转自:http://www.blogjava.net/max/archive/2007/04/13/110310.html