JavaWeb三层架构详解

2024-07-18 00:10| 来源: 网络整理| 查看: 265

什么是三层架构？

三层架构(3-tier architecture) 通常意义上的三层架构就是将整个业务应用划分为：界面层（User Interface layer）、业务逻辑层（Business Logic Layer）、数据访问层（Data access layer）。区分层次的目的即为了“高内聚低耦合”的思想。在软件体系架构设计中，分层式结构是最常见，也是最重要的一种结构。微软推荐的分层式结构一般分为三层，从下至上分别为：数据访问层（又称为持久层）、业务逻辑层（又或称为领域层）、表示层。

表示层（UI层）:

表示层也称为界面层，位于最外层（最上层），离用户最近。用于显示数据和接收用户输入的数据，为用户提供一种交互式操作的界面。

业务逻辑层（BLL层）:

负责关键业务的处理和数据的传递。复杂的逻辑判断和涉及到数据库的数据验证都需要在此做出处理。主要是针对具体的问题的操作，也可以理解成对数据层的操作，对数据业务逻辑处理，如果说数据层是积木，那逻辑层就是对这些积木的搭建。

数据访问层（DAL层）：

主要负责对数据库的直接访问，为业务逻辑层提供数据，根据传入的值来操作数据库，增、删、改、查。

为什么要用三层架构呢？

1.团队开发，便于管理

三层架构使得合作开发成为可能，由于各层相互独立，一个小组只需负责一小块就可以。结构化的编程方法面对大型的项目会感到力不从心，因为结构化设计必定会使程序变的错综复杂。逻辑主要在BLL层，就使得UI层也就是客户端不承担太多的职责，即使更新业务逻辑，也无需修改客户端，不用重新部署。

2.解耦

上一层依赖于下一层，如果测试下一层没有问题，那么问题就只有可能发现在本层了，便于发现和改正BUG。体现了“高内聚，低耦合”的思想。比如楼房是分层的，我们要到哪一层楼非常方便，只需在电梯里按下那个楼层的层号即可。而三层架构就好比开发的软件“楼”，哪层出现Bug，哪层有问题，我们作为开发人员能够随时找到，并修正。各个层次分工明确，将一个复杂问题简单拆分了。

3.代码的复用和劳动成本的减少

分层的根本在于代码的复用和劳动成本的减少。分层的最理想化的结果是实现层与层之间的互不依赖的内部实现，所谓的即插即用！

当然啦，三层架构也是有一定的缺点，但是总的来说，利大于弊。

那么下面写一个小项目来具体地深入了解一下三层架构

项目目录如下:

表示层Model：

package com.gpnu.book.entity; public class Books { @Override public String toString() { return "Books [book_id=" + book_id + ", book_name=" + book_name + ", isbn=" + isbn + ", author=" + author + "]"; } public Books() { } public Books(int book_id, String book_name, String isbn, String author) { super(); this.book_id = book_id; this.book_name = book_name; this.isbn = isbn; this.author = author; } private int book_id; private String book_name; private String isbn; private String author; public int getBook_id() { return book_id; } public void setBook_id(int book_id) { this.book_id = book_id; } public String getBook_name() { return book_name; } public void setBook_name(String book_name) { this.book_name = book_name; } public String getIsbn() { return isbn; } public void setIsbn(String isbn) { this.isbn = isbn; } public String getAuthor() { return author; } public void setAuthor(String author) { this.author = author; } }

表示层Controller:

BooksServlet.java

package com.gpnu.book.servlet; import java.io.IOException; import java.util.List; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.gpnu.book.entity.Books; import com.gpnu.book.service.BooksService; import com.gpnu.book.service.impl.BooksServiceImpl; /** * Servlet implementation class Books */ @WebServlet("/BooksServlet") public class BooksServlet extends HttpServlet { private static final long serialVersionUID = 1L; BooksService booksService = BooksServiceImpl.getInstance(); /** * @see HttpServlet#HttpServlet() */ public BooksServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().append("Served at: ").append(request.getContextPath()); doPost(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String action = request.getParameter("action"); System.out.println("action:" + action); if (action.equals("add")) { doAddBooks(request, response); response.sendRedirect("index.jsp"); }else if (action.equals("select")) { response.sendRedirect(request.getContextPath() + "/Books/selBooks.jsp"); }else if (action.equals("remove")) { doDelBooks(request, response); response.sendRedirect("SelBooksServlet"); } } private void doAddBooks(HttpServletRequest request, HttpServletResponse response) throws IOException { Books book = new Books(); //book.setBook_id(Integer.parseInt(request.getParameter("book_id"))); book.setBook_name(request.getParameter("book_name")); book.setIsbn(request.getParameter("isbn")); book.setAuthor(request.getParameter("author")); int result = booksService.addBooks(book); if (result > 0) System.out.println("添加book成功"); else System.out.println("添加book失败"); } private void doDelBooks(HttpServletRequest request, HttpServletResponse response) throws IOException { int id = Integer.parseInt(request.getParameter("id")); int result = booksService.delBooks(id); if (result > 0) System.out.println("删除book成功"); else System.out.println("删除book失败"); } }

SelBooksServlet.java

package com.gpnu.book.servlet; import java.io.IOException; import java.util.ArrayList; import java.util.List; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.gpnu.book.entity.Books; import com.gpnu.book.service.BooksService; import com.gpnu.book.service.impl.BooksServiceImpl; /** * Servlet implementation class SelBooksServlet */ @WebServlet("/SelBooksServlet") public class SelBooksServlet extends HttpServlet { private static final long serialVersionUID = 1L; BooksService booksService = BooksServiceImpl.getInstance(); /** * @see HttpServlet#HttpServlet() */ public SelBooksServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().append("Served at: ").append(request.getContextPath()); doPost(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ private static String keyword = ""; protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); keyword = request.getParameter("keyword"); System.out.println("keyword:" + keyword); if (keyword == "") doSelAllBooks(request, response); else doSelBooks(request, response); } private void doSelAllBooks(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { List list = booksService.selAllBooks(); request.setAttribute("books", list); System.out.println("查询所有"); RequestDispatcher view = request.getRequestDispatcher("/Books/selResult.jsp"); view.forward(request, response); } private void doSelBooks(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { Books book = booksService.selBooks(keyword); List list = new ArrayList(); list.add(book); request.setAttribute("books", list); System.out.println("条件查询"); RequestDispatcher view = request.getRequestDispatcher("/Books/selResult.jsp"); view.forward(request, response); } }

表示层View:

index.jsp

Insert title here 添加查询

addBooks.jsp

Insert title here 图书名称: 国际标准书号: 作者:

selBooks.jsp

Insert title here

selResult.jsp

Insert title here 新增图书编号图书名称国际标准号作者

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