I write a code in servlet for login checking I don't know why I get an error like java.sql.SQLException: No data found, if I had not commented out the String s4 = rs.getString(1) and out.println(s4) line if I commented out this lines I did not get any error.
Why do I get an error like this? I cannot find out the answer.
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class login extends HttpServlet {
Connection conn;
Statement stmt;
ResultSet rs;
String s = "";
public void init() {
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
conn = DriverManager.getConnection("Jdbc:Odbc:edsn");
s = "Your information is connected ......";
} catch (Exception e) {
s = "Exception 1....." + e.getMessage();
}
}
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws IOException, ServletException {
res.setContentType("text/html;charset=UTF-8");
PrintWriter out = res.getWriter();
out.println(s);
try {
String ID = req.getParameter("T1");
String query = "select * from user_db ";
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
out.println("user" + " " + "pass");
while (rs.next()) {
try {
if ((rs.getString(1)).equals(ID)) {
String s4 = rs.getString(1);
out.println(s4);
out.println("<html><body><h> login Pass.....:(</h></body></html>");
}
} catch (Exception e) {
out.println(e);
}
}
} catch (Exception e) {
out.println("Unable To Show the info... . . ." + e.getMessage());
}
}
}
Why write the code like this ? It's very wasteful going over the whole table...
The IO alone...
Why not change to this:
ResultSet rs = null;
PreparedStatement st = null;
try {...
String ID = req.getParameter("T1");
String query = "select 1 from user_db where col_name = ?";
st = conn.prepareStatement(query);
st.setString(1, ID);
rs = st.executeQuery();
if (rs.next()) {
out.println(ID);
out.println("<html><body><h> login Pass.....:(</h></body></html>");
}
..
} finally {
if (rs != null) try { rs.close();}catch (Exception e) {}
if (st != null) try { st.close();}catch (Exception e) {}
}
notice prepared statements are cached and better for frequent use
you let the db do what its good at - search the data
select 1 instead of select * does not bring back data you dont really need
jdbc works harder the more columns and data in general you return, so only get what you
need
and add a finally block to always close your db connections properly
Calling methods on Connection, Statement, or ResultSet depend on which JDBC driver you've loaded. All the values of the ResultSet could be set as soon as the query is made, or they could be retrieved from the database as they're needed, depending on the implementation of the driver.
The JdbcOdbcDriver throws an SQLException after calling getString for a second time. This can be worked around be storing the values in Strings instead of making multiple calls, or by switching to a different driver.
Related
I'm having a problem with my derby engine.
When I make a new database , create new tables and insert or display rows , everything works fine. And when I try to use the database in my practice example , the database works fine and I'm able to insert and select data from the table.
Code:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSetMetaData;
public class Restaurants
{
private static String dbURL = "jdbc:derby:c:\\Apache\\db-derby-10.14.2.0-bin\\bin\\myDBExample;create=true";
private static String tableName = "restaurants";
// jdbc Connection
private static Connection conn = null;
private static Statement stmt = null;
public static void main(String[] args)
{
createConnection();
//insertRestaurants(5, "LaVals Leb", "Berkeley");
//insertRestaurants(6, "House Leb", "New York");
selectRestaurants();
shutdown();
}
private static void createConnection()
{
try
{
Class.forName("org.apache.derby.jdbc.ClientDriver").newInstance();
//Get a connection
conn = DriverManager.getConnection(dbURL);
}
catch (Exception except)
{
except.printStackTrace();
}
}
private static void insertRestaurants(int id, String restName, String cityName)
{
try
{
stmt = conn.createStatement();
stmt.execute("insert into " + tableName + " values (" +
id + ",'" + restName + "','" + cityName +"')");
stmt.close();
}
catch (SQLException sqlExcept)
{
sqlExcept.printStackTrace();
}
}
private static void selectRestaurants()
{
try
{
stmt = conn.createStatement();
ResultSet results = stmt.executeQuery("select * from " + tableName);
ResultSetMetaData rsmd = results.getMetaData();
int numberCols = rsmd.getColumnCount();
for (int i=1; i<=numberCols; i++)
{
//print Column Names
System.out.print(rsmd.getColumnLabel(i)+"\t\t");
}
System.out.println("\n-------------------------------------------------");
while(results.next())
{
int id = results.getInt(1);
String restName = results.getString(2);
String cityName = results.getString(3);
System.out.println(id + "\t\t" + restName + "\t\t" + cityName);
}
results.close();
stmt.close();
}
catch (SQLException sqlExcept)
{
sqlExcept.printStackTrace();
}
}
private static void shutdown()
{
try
{
if (stmt != null)
{
stmt.close();
}
if (conn != null)
{
DriverManager.getConnection(dbURL + ";shutdown=true");
conn.close();
}
}
catch (SQLException sqlExcept)
{
}
}
}
This code works fine but when I try to create a connection to the same database again with ij , I get an error in my command prompt like this:
In the image, the upper part is when I first make my database but after that when I use it in eclipse, it gives me this error. Even using a db in eclipse once will result in this error.
What is the issue? Why is derby engine not getting the access granted to it?
Any help is appreciated.
I suspect that you confused the database modes here. In your question's title you mention "embedded Derby", but you're code is using the ClientDriver and the create=true attribute, which does create the DB if it doesn't exist, but it doesn't start the server.
If you don't want to start the server, you can just use the EmbeddedDriver.
Another point where you might run into problems is with the shutdown=true attribute. You're using the entire DB URL (dbURL) including the filename, but if you want to shut down the server from your code, you should omit the filename, like this : jdbc:derby:;shutdown=true.
You can check out the Derby developer docs for information on using these attributes, and the Embedded Derby tutorial for using Derby in embedded mode, sou you won't have to worry about starting the server.
Found out the issue. I had to start the derby as a network server on the port by using the following command:
startNetworkServer.bat
I'm trying to execute method which should create a new object with fields from database, and everytime i run this code im getting SQLException: ResultSet closed.
public DatabasedClient getDatabaseClient(int clientDatabaseid){
if(DatabaseClientUtil.isInDatabase(clientDatabaseid)){
return DatabaseClientUtil.getDBClient(clientDatabaseid);
}else{
try{
System.out.println("Trying to find user in db");
ResultSet rs = fbot.getStorage().query("select * from database_name where clientDBId = " + clientDatabaseid);
System.out.println("deb " + rs.getString("nick"));
while (rs.next()) {
DatabasedClient databasedClient = new DatabasedClient(clientDatabaseid);
databasedClient.setUid(rs.getString("uid"));
databasedClient.setNick(rs.getString("nick"));
databasedClient.setLastConnect(rs.getLong("lastConnected"));
databasedClient.setLastDisconnect(rs.getLong("lastDisconnect"));
databasedClient.setTimeSpent(rs.getLong("timeSpent"));
databasedClient.setLongestConnection(rs.getLong("longestConnection"));
return databasedClient;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
return null;
}
}
Im using hikari, here are methods from AbstractStorage class
#Override
public void execute(String query) throws SQLException {
try (Connection connection = getConnection()){
connection.prepareStatement(query).executeUpdate();
}
}
#Override
public ResultSet query(String query) throws SQLException {
try (Connection connection = getConnection()) {
return connection.prepareStatement(query).executeQuery();
}
}
Screenshot from error
I hope someone will help me with this.
I think the exact error you are seeing is being caused by the following line of code:
System.out.println("deb " + rs.getString("nick"));
You are trying to access the result set before you advance the cursor to the first record. Also, your method getDatabaseClient is returning a single object which conceptually maps to a single expected record from the query. Hence, iterating once over the result set would seem to make sense. Taking all this into consideration, we can try the following:
try {
System.out.println("Trying to find user in db");
ResultSet rs = fbot.getStorage().query("select * from database_name where clientDBId = " + clientDatabaseid);
// do not access the result set here
if (rs.next()) {
DatabasedClient databasedClient = new DatabasedClient(clientDatabaseid);
databasedClient.setUid(rs.getString("uid"));
databasedClient.setNick(rs.getString("nick"));
databasedClient.setLastConnect(rs.getLong("lastConnected"));
databasedClient.setLastDisconnect(rs.getLong("lastDisconnect"));
databasedClient.setTimeSpent(rs.getLong("timeSpent"));
databasedClient.setLongestConnection(rs.getLong("longestConnection"));
return databasedClient;
}
} catch (SQLException e) {
e.printStackTrace();
}
first time posting so sorry if my question is slightly strange.
So I have a project in school that requires us to create java classes using netbeans that open up a window with three options, check stock, purchase item and update stock.
We had a class called stockdata that held the details of 5 different items for us to use in our three classes to check, purchase and update items. The latest stage of our coursework requires us to create a derby database and enter the items into a table.
I have done this with no issues but I am having a problem getting the items from the table back into my classes to use. We were given the following code but I can't get it to work, even using the commented hints.
package stock;
// Skeleton version of StockData.java that links to a database.
// NOTE: You should not have to make any changes to the other
// Java GUI classes for this to work, if you complete it correctly.
// Indeed these classes shouldn't even need to be recompiled
import java.sql.*; // DB handling package
import java.io.*;
import org.apache.derby.drda.NetworkServerControl;
public class StockData {
private static Connection connection;
private static Statement stmt;
static {
// standard code to open a connection and statement to an Access database
try {
NetworkServerControl server = new NetworkServerControl();
server.start(null);
// Load JDBC driver
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
//Establish a connection
String sourceURL = "jdbc:derby://localhost:1527/"
+ new File("UserDB").getAbsolutePath() + ";";
connection = DriverManager.getConnection(sourceURL, "use", "use");
stmt = connection.createStatement();
} // The following exceptions must be caught
catch (ClassNotFoundException cnfe) {
System.out.println(cnfe);
} catch (SQLException sqle) {
System.out.println(sqle);
} catch (Exception e) {
System.out.println(e);
}
}
// You could make methods getName, getPrice and getQuantity simpler by using an auxiliary
// private String method getField(String key, int fieldNo) to return the appropriate field as a String
public static String getName(String key) {
try {
// Need single quote marks ' around the key field in SQL. This is easy to get wrong!
// For instance if key was "11" the SELECT statement would be:
// SELECT * FROM Stock WHERE stockKey = '11'
ResultSet res = stmt.executeQuery("SELECT * FROM Stock WHERE stockKey = '" + key + "'");
if (res.next()) { // there is a result
// the name field is the second one in the ResultSet
// Note that with ResultSet we count the fields starting from 1
return res.getString(2);
} else {
return null;
}
} catch (SQLException e) {
System.out.println(e);
return null;
}
}
public static double getPrice(String key) {
// Similar to getName. If no result, return -1.0
return 0;
}
public static int getQuantity(String key) {
// Similar to getName. If no result, return -1
return 0;
}
// update stock levels
// extra is +ve if adding stock
// extra is -ve if selling stock
public static void update(String key, int extra) {
// SQL UPDATE statement required. For instance if extra is 5 and stockKey is "11" then updateStr is
// UPDATE Stock SET stockQuantity = stockQuantity + 5 WHERE stockKey = '11'
String updateStr = "UPDATE Stock SET stockQuantity = stockQuantity + " + extra + " WHERE stockKey = '" + key + "'";
System.out.println(updateStr);
try {
stmt.executeUpdate(updateStr);
} catch (SQLException e) {
System.out.println(e);
}
}
// close the database
public static void close() {
try {
connection.close();
} catch (SQLException e) {
// this shouldn't happen
System.out.println(e);
}
}
}
Sorry if this seems a stupid question but I am fairly new to Java and was making good progress until this roadblock.
Thanks in advance!
Alex
Searching for "java sql" on Google delivers this link: https://docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
From a connection you can create a statement (you can find this in the link and in your code) , then fetch a result set and loop over that with rs.next(). That should get your started.
Of course you have to make sure that the driver and database are there/running, just saying...
Here netbeans has nothing to do with database. This is a Java-based integrated development environment(IDE) that will help you to reduce syntactic error.
public void dataAccess(){
try {
String connectionUrl = "suitable connection url as per your database";
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
Class.forName("JDBC driver name as per your database");
con = DriverManager.getConnection(connectionUrl, userName, password);
String SQL = "SQL query as per your criteria";
stmt = con.createStatement();
rs = stmt.executeQuery(query);
while (rs.next()) {
// look into ResultSet api and use method as per your requirement
}
rs.close();
}
catch (Exception e) {
//log error message ;
}
}
im having a problem with my servlet whenever it was open from my JSP which is ShowPurchasingItems.jsp it will not go to the next JSP.
here is my ShowPurchasingItems.jsp
http://jsfiddle.net/0g3erumm/
and here is my Servlet that wont open my next JSP
package connection;
import java.io.*;
import java.sql.*;
import javax.servlet.http.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
#WebServlet("/CheckOutServlet")
public class CheckOutServlet extends HttpServlet
{
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
HttpSession session = request.getSession();
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
String User = (String) session.getAttribute("username");
String id = (String) session.getAttribute("stockIdToPurchase");
float price = (float) session.getAttribute("UnitPriceToPurchase");
int stock = (int) session.getAttribute("OnStockToPurchase");
int quantityOrdered = (int) session.getAttribute("purchaseQuantity");
float totalPrice = price * quantityOrdered;
int newStock = stock - quantityOrdered;
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String url = "jdbc:mysql://localhost:3306/inventory";
String user = "root";
String password = "password";
String query = "INSERT INTO purchases (username,stockId,price,quantityOrdered,totalPrice) VALUES ('"+User+"', '"+id+"', "+price+", "+quantityOrdered+", "+totalPrice+");";
try
{
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, user, password);
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
if(rs.next())
{
String encodedURL = response.encodeRedirectURL("ShowInventoryList.jsp");
response.sendRedirect(encodedURL);
}
}
catch(Exception e)
{
out.println("There is an error here");
}
finally
{
out.close();
try
{
rs.close();
stmt.close();
conn.close();
}
catch (Exception e)
{
out.println("There is no error here");
}
}
}
}
it would keep on catching error on this statment out.println("There is an error here"); and i am stuck in here i dont know what else is wrong with my program hope someone can help me.
You're committing a cardinal sin by swallowing the exception and thus losing all information that may help you get to the bottom of your problem!
You should change how your exceptions are handled, at the very least you should be dumping the stacktrace:
catch(Exception e) {
out.println("There is an error here");
e.printStackTrace();
}
Once you have the stacktrace you'll be in a much better situation when it comes to diagnosing the problem (or asking more specific questions)!
Edit - Based on the exception posted in the comment:
java.sql.SQLException: Can not issue data manipulation statements with executeQuery()
Is being thrown because you are performing an update using the query method. You should change your code to this:
int updateCount = stmt.executeUpdate(query);
if(updateCount > 0) {
String encodedURL = response.encodeRedirectURL("ShowInventoryList.jsp");
response.sendRedirect(encodedURL);
}
executeQuery executes the given SQL statement, which returns a single ResultSet object.
You're making INSERT, which doesn't return anything. I suppose that's why you're getting an exception.
I'd recommend to use PreparedStatement where you can bind variables and prevent SQL injection + some DB work faster with prepared statements, and executeUpdate instead of executeQuery
PreparedStatement stmt = null;
...
String query = "INSERT INTO purchases (username,stockId,price,quantityOrdered,totalPrice) VALUES (?, ?, ?, ?, ?)";
stmt = conn.prepareStatement(query);
stmt.setString(1, username);
...
int inserted = stmt.executeUpdate();
if (inserted > 0) {
// there was a successfull insert
...
There are a lot of examples on the Internet. For example: http://www.mkyong.com/jdbc/how-to-insert-date-value-in-preparedstatement/
I have a problem trying to execute more than one query into my Java Application code.
I have a procedure that is called in main and is in the class "Fant":
public void XXX(){
Connectivity con=new Connectivity(); // this class set up the data for the connection to db; if ( !con.connect() ) {
System.out.println("Error during connection.");
System.out.println( con.getError() );
System.exit(0);
}
ArrayList<User> blabla=new ArrayList<User>();
blabla=this.getAllUsers(con);
for (User u:blabla)
{
try {
Connectivity coni=new Connectivity();//start a new connection each time that i perform a query
Statement t;
t = coni.getDb().createStatement();
String query = "Select count(*) as rowcount from berebe.baraba";
ResultSet rs = t.executeQuery(query);
int numPrenotazioni=rs.getInt("rowcount");
rs.close(); //close resultset
t.close(); //close statement
coni.getDb().close(); //close connection
}
}
catch (SQLException e)
{
System.err.println("SQLState: " +
((SQLException)e).getSQLState());
System.err.println("Error Code: " +
((SQLException)e).getErrorCode());
}
}
}
The called function is defined as:
ArrayList<User> getAllUsers(Connectivity con) {
try{
ArrayList<User> userArrayList=new ArrayList<User>();
String query = "Select idUser,bubu,lala,sisi,gogo,gg from berebe.sasasa";
Statement t;
t = con.getDb().createStatement();
ResultSet rs = t.executeQuery(query);
while (rs.next())
{
User utente=new User(....); //user fields got from query
userArrayList.add(utente);
}
rs.close();
t.close();
con.disconnect(); //disconnect the connection
return userArrayList;
} catch (SQLException e) {
}
return null;
}
The main is:
public static void main(String[] argv) {
ArrayList<User> users=new ArrayList<User>();
System.out.println("-------- MySQL JDBC Connection Testing ------------");
Fant style = new Fant();
style.XXX();
}
The query performed into "getAllusers" is executed and into the arraylist "blabla" there are several users; the problem is that the second query that needs the count is never executed.
The MYSQlState given when running is= "S1000" and the SQLERROR is "0".
Probably i'm mistaking on connections issues but i'm not familiar with statements,connections,resultsets.
Thank you.
You might forget to call rs.next() before getting the result form it in XXX()methods as shown below:
ResultSet rs = t.executeQuery(query);
// call rs.next() first here
int numPrenotazioni=rs.getInt("rowcount");