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Data i've inserted into table does not replace old data, is there a way to replace data if it's already there?

Problem is the following: I am saving hashed password for a school project, however i am stuck on the syntax for the SQL statement to replace the data if it is already present. The table will only need to store a single username/password combination.
public class DatabaseManager {
String dbPath = "jdbc:sqlite:test.db";
public DatabaseManager () {
try {
Class.forName("org.sqlite.JDBC");
Connection conn = DriverManager.getConnection(dbPath);
if (conn != null) {
System.out.println("Connected to the database");
DatabaseMetaData dm = (DatabaseMetaData) conn.getMetaData();
// Setting up database
databaseSetup(conn);
boolean tempInsertion = databaseInsert("pancake", "house", conn);
// Inserting data
if (tempInsertion) {
System.out.println("Data insertion failed");
}
// Retrieving data
List<String> retrievedData = databaseSelect(conn);
if (retrievedData == null) {
System.out.println("Data extraction failed");
}
else {
System.out.println(retrievedData.size());
}
conn.close();
}
}
catch (ClassNotFoundException ex) {
ex.printStackTrace();
} catch (SQLException ex) {
ex.printStackTrace();
}
}
private boolean databaseInsert(String username, String password, Connection conn) {
String sqlInsert = "INSERT OR REPLACE INTO login(username, password) VALUES(?,?)";
PreparedStatement prepStatement;
try {
prepStatement = conn.prepareStatement(sqlInsert);
prepStatement.setString(1, encrypt(username));
prepStatement.setString(2, encrypt(password));
prepStatement.executeUpdate();
} catch (SQLException e) {
return false;
}
return true;
}
private List<String> databaseSelect(Connection conn) {
List<String> tempList = new ArrayList<String>();
String sqlSelect = "SELECT * FROM login";
Statement stmt;
try {
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sqlSelect);
tempList.add(rs.getString("username"));
tempList.add(rs.getString("password"));
int columnsNumber = rs.getMetaData().getColumnCount();
while (rs.next()) {
for (int i = 1; i <= columnsNumber; i++) {
if (i > 1) System.out.print(", ");
String columnValue = rs.getString(i);
System.out.print(columnValue + " " + rs.getMetaData().getColumnName(i));
}
System.out.println("");
}
} catch (SQLException e) {
return null;
}
return tempList;
}
private void databaseSetup( Connection conn) {
String sqlExpression = "CREATE TABLE login (username varchar(255), password varchar(255))";
try {
Statement statement = conn.createStatement();
statement.execute(sqlExpression);
} catch (SQLException e) {}
}
private String encrypt(String string) {
try {
MessageDigest exampleCrypt = MessageDigest.getInstance("SHA1");
exampleCrypt.reset();
exampleCrypt.update(string.getBytes("UTF-8"));
return convertByte(exampleCrypt.digest());
}
catch(NoSuchAlgorithmException e) {
System.out.println("Error, cannot encrypt string");
e.printStackTrace();
}
catch(UnsupportedEncodingException e) {
System.out.println("Error, cannot encrypt string");
e.printStackTrace();
}
return null;
}
private static String convertByte(final byte[] hash) {
Formatter formatter1 = new Formatter();
for (byte i : hash) {
formatter1.format("%02x", i);
}
String encryptedData = formatter1.toString();
formatter1.close();
return encryptedData;
}
}
The problem as stated, is that i'd like to only store a single password/username combination at a time, as a hash. However, when this happens it duplicates the hash combination, instead of replacing it.

jFrame fields not saving to db

Am trying to save some field from my jFrame form but when i click the save button, i get the null pointer exception. Previously i was getting the errors that text field couldn't be null so i unchecked not null but it didn't work , i decided not to include Voucher_no in MySQL insert statement as it is an auto increment and its text field is not editable
Is there any problem with my code?
Am Using Mysql Workbench.
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");
con.setAutoCommit(false);
try {
// String kb = jTextField3.getText(); //voucher_no
String kc = (String) jComboBox3.getSelectedItem(); //factory
String kg = jTextField10.getText(); //fuel
Double ks = Double.valueOf(kg);
String ke = jTextField11.getText(); //electricity
Double kt = Double.valueOf(ke);
String kf = jTextField12.getText(); //manpower
Double ku = Double.valueOf(kf);
String kj = (String) jComboBox4.getSelectedItem(); //can_name
String kk = (String) jComboBox5.getSelectedItem(); //label name
String kq = jTextField23.getText();//no_of_cans
Double kv = Double.valueOf(kq);
String kr = jTextField24.getText();//no_of_labels
Double kw = Double.valueOf(kr);
String query1= "insert into production (date,factory,fuel,electricity,manpower,can_name,label_name,no_of_cans,no_of_labels)"
+ "values (?,?,?,?,?,?,?,?,?)";
try (PreparedStatement pst = con.prepareStatement(query1)){
// pst.setString(10, kb);
pst.setString(1, ((JTextField) jDate1.getDateEditor().getUiComponent()).getText());
pst.setString(2, kc);
pst.setDouble(3, ks);
pst.setDouble(4, kt);
pst.setDouble(5, ku);
pst.setString(6, kj);
pst.setString(7, kk);
pst.setDouble(8, kv);
pst.setDouble(9, kw);
pst.execute();
}
try {
int rows = jTable2.getRowCount();
for (int row = 0; row < rows; row++) {
String kd = (String) jTable2.getValueAt(row, 0);
Double kn = (Double) jTable2.getValueAt(row, 1);
try {
// Class.forName("com.mysql.jdbc.Driver").newInstance();
// Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");
String query = "insert into production(product_name,product_quantity)"
+ "values (?,?)";
PreparedStatement update = con.prepareStatement(query);
update.setString(1, kd);
update.setDouble(2, kn);
update.addBatch();
update.executeBatch();
con.commit();
} catch (SQLException e) {
e.printStackTrace();
// JOptionPane.showMessageDialog(this, "Error in production Table");
}
}
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Invalid Entry in fields");
}
} catch (Exception e) {
e.printStackTrace();
// JOptionPane.showMessageDialog(null, "Invalid in fields");
}
} catch (Exception e) {
e.printStackTrace();
}

The code is doing
update.addBatch();
update.executeBatch();
con.commit();
executeBatch and commit must be done outside the loop.
The misunderstanding arises from "addBatch" that should have been named "addToBatch."

Try doing it this way. First create a connection class as follows;
import java.sql.Connection;
import java.sql.DriverManager;
public class db_connection
{
public Connection connection()
throws Exception
{
try
{
Connection conn = null;
String username = "root"; String password = "";
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/database";
try {
Class.forName(driver);
} catch (Exception e) {
e.printStackTrace();
return null;
}
conn = DriverManager.getConnection(url, username, password);
conn.setAutoCommit(false);
return conn;
} catch (Exception e) {
e.printStackTrace();
System.exit(0);
}return null;
}
}
Then on your save button do something like this,
private void ButtonRegGroup_SubmitActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
if ((this.jTextFieldGrp_ReqAmnt.getText().equals(""))
|| (this.jTextFieldGrp_name.getText().equals(""))
|| (this.jTextFieldGrp_Id.getText().equals(""))
|| (this.jTextFieldGrp_prj_name.getText().equals(""))) {
JOptionPane.showMessageDialog(this, "Some fields are empty", this.title, this.error);
} else {
try {
this.con = ((Connection) new db_connection().connection());
this.pst = ((PreparedStatement) this.con.prepareStatement("insert into registered_projects(project_type,name,project_name,project_id,constituency,ward,requested_amount)values(?,?,?,?,?,?,?)"));
GroupRegDetails();
this.pst.setString(1, this.proj_type);
this.pst.setString(2, this.group_name);
this.pst.setString(3, this.proj_name);
this.pst.setInt(4, this.proj_id);
this.pst.setString(5, this.constituency);
this.pst.setString(6, this.ward);
this.pst.setInt(7, this.requested_amount);
int row = this.pst.executeUpdate();
con.commit();
if (row == 0) {
this.con.rollback();
JOptionPane.showInternalMessageDialog(this, "Didn't Register project", this.title, this.error);
}
JOptionPane.showMessageDialog(this, "Project Successfully Registered", this.title, this.infor);
} catch (Exception e) {
e.printStackTrace();
}
}
}
public void GroupRegDetails() {
this.group_name = this.jTextFieldGrp_name.getText();
this.proj_id = Integer.parseInt(this.jTextFieldGrp_Id.getText());
this.proj_name = this.jTextFieldGrp_prj_name.getText();
this.constituency = this.jComboBoxGrp_Comb_const.getSelectedItem().toString();
this.ward = this.jComboBoxGrp_comb_Ward.getSelectedItem().toString();
this.requested_amount = Integer.parseInt(this.jTextFieldGrp_ReqAmnt.getText());
this.proj_type = "Group";
}
And finally good practice is to put fields on a Jpanel and the Jpanel on a Jframe. Hope this helps.

indexof string matching from data base and runtime text

I want to make website blocker in my web browser, so I made a database which contain the names of website. Now I want to check the string from database with indexOf method, but it is giving me an error while I am trying to check. Please tell me where my mistake is. Rest of the code is correct and working only database part is not working.
public void loadURL(final String url) {
try {
Connection myconnection;
myconnection = DriverManager.getConnection("jdbc:mysql://localhost/bookmarks", "roo t", "");
try {
String q = "select * from block where url=?";
PreparedStatement mysat = myconnection.prepareStatement(q);
ResultSet myresult = mysat.executeQuery();
int index1;
while (myresult.next()) {
String s2 = myresult.setString("url");
String s1 = txtURL.getText();
index1 = s1.indexOf(s2);
}
if (index1 == -1) {
JOptionPane.showMessageDialog(rootPane, "You Cannot access this website", "Error", JOptionPane.ERROR_MESSAGE);
} else {
Platform.runLater(new Runnable() {
#Override
public void run() {
String tmp = toURL(url);
if (tmp == null) {
tmp = toURL("http://" + url);
}
engine.load(tmp);
}
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
myconnection.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}

if you use PreparedStatement you have to set a
value for each ? marker:
String q="select * from block where url=?";
PreparedStatement mysat=myconnection.prepareStatement(q);
mysat.setString(1,"www.google.com");
without you have an invalid sql syntax.

Display details on specific user using rest web service, queryparam

I am making a log in form on java. Restful web service. I have done logging in and in registration. I have here inputting plate number. I want to retrieve data based on the inputted plate number. I have here the scanning only of the plate number if it is in the database, but I dont know how to display the details of it. Here's my code. I'm so confused. I don't know how to do it.
Constants.java
package com.taxisafe.connection;
public class Constants {
public static String dbClass = "com.mysql.jdbc.Driver";
private static String dbName= "taxisafe";
public static String dbUrl = "jdbc:mysql://localhost:3306/"+dbName;
public static String dbUsername = "root";
public static String dbPassword = "";
}
DatabaseConnection.java
package com.taxisafe.connection;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import com.taxisafe.objects.Objects;
public class DatabaseConnection {
#SuppressWarnings("finally")
public static Connection createConnection() throws Exception {
Connection koneksyon = null;
try {
Class.forName(Constants.dbClass);
koneksyon = DriverManager.getConnection(Constants.dbUrl, Constants.dbUsername, Constants.dbPassword);
} catch (Exception e) {
throw e;
} finally {
return koneksyon;
}
}
//CHECK FOR LOGIN
public static boolean checkUser(String username, String password) throws Exception { //checkLogin to checkUser
boolean UserRecorded = false;
Connection konek = null;
try {
try {
konek = DatabaseConnection.createConnection();
} catch (Exception e) {
e.printStackTrace();
}
Statement statement = konek.createStatement();
String code = "SELECT * FROM user WHERE username = '" + username + "' AND password=" + "'" + password + "'";
ResultSet rs = statement.executeQuery(code);
while (rs.next()) {
UserRecorded = true;
}
} catch (SQLException sqle) {
throw sqle;
} catch (Exception e) {
// TODO Auto-generated catch block
if (konek != null) {
konek.close();
}
throw e;
} finally {
if (konek != null) {
konek.close();
}
}
return UserRecorded;
}
// REGISTER USER
public static boolean registertheUser(String name, String username, String email, String password) throws SQLException, Exception { //inserUser - registertheUser
boolean insertUser = false; //insertStatus - insertUser
Connection konek = null;
try{
try{
konek = DatabaseConnection.createConnection();
}
catch (Exception e){
e.printStackTrace();
}
Statement statement = konek.createStatement();
String code = "INSERT into user(name, username, emailaddress, password) values('"+name+ "',"+"'" + username + "','"+ email + "','" + password + "')";
int dbrecord = statement.executeUpdate(code);
if (dbrecord > 0){
insertUser = true;
}
} catch (SQLException sqle){
throw sqle;
} catch (Exception e){
if (konek !=null){
konek.close();
}
throw e;
} finally{
if (konek !=null){
konek.close();
}
} return insertUser;
}
//CHECK PLATE NUMBER
public static boolean checkPlate(String platenumber) throws Exception { //checkLogin to checkUser
boolean PlateRecorded = false;
Connection konek = null;
try {
try {
konek = DatabaseConnection.createConnection();
} catch (Exception e) {
e.printStackTrace();
}
Statement statement = konek.createStatement();
String code = "SELECT * FROM taxi WHERE taxi_plate_no = '" + platenumber+ "'";
ResultSet rs = statement.executeQuery(code);
while (rs.next()) {
PlateRecorded = true;
}
} catch (SQLException sqle) {
throw sqle;
} catch (Exception e) {
// TODO Auto-generated catch block
if (konek != null) {
konek.close();
}
throw e;
} finally {
if (konek != null) {
konek.close();
}
}
return PlateRecorded;
}
}
JsonConstruction.java
package com.taxisafe.json;
import org.codehaus.jettison.json.JSONException;
import org.codehaus.jettison.json.JSONObject;
public class JsonConstruction {
public static boolean isNotNull(String text){
return text !=null && text.trim().length() >=0 ? true : false;
}
public static String JSONResponse(String tag, boolean status){
JSONObject object = new JSONObject();
try{
object.put("tag", tag);
object.put("status", new Boolean(status));
} catch (JSONException e){
} return object.toString();
}
public static String JSONResponse(String tag, boolean status, String errorMessage){
JSONObject object = new JSONObject();
try{
object.put("tag", tag);
object.put("status", new Boolean(status));
object.put("errorMessage", errorMessage);
} catch (JSONException e){
} return object.toString();
}
}
PlateNumberCheck.java
package com.taxisafe.server;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import com.sun.corba.se.impl.util.Utility;
import com.taxisafe.connection.DatabaseConnection;
import com.taxisafe.json.JsonConstruction;
#Path("platecheck") //for the url
public class PlateNumberCheck {
#GET
//To get the full url : http://Ipaddress:portnumber/#path/#getPath
#Path("/magcheck")
#Produces(MediaType.APPLICATION_JSON)
//Produces is for the response of JSON.
public String magcheck(#QueryParam("platenumber") String platenumber){
String sagot = "";
if(checkInput(platenumber)){
sagot = JsonConstruction.JSONResponse("checked", true);
} else{
sagot = JsonConstruction.JSONResponse("checked", false, "Not in the database");
}
return sagot;
}
private boolean checkInput (String platenumber){
System.out.println("Check Input");
boolean output = false;
if(JsonConstruction.isNotNull(platenumber)){
try{
output = DatabaseConnection.checkPlate(platenumber);
} catch (Exception e){
output = false;
}
} else{
output = false;
}
return output;
}
}
Please help me on how to display the details of the plate number.

NullPointerException on statement.executeUpdate() [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
I created a website with JSP and Java, it simply displays a form (it's a user registration form) where the user can fill it, then I want it to be stored in a database.
I installed Eclipse, Tomcat (to host on localhost 8080) and Wampserver (to have phpmyadmin and my SQL database).
I've tried to create an ORM (Object-relational mapping), so when the client submits the form, it sends the datas to my ORM, my ORM then stores the datas in my database.
The issue is, when the user submit submits the form, my table is created (I can see it on phpmyAdmin), so it's very good. But it crashes on my website and creates an error
HTTP500, java.lang.NullPointerException.
It says the problem is on
com.jweb.bdd.Orm.Perform(Orm.java:139)
Here is my code in my CreateClient.java file, this java file handles the servlet of my registration form:
public class CreationClient extends HttpServlet {
public void doGet( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException {
[...]
String lastName= request.getParameter( CHAMP_LASTNAME);
String Name= request.getParameter( CHAMP_NAME);
String mailAdress = request.getParameter( CHAMP_MAILADRESS);
String phoneNumber= request.getParameter( CHAMP_PHONENUMBER);
String login= request.getParameter( CHAMP_LOGIN);
[...]
Orm orm = new Orm();
String[] field = {"login", "firstName", "lastName", "mailAdress", "adress", "phoneNumber", "password"};
String[] values = {login, firstName, lastName, mailAdress, adress, phoneNumber, password};
orm.Insert("client", field);
orm.Values(values);
orm.Perform();
orm.CloseConnection();
[...]
}
}
Here is my Perfom() function in my ORM class:
public void Perform(){
ResultSet rst = null;
if (select != null){
if (from != null && where != null){
try {
rst = statement.executeQuery(select + from + where);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
int i = 0;
while (rst.next()){
res[i] = rst.getString(0) + ":" + rst.getString(1)+ ":" + rst.getString(3) + ":" + rst.getString(4) +":" + rst.getString(5) + ":" + rst.getString(6)+ ":" + rst.getString(7) + ";";
i++;
}
} catch (SQLException e){
e.printStackTrace();
}
}
}
else if (insert != null){
if (values != null){
try {
// statement = connexion.creatStatemnt();
int res = statement.executeUpdate(insert + values);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
try {
rst.close();
} catch (SQLException ignore){
}
if ( statement != null ) {
try {
statement.close();
} catch ( SQLException ignore ) {
}
}
}
And the error on the line 139 is the int res = statement.executeUpdate(insert + values); :
else if (insert != null){
if (values != null){
try {
int res = statement.executeUpdate(insert + values);
} catch (SQLException e) {
e.printStackTrace();
}
}
Do you have any idea how to fix this issue of NullPointer?
Thanks.

You need to initialize your statement object, In your code you used statement.executeQuery() but not statement = connection.createStatement() initialize statement object.