jstack檢視JVM堆疊資訊
阿新 • • 發佈：2020-11-23
首先我們應該瞭解什麼是MVC：
MVC包含三個部分 ：
①View：由各種JSP頁面組成。
②Controller：由各種Servlet組成，Controller就是將View和Model來進行匹配，用什麼Model實現，呼叫哪個View來顯示。
③Model：由各種javabean組成，也是MVC的核心，
以下就是簡單的用MVC架構去實現一個JSP（View）+Servlet（Controller）+javabean（Model）實現MySql查詢功能的Demo。
建立Web Project
1.開啟MyEclipse -> File-> new -> Web Project 建立完後在src下建立包beans和ServletDB最後得到例如以下的檔案結構：
2.編寫beans
在beans包下建立兩個javabeans分別為DAL.java 和 DB.java
DB.java 注意MySqlusername和password是你本機MySql的 username和password與下面的程式碼可能不一樣須要改動。
package beans;
import java.sql.*;
public class DB {
static String driver = "com.mysql.jdbc.Driver";
static String url = "jdbc:mysql://127.0.0.1:3306/test";
static String user = "root";//連線時的username
static String password = "root";//連線時的密碼
static Connection aConnection;
public static Connection connectDB(){
try{
Class.forName(driver);
aConnection = DriverManager.getConnection(url,user,password);
if(aConnection.isClosed())
{
System.out.print("Succeeded!");
}
}catch(ClassNotFoundException e){
System.out.println(e);
} catch (SQLException e) {
e.printStackTrace();
}
return aConnection;
}
public static ResultSet executeQuery(String sqlx) throws SQLException{
connectDB();
ResultSet rs = null;
Statement stmt = aConnection.createStatement();
try {
rs = stmt.executeQuery(sqlx);
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
}
DAL.java
package beans;
import java.sql.ResultSet;
import java.sql.SQLException;
public class DAL {
public static String sqlx="";
public static String testQueryByID(String ID){
ResultSet rs = null;
String result = "";
sqlx = "SELECT * FROM testtable where ID = '"+ID+"'";
try {
rs = DB.executeQuery(sqlx);
} catch (SQLException e) {
e.printStackTrace();
}
try {
while(rs.next()){
result = result +"ID:"+rs.getString("ID")+" Name:"+rs.getString("name")+"</br>";
}
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
}
3.編寫servlet
File-> new -> servlet->確定包名為servletDB然後取名為test即可了
重要的是在本test方法中增加呼叫beans方法的語句。
test.java
package servletDB;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import beans.DAL;
public class test extends HttpServlet {
/**
* Constructor of the object.
*/
public test() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
String ID = request.getParameter("ID");//獲取傳過來的ID
String result = "";
result = DAL.testQueryByID(ID);//呼叫DAL中的testQueryByID方法而且將get過來的ID傳過去
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(result);
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
public void init() throws ServletException {
// Put your code here
}
}
4.配置Servlet
進入WebRoot-〉Web-INF -〉web.xml加入例如以下程式碼
<servlet-name>test</servlet-name> <servlet-class>servletDB.test</servlet-class> </servlet> <servlet-mapping> <servlet-name>test</servlet-name> <url-pattern>/servletDB/test</url-pattern>
寫index.jsp
將body中的程式碼替換為例如以下程式碼
<form action="servletDB/test" method="get">
請輸入使用者ID：<input type="text" name="ID"><br>
<input type="submit" value="提交">
</form>
測試
1.點選Run
2.輸入測試ID 1
成功的獲取到了test資料庫testtable中ID為1的資料。
轉載於