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inserting new user object into JDBC through the servlet

Here is the code for my servlet which recieves username parameter from a registration form
String tusername=request.getParamater("un");
String dbURL="db.com";
String dbusername= "lc";
String dbpassword="lcpw";
Connection con=(Connection) DriverManager.getConnection(dbURL,dbusername,dbpassword);
Statement stmt= con.createStatement();
String query="SELECT * FROM users.username WHERE username=(tusername)";
ResultSet rs= stmt.executeQuery(query);
if(rs.next()==false){
//create new userobject with value of tusername
}
My question is how do I create a new user object with calue of tusername, would it be like so ?
if(rs.next()==false){
Statement stmt=con.createStatament();
String query="INSERT INTO user.username VALUE 'tusername'";
ResultSet rs= stmt.updateQuery(query);
}
I understand some of this might be archaic (such as not using a prepared statement) , I am just trying to better my understanding and I think I am having some small syntax issues, thanks :)

You should be using a NOT EXISTS query to do the insert, and also you should ideally be using a prepared statement:
String sql = "INSERT INTO user.username (username) ";
sql += "SELECT ? FROM dual WHERE NOT EXISTS (SELECT 1 FROM user.username WHERE username = ?)";
PreparedStatement ps = con.prepareStatement(sql);
ps.setString(1, tusername);
ps.setString(2, tusername);
int result = ps.executeUpdate();
if (result > 0) {
System.out.println("Inserted new user " + tusername + " into username table";
}
else {
System.out.println("User " + tusername + " already exists; no new record was inserted");
}
I don't know what your actual database is. The above should work out of the box for MySQL and Oracle. It might need to be modified slightly for other databases.
An alternative to the above query would be to just use your current insert, but make the username column a (unique) primary key. In that case, any attempt to insert a duplicate would fail at the database level, probably resulting in an exception in your Java code. This would also be a more database agnostic approach.

SQL query for updating column with values from a local variable

How can I update my SQL Table column with the value that is stored in a local variable.
In my program I have taken value from the HTML page using the following statement:
String idd=request.getParameter("id");
String report=request.getParameter("rprt");
So now I have to update the value of report in my database table named "ptest" and I am using the following query:
Class.forName("com.mysql.jdbc.Driver");
java.sql.Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/tcs","root","root");
Statement st= con.createStatement();
ResultSet rs;
int i=st.executeUpdate("update ptest set result = #reprt where patient_id=
#idd");
out.println("Successfully Entered");
But the value is not being stored in the database instead NULL is being stored.
I have already seen this question and got no help.
Question
Please ignore my mistakes if any in this question as I am new to MYSQL.

You can use prepared statements in java.
setString or setInt can set different data types into your prepared statements.
The parameter 1, 2 are basically the positions of the question mark. setString(1,report) means that it would set the string report in the 1st question mark in your query.
Hope this code helps you in achieving what you want.
String query = "update ptest set result = ? where patient_id = ?";
PreparedStatement preparedStatement = con.prepareStatement(query);
preparedStatement.setString(1, report);
preparedStatement.setString(2, idd);
preparedStatement.executeUpdate();

In JDBC, you use ? as placeholders for where you want to inject values into a statement.
So you should do something like this ...
Class.forName("com.mysql.jdbc.Driver");
java.sql.Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/tcs","root","root");
PreparedStatement st= con.prepareCall("update ptest set result = ? where patient_id=
?");
///now set the params in order
st.setString(1, report);
st.setString(2, idd);
//then execute
st.executeUpdate();
Doing a string concat with the values is dangerous due to sql injection possibilities, so I typically make statement text static and final, and also if your value has a ' in it that could blow up your sql syntax etc. Also, notice the use of executeUpdate rather than query.
Hope this helps

SQLite Query With Parameters Not Working in Java

I have a program that selects from a database given a table and column string.
public void selectAllFrom(String table, String column){
String sql = "SELECT ? FROM ?";
try (Connection conn = this.connect();
PreparedStatement pstmt = conn.prepareStatement(sql)){
pstmt.setString(1, column);
pstmt.setString(2, table);
ResultSet rs = pstmt.executeQuery();
while (rs.next()){
System.out.println(rs.getString(column));
}
} catch (SQLException e){
System.out.println(" select didn't work");
System.out.println(e.getMessage());
}
}
For some reason it is not working and it is going right to catch
Here is the connect() function as well:
private Connection connect(){
Connection conn = null;
// SQLite connection string
String url = "jdbc:sqlite:C:/sqlite/db/chinook.db";
try{
// creates connection to the database
conn = DriverManager.getConnection(url);
System.out.println("Connection to SQLite has been established");
} catch (SQLException e){
System.out.println(e.getMessage());
System.out.println("Connection didn't work");
}
return conn;
}
I know the problem is not with the database because I'm able to run other select queries without parameters. It is the parameters that are giving me the problem. Can anyone tell what the problem is?

A table or column name can't be used as a parameter to PreparedStatement. It must be hard coded.
String sql = "SELECT " + column + " FROM " + table;
You should reconsider the design so as to make these two constant and parameterize the column values.

? is a place holder to indicate a bind variable. When a SQL statement is executed, database first checks syntax, and validates the objects being referenced, columns and access permission for specified objects (i.e metadata about objects) and confirms that all are in place and valid. This stage is called parsing.
Post parsing, it substitutes bind variables to query and then proceeds for actual fetch of results.
Bind variables can be substituted in any place in query to replace an actual hard coded data/strings, but not the query constructs them selves. It means
You can not use bind variables for keywords of sql query (ex: SELECT, UPDATE etc.)
You can not use bind variables for objects or their attributes (i.e table names, column names, functions, procedures etc.)
You can use them only in place of a otherwise hard coded data.
ex: SELECT FIRST_NAME, LAST_NAME, 'N' IS_DELETED FROM USER_DATA WHERE COUNTRY ='CANADA' AND VERIFIED_USER='YES'
In above sample query, 'N','CANADA' and 'YES' are the only strings which can be replaced by a bind variable, not any other word.
Using bind variable is best practice of coding. It improves query performance (when used with large no. of queries in tuned database products like Oracle or MSSQL) and also protects your code against sql injection attacks.
Constructing query by concatenating strings (especially data part of query) is never recommended way. You can still construct a query by concatenation for other parts like table name or column name as long as those strings are not directly taken from input.
Below example is acceptable:
query = "Select transaction_id, transaction_date from ";
if (isHistorical(reportType)
{ query = query + "HISTORY_TRANSACTIONS" ;}
else
{query = query + "PRESENT_TRANSACTIONS" ; }
recommended practice is to use
String query_present = "SELECT transaction_id, transaction_date from PRESENT_TRANSACTIONS";
String query_historical = "SELECT transaction_id, transaction_date from HISTORY_TRANSACTIONS";
if (isHisotrical(reportType))
{
ps.executeQuery(query_historical);
}else{
ps.executeQuery(query_present);
}

How to insert two strings into my Access database from Java using UCanAccess?

I am trying to add two strings on two separate columns columns of my database using Java but I'm not sure what I am doing wrong. The code I am using
try{
Connection conn = DriverManager.getConnection(
"jdbc:ucanaccess://C:/Users/nevik/Desktop/databaseJava/Employee.accdb");
Statement st = conn.createStatement();
String sql = "Select * from Table2";
ResultSet rs = st.executeQuery(sql);
rs.updateString("user", user);
rs.updateString("pass", pass);
rs.updateRow();
}
catch(SQLException ex){
System.err.println("Error: "+ ex);
}
The first column on my database is user and the next one is pass. I am using UCanAccess in order to access my database.

This is how you normally update a row in java:
String query = "update Table2 set user = ?, pass= ?";
PreparedStatement preparedStmt = conn.prepareStatement(query);
preparedStmt.setInt (1, user);
preparedStmt.setString(2, pass);
// execute the java preparedstatement
preparedStmt.executeUpdate();

First of, you've not updated the position of the current cursor in the ResultSet, which means that it's pointing to nothing...
You could use...
if (rs.next()) {
rs.updateString("user", user);
rs.updateString("pass", pass);
rs.updateRow();
}
But this assumes two things...
You have a database that supports updating values in the ResultSet and
You want to update the existing values.
To insert a value into the database, you should be using the INSERT command, for example...
try(Connection conn = DriverManager.getConnection(
"jdbc:ucanaccess://C:/Users/nevik/Desktop/databaseJava/Employee.accdb")) {
try (PreparedStatement stmt = conn.prepareStatement("INSERT into Table2 (user, pass) VALUES (?, ?)") {
stmt.setString(1, user);
stmt.setString(2, pass);
int rowsUpdated = stmt.executeUpdate();
}
}
catch(SQLException ex){
System.err.println("Error: "+ ex);
}
You might like to take some time to go over a basic SQL tutorial and the JDBC(TM) Database Access trail
As a side note...
You should not be storing passwords in Strings, you should keep them in char arrays and
You should not be storing passwords in the database without encrypting them in some way

#guevarak12
About the original question (how to use updatable ResultSet):
your code is wrong, you have to move the cursor in the right position.
In particular, if you are inserting a new row you have to call rs.moveToInsertRow(); before rs.updateString("user", user).
If you are updating an existent row, you have to move the cursor calling rs.next() and so reach the row to update.
Also you have to create the Statement in a different way:
Statement st =conn.createStatement( ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE);
See junit examples in the UCanAccess source distribution, class net.ucanaccess.test.CrudTest.
All other comments seem to be correct.

Is there a way to retrieve the autoincrement ID from a prepared statement

Is there a way to retrieve the auto generated key from a DB query when using a java query with prepared statements.
For example, I know AutoGeneratedKeys can work as follows.
stmt = conn.createStatement();
stmt.executeUpdate(sql, Statement.RETURN_GENERATED_KEYS);
if(returnLastInsertId) {
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}
However. What if I want to do an insert with a prepared Statement.
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql);
//this is an error
stmt.executeUpdate(Statement.RETURN_GENERATED_KEYS);
if(returnLastInsertId) {
//this is an error since the above is an error
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}
Is there a way to do this that I don't know about. It seems from the javadoc that PreparedStatements can't return the Auto Generated ID.

Yes. See here. Section 7.1.9. Change your code to:
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
stmt.executeUpdate();
if(returnLastInsertId) {
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}

There's a couple of ways, and it seems different jdbc drivers handles things a bit different, or not at all in some cases(some will only give you autogenerated primary keys, not other columns) but the basic forms are
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
Or use this form:
String autogenColumns[] = {"column1","column2"};
stmt = conn.prepareStatement(sql, autogenColumns)

Yes, There is a way. I just found this hiding in the java doc.
They way is to pass the AutoGeneratedKeys id as follows
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);

I'm one of those that surfed through a few threads looking for solution of this issue ... and finally get it to work. FOR THOSE USING jdbc:oracle:thin: with ojdbc6.jar PLEASE TAKE NOTE:
You can use either methods:
(Method 1)
Try{
String yourSQL="insert into Table1(Id,Col2,Col3) values(SEQ.nextval,?,?)";
myPrepStatement = <Connection>.prepareStatement(yourSQL, Statement.RETURN_GENERATED_KEYS);
myPrepStatement.setInt(1, 123);
myPrepStatement.setInt(2, 123);
myPrepStatement.executeUpdate();
ResultSet rs = getGeneratedKeys;
if(rs.next()) {
java.sql.RowId rid=rs.getRowId(1);
//what you get is only a RowId ref, try make use of it anyway U could think of
System.out.println(rid);
}
} catch (SQLException e) {
//
}
(Method 2)
Try{
String yourSQL="insert into Table1(Id,Col2,Col3) values(SEQ.nextval,?,?)";
//IMPORTANT: here's where other threads don tell U, you need to list ALL cols
//mentioned in your query in the array
myPrepStatement = <Connection>.prepareStatement(yourSQL, new String[]{"Id","Col2","Col3"});
myPrepStatement.setInt(1, 123);
myPrepStatement.setInt(2, 123);
myPrepStatement.executeUpdate();
ResultSet rs = getGeneratedKeys;
if(rs.next()) {
//In this exp, the autoKey val is in 1st col
int id=rs.getLong(1);
//now this's a real value of col Id
System.out.println(id);
}
} catch (SQLException e) {
//
}
Basically, try not used Method1 if you just want the value of SEQ.Nextval, b'cse it just return the RowID ref that you may cracked your head finding way to make use of it, which also don fit all data type you tried casting it to! This may works fine (return actual val) in MySQL, DB2 but not in Oracle.
AND, turn off your SQL Developer, Toad or any client which use the same login session to do INSERT when you're debugging. It MAY not affect you every time (debugging call) ... until you find your apps freeze without exception for some time. Yes ... halt without exception!

Connection connection=null;
int generatedkey=0;
PreparedStatement pstmt=connection.prepareStatement("Your insert query");
ResultSet rs=pstmt.getGeneratedKeys();
if (rs.next()) {
generatedkey=rs.getInt(1);
System.out.println("Auto Generated Primary Key " + generatedkey);
}