我想在页面加载后访问数据，但它不起作用。似乎没有在jsp中调用getConnection函数，也没有调用响应Json。我不知道为什么它不起作用。我的代码有什么问题以及如何修复它？非常感谢你。
MyServlet.java
import java.io.*;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.reflect.TypeToken;
/**
* Servlet implementation class MyServlet
*/
public class MyServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public MyServlet() {
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
ArrayList<Dish> country=new ArrayList<Dish>();
country=SQLConnection.getAllDish();
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(country, new TypeToken<List<Dish>>() {}.getType());
JsonArray jsonArray = element.getAsJsonArray();
response.setContentType("application/json");
response.getWriter().print(jsonArray);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
SQLConnection.java
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.ArrayList;
import java.util.Properties;
public class SQLConnection {
// java.sql.Connection connection;
private static Connection connection = null;
static String url, driver, username, password;
public static Connection getConnection() {
if (connection != null)
return connection;
else {
try {
Properties prop = new Properties();
InputStream inputStream = SQLConnection.class.getClassLoader().getResourceAsStream("/db.properties");
prop.load(inputStream);
driver = prop.getProperty("driver");
url = prop.getProperty("url");
username = prop.getProperty("user");
password = prop.getProperty("password");
Class.forName(driver);
connection = DriverManager.getConnection(url, username, password);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return connection;
}
}
public static ArrayList<Dish> getAllDish() {
ArrayList<Dish> arrDish = null;
try {
//Creating a statement object
Statement stmt = connection.createStatement();
//Executing the query and getting the result set
ResultSet rs = stmt.executeQuery("select * from dish");
arrDish = new ArrayList<Dish>();
//Iterating the resultset and printing the 3rd column
while (rs.next()) {
Dish item = new Dish(rs.getInt(1), rs.getInt(2), rs.getString(3), rs.getDouble(4), rs.getString(5),
rs.getString(6), rs.getString(7), rs.getString(8), rs.getInt(9), rs.getInt(10), rs.getInt(11), rs.getInt(12));
arrDish.add(item);
}
//close the resultset, statement and connection.
rs.close();
stmt.close();
connection.close();
return arrDish;
} catch (SQLException e) {
e.printStackTrace();
}
return arrDish;
}
}
的hello.jsp
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<html>
<head>
<link rel="stylesheet" href="${pageContext.request.contextPath}/style.css" />
<title><fmt:message key="title" /></title>
</head>
<body bgcolor="#FEDDFF">
<script
src="//ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script type="text/javascript" src="js/slider.js"></script>
<script>
$(window).ready(function() {
$.get('MyServlet',function(responseJson) {
if(responseJson!=null){
$("#dishes").find("tr:gt(0)").remove();
var table1 = $("#dishes");
$.each(responseJson, function(key,value) {
var rowNew = $("<tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr>");
rowNew.children().eq(0).int(value['dishid']);
rowNew.children().eq(1).int(value['userid']);
rowNew.children().eq(2).text(value['dishName']);
rowNew.children().eq(3).double(value['numberOfPeople']);
rowNew.children().eq(4).text(value['dishImg']);
rowNew.children().eq(5).text(value['ingredient']);
rowNew.children().eq(6).text(value['step']);
rowNew.children().eq(7).text(value['descOfDish']);
rowNew.children().eq(8).int(value['category1']);
rowNew.children().eq(9).int(value['category2']);
rowNew.children().eq(10).int(value['category3']);
rowNew.children().eq(11).int(value['rate']);
rowNew.appendTo(table1);
});
}
});
});
</script>
<div id="tabledish">
<table cellspacing="0" id="dishes">
<tr>
<th scope="col">dishid</th>
<th scope="col">userid</th>
<th scope="col">dishName</th>
<th scope="col">numberOfPeople</th>
<th scope="col">dishImg</th>
<th scope="col">ingredient</th>
<th scope="col">step</th>
<th scope="col">descOfDish</th>
<th scope="col">category1</th>
<th scope="col">category2</th>
<th scope="col">category3</th>
<th scope="col">rate</th>
</tr>
</table>
</div>
</body>
答案 0 :(得分：0)
检查并调用getConnection（）;
try{
if(connection==null)
getConnection();
Statement stmt = connection.createStatement();
...