I'm trying to do simple web application. But i think, i configured it wrong. Here is my project structure:
Here is my Service class with connection to postgresql
package NedraTask;
import java.sql.*;
public class CounterService {
private final String url = "jdbc:postgresql://localhost/postgres";
private final String username = "postgres";
private final String password = "examplePassword";
private Connection connection;
CounterService() {
try {
connection = DriverManager.getConnection(url, username, password);
createIfNotExistsAndInsert(connection);
}catch (Exception ex) {}
}
/**
* creates table with name COUNTERS
* with 1 INTEGER column
* with name COUNTER
*/
private void createIfNotExistsAndInsert(Connection conn) throws SQLException {
conn.setAutoCommit(false);
DatabaseMetaData dbm = conn.getMetaData();
ResultSet rs = dbm.getTables(null, null, "COUNTERS", null);
if (!rs.next()) {
conn.createStatement().executeUpdate("create table if not exists COUNTERS(COUNTER INTEGER)");
conn.createStatement().executeUpdate("INSERT INTO COUNTERS VALUES 0");
}
conn.commit();
conn.setAutoCommit(true);
}
public int getCounter() throws SQLException{
ResultSet resultSet = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY)
.executeQuery("SELECT * FROM COUNTERS");
int currentCounter = 0;
while(resultSet.next())
currentCounter = resultSet.getInt(1);
return currentCounter;
}
public void incrCounter() throws SQLException {
PreparedStatement statement = connection.prepareStatement(
"UPDATE COUNTERS SET COUNTER = COUNTER + 1",
ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_UPDATABLE,
ResultSet.CLOSE_CURSORS_AT_COMMIT);
statement.executeUpdate();
}
}
Here is my Servlet class:
package NedraTask;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
public class CounterServlet extends javax.servlet.http.HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try{
CounterService cs = new CounterService();
request.setAttribute("count", Integer.toString(cs.getCounter()));
getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}catch(Exception ex){
request.setAttribute("count", "Some error at doPOST method");
getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try{
CounterService cs = new CounterService();
request.setAttribute("count", Integer.toString(cs.getCounter()));
getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}
catch(Exception ex){
request.setAttribute("count", "Some error at doGET method");
getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}
}
}
Here is my JSP class:
<%--@ page contentType="text/html;charset=UTF-8" language="java" --%>
<!DOCTYPE html>
<html>
<head>
<title>Title</title>
<style>
.button {
background-color: #4CAF50;
border: none;
color: white;
padding: 15px 32px;
text-align: center;
text-decoration: none;
display: inline-block;
font-size: 16px;
margin: 4px 2px;
cursor: pointer;
}
</style>
</head>
<body>
<p>Count: ${count}</p>
<button type="button" class="button" id="myBtn" onclick="myFunction()">Add</button>
<script>
function myFunction() {
var x = document.getElementById("myBtn");
var xhr = new XMLHttpRequest();
xhr.open("POST", '/task_war_exploded');
xhr.send();
}
</script>
</body>
</html>
I expected that it will return an html page with counter value (from DB), and with click button it will concurrent-safety add 1 to counter value in DB and returns new value.
But here server didnt replase ${count}:
Here is my configuration: 
I created web application from "add Framework support to project": 
My web.xml file:
<?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">
<servlet>
<servlet-name>CounterServlet</servlet-name>
<servlet-class>NedraTask.CounterServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CounterServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>
What did i wriong? Did i configured my application wrong, or wrong code? Run Output LOG INFO return some exceptions in catalina and tomcat at the start. Shall i post them?
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