目录
1.准备工作
1.数据库源（这里以Mysql为例）
2.映射实体类
3.模拟三层架构（Dao、Service、Controller）
Dao接口
Dao实现
Service实现（这里省略Service接口）
Controller层（或叫Servlet层）
web.xml中注册该Servket
1.准备工作
1.数据库源（这里以Mysql为例）
<!-- 数据库依赖-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>因为是Servlet项目，所以要用到JDBC去连接后台数据库，此处还不熟悉的可借鉴我前几篇有关JDBC的文章
这里直接给出工具类JdbcUtil2：
public class JdbcUtil2 {
private static String url;
private static String username;
private static String password;
private static String driver;
static {
InputStream is = JdbcUtil2.class.getClassLoader().getResourceAsStream("db.properties");
Properties pro = new Properties();
try {
pro.load(is);
} catch (IOException e) {
throw new RuntimeException(e);
}
url = pro.getProperty("url");
username = pro.getProperty("username");
password = pro.getProperty("password");
driver = pro.getProperty("driver");
}
public static Connection getConnection() throws SQLException, ClassNotFoundException {
Class.forName(driver); // 显示加载驱动
return (Connection) DriverManager.getConnection(url,username,password); // 拿到连接
}
public static Statement getStatement(Connection connection) throws SQLException {
Statement statement = connection.createStatement();
return statement;
}
public static ResultSet getResultSet(Statement statement) throws SQLException {
ResultSet resultSet = statement.executeQuery("select * from book");
return resultSet;
}
public static void close(Connection connection,Statement statement,ResultSet resultSet) throws SQLException {
if(resultSet!=null){
resultSet.close();
resultSet = null;
}
if(statement!=null){
statement.close();
statement = null;
}
if(connection!=null){
connection.close();
connection = null;
}
}
public static void main(String[] args) throws SQLException, ClassNotFoundException {
Connection connection = JdbcUtil2.getConnection();
Statement statement = JdbcUtil2.getStatement(connection);
ResultSet resultSet = JdbcUtil2.getResultSet(statement);
while(resultSet.next()){
int id = resultSet.getInt("id");
String name = resultSet.getString("name");
double price = resultSet.getDouble("price");
System.out.println("id="+id+",name="+name+",price="+price);
}
JdbcUtil2.close(connection,statement,resultSet);
}
｝2.映射实体类
（这里我对应的数据库表是Book，所以创建实体类Book）
（这是简单的表设计，大家可直接模拟一个，或自行创建一个表，只要实体类对应上即可）
public class Book {
private int id;
private String name;
private double price;
public Book(int id, String name, double price) {
this.id = id;
this.name = name;
this.price = price;
}
public Book() {
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
@Override
public String toString() {
return "Book{" +
"id=" + id +
", name='" + name + '\'' +
", price=" + price +
'}';
}
}
3.模拟三层架构（Dao、Service、Controller）
Dao接口
public interface BookDao {
// 书本列表
public List<Book> bookList() throws SQLException, ClassNotFoundException;
}
Dao实现
public class BookDaoImpl implements BookDao {
// 书本列表
@Override
public List<Book> bookList() throws SQLException, ClassNotFoundException {
List<Book> books = new ArrayList<Book>();
Connection connection = JdbcUtil2.getConnection();
// 注意这里的JdbcUtil2是自己封装好的JDBC工具类
Statement statement = JdbcUtil2.getStatement(connection);
// 此处为了简便，不考虑sql注入，因此直接用statement而非prestatement
ResultSet resultSet = JdbcUtil2.getResultSet(statement);
// 获取结果集
while(resultSet.next()){
// 循环拿到每本书的信息，并存在每个新创建的book对象中
Book book = new Book();
book.setId(resultSet.getInt("id"));
book.setName(resultSet.getString("name"));
book.setPrice(resultSet.getDouble("price"));
books.add(book);// 添加每本书本信息在集合
}
return books; // 返回该集合
}
}Service实现（这里省略Service接口）
public class BookService {
public List<Book> getAllbooks() throws SQLException, ClassNotFoundException {
BookDao bookDao = new BookDaoImpl();
return bookDao.bookList();
}
｝Controller层（或叫Servlet层）
public class BookServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
List<Book> books = new ArrayList<Book>();
BookService bookService = new BookService();
try {
books = bookService.getAllbooks();// 调用Service层，拿到books集合
Gson gson = new GsonBuilder().create();
// 转换为json
String json = gson.toJson(books);
// 设置响应类型，指定为json
resp.setContentType("application/json");
// 指定字符集
resp.setCharacterEncoding("UTF-8");
// 返回数据
resp.getWriter().write(json);
} catch (SQLException e) {
throw new RuntimeException(e);
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}
web.xml中注册该Servket
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<!--设置首页-->
<welcome-file-list>
<welcome-file>Content.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>BookServket</servlet-name>
<servlet-class>zhan.controller.BookServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>BookServket</servlet-name>
<url-pattern>/BookServlet</url-pattern>
</servlet-mapping>
</web-app>
编写Content.jsp（html+js+ajax）
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>首页</title>
</head>
<body>
<h3>列表展示</h3>
<button id="listButton">
书本信息列表
</button>
<div id="bookList"></div>
<%--该div用于列表展示--%>
</body>
<%--引入jquery，用于调用ajax--%>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<script>
$(function (){
$("#listButton").click(function (){
$.ajax({
url: "http://localhost:8080/BookServlet",
type: "GET",
success: function (response){ // 一般来说，response对响应体内容的封装，我们可以从中获取值
var bookList = $("#bookList");
bookList.empty(); // 清空列表
response.forEach(function(book) {
bookList.append("id:"+book.id+",name:"+book.name+",price"+book.price+"<br>");
// 在response响应中遍历获取到的列表，以book为单位，不断填充在bookList这个div中
});
},
error: function (xhr, status, error) {
alert("服务器异常！");
}
});
});
});
</script>
