alex cintea

Hi! I've seen your issue with charAt() method and this is what you can do.

String s = "12345"; String varSubstring = s.substring(0,1); String varCharAt = Character.toString(s.charAt(0));

@Tsank Thanks for your explication!


So is it alright if I do something like that ?

It works alright with this modification but I would like to know if it is a reliable solution.

Thanks!

public static boolean eaterExists(String name) { connection = DatabaseConnection.getConnection(); PreparedStatement pstmt = null; ResultSet rs = null; try { String query = "SELECT name FROM eaters WHERE name = ?;"; pstmt = connection.prepareStatement(query); pstmt.setString(1, name); rs = pstmt.executeQuery(); if(rs.next()) { return true; } else { return false; } } catch(SQLException e) { e.printStackTrace(); } finally { DatabaseConnection.closeConnection(); } return false; }

K. Tsang wrote:The error says it all, the connection is already closed when you try to insert data.

How is your code set up?

Method selectEaters()
public static void selectEaters() throws SQLException { DatabaseConnection.getConnection(); try { Statement stmt = connection.createStatement(); String query = "SELECT id,name, email FROM eaters"; ResultSet rs = stmt.executeQuery(query); while(rs.next()){ int id = rs.getInt("ID"); String name = rs.getString("name"); String email = rs.getString("email"); System.out.println("ID:" + id + " Name: " + name + " Email: " + email); } } catch(SQLException e) { e.printStackTrace(); } finally { DatabaseConnection.closeConnection(); } }

Method insertEaterDB()
public static void insertEaterDB(String name, String email, String password, String rpassword) { DatabaseConnection.getConnection(); PreparedStatement pstmt = null; try { String qry = "INSERT INTO eaters (name, email, password, rpassword) VALUES (?,?,?,?);"; pstmt = connection.prepareStatement(qry); pstmt.setString(1, name); pstmt.setString(2, email); pstmt.setString(3, password); pstmt.setString(4, rpassword); pstmt.executeUpdate(); } catch(SQLException e){ e.printStackTrace(); } finally { DatabaseConnection.closeConnection(); } }

DatabaseConnection.java
package com.eb; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; public class DatabaseConnection { private static Connection connection = null; private static DatabaseConnection instance = null; private final static String ADDRESS = "jdbc:postgresql://localhost"; private final static String USERNAME = "postgres"; private final static String DATABASE = "postgres"; private final static String PASSWORD = "Naicum414"; private final static String PORT = "5432"; private final static String DRIVER = "org.postgresql.Driver"; //constructor private DatabaseConnection() { } public static DatabaseConnection getInstance() { if(instance == null) { instance = new DatabaseConnection(); } return instance; } public static Connection loadDriver() { try { Class.forName(DRIVER); } catch (Exception e) { System.out.println("Failed to load the driver: " + e); } return connection; } private static String getFormatedUrl() { return ADDRESS + ":" + PORT + "/" + DATABASE; } private static void loadConnection() { try { connection = DriverManager.getConnection(getFormatedUrl(), USERNAME, PASSWORD); } catch(SQLException e) { System.out.println("Failed to connect to the database: " + getFormatedUrl() + e); } } public static Connection getConnection() { if(connection == null) { loadDriver(); loadConnection(); } return connection; } public static void closeConnection() { if(connection == null) { System.err.println("No connection found"); } else { try { connection.close(); connection = null; } catch(SQLException e) { System.err.println("Failed to close the connection:" + e); } } } }

I have an application that crashes after my first attempt to insert a record in PostgreSQL. Everything works Ok, but if I want to insert another record my program crashes.

I don't have any SELECT * within my queries. Any help will be appreciated.

That's the error I receive :

org.postgresql.util.PSQLException: This connection has been closed. at org.postgresql.jdbc2.AbstractJdbc2Connection.checkClosed(AbstractJdbc2Connection.java:843) at org.postgresql.jdbc3.AbstractJdbc3Connection.prepareStatement(AbstractJdbc3Connection.java:275) at org.postgresql.jdbc2.AbstractJdbc2Connection.prepareStatement(AbstractJdbc2Connection.java:317) at com.eb.DBManager.emailExists(DBManager.java:106) at servlet.CreateAccountServlet.doPost(CreateAccountServlet.java:32) at javax.servlet.http.HttpServlet.service(HttpServlet.java:637) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source) org.postgresql.util.PSQLException: This connection has been closed. at org.postgresql.jdbc2.AbstractJdbc2Connection.checkClosed(AbstractJdbc2Connection.java:843) at org.postgresql.jdbc3.AbstractJdbc3Connection.prepareStatement(AbstractJdbc3Connection.java:275) at org.postgresql.jdbc2.AbstractJdbc2Connection.prepareStatement(AbstractJdbc2Connection.java:317) at com.eb.DBManager.insertEaterDB(DBManager.java:37) at servlet.CreateAccountServlet.doPost(CreateAccountServlet.java:40) at javax.servlet.http.HttpServlet.service(HttpServlet.java:637) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source)

@Ivan Krasic First of all, I would like to thank you for your reply to my post and for your solution. I've seen the error after I pressed on Submit button. That was the error and hope that from now on to be more careful on what I do

Cheers!

Hi all!
I've just started to work with Struts and I get the following error:

Struts has detected an unhandled exception:

Messages:
No result defined for action com.tutorialspoint.struts2.HelloWorldAction and result Success

web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> <display-name>HelloWorldStrut2</display-name> <display-name>Struts 2</display-name> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>struts2</filter-name> <filter-class> org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter </filter-class> </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app>

struts.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"> <struts> <constant name="struts.devMode" value="true" /> <package name="helloworld" extends="struts-default" namespace="/"> <action name="hello" class="com.tutorialspoint.struts2.HelloWorldAction" method="execute"> <result name="success">/HelloWorld.jsp</result> </action> </package> </struts>

index.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib prefix="s" uri="/struts-tags"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <title>Hello World</title> </head> <body> <h1>Hello World From Struts2</h1> <form action="hello"> <label for="name">Please enter your name</label><br/> <input type="text" name="name"/> <input type="submit" value="Say Hello"/> </form> </body> </html>

HelloWorld.jsp
<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib prefix="s" uri="/struts-tags" %> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Hello World</title> </head> <body> Hello World, <s:property value="name"/> </body> </html>


HelloWorldAction.java
package com.tutorialspoint.struts2; public class HelloWorldAction { private String name; public String execute() throws Exception { return "Success"; } public String getName() { return name; } public void setName(String name) { this.name = name; } }

It doesn't appear anything because you just compile the java file. A .class file has been created for you and now remains to run the command [java filename]
Compiling a java file: javac fileName.java Running java filename

Hi everyone!

I want to get certified on Java programming but I find it very difficult what certification to choose from. Could you please tell me what certification to choose from? SCJP, OCA.

Thanks for taking the time

int i1 = -123;
System.out.printf(">%1$(7d< \n", i1);

printf("format string", argument(s));
%[arg_index$][flags][width][.precision]conversion char

The formatting data always start with the % sign.

1$ - represents the first argument that should be printed

() - enclose negative numbers in parentheses

7d - means that the string will have the width of 7 integers

\n - escape character new line


Hope that this will help you.