When I execute the following code, I get an exception. I think it is because I'm preparing in new statement with he same connection object. How should I rewrite this so that I can create a prepared statement AND get to use rs2? Do I have to create a new connection object even if the connection is to the same DB?
try
{
//Get some stuff
String name = "";
String sql = "SELECT `name` FROM `user` WHERE `id` = " + userId + " LIMIT 1;";
ResultSet rs = statement.executeQuery(sql);
if(rs.next())
{
name = rs.getString("name");
}
String sql2 = "SELECT `id` FROM `profiles` WHERE `id` =" + profId + ";";
ResultSet rs2 = statement.executeQuery(sql2);
String updateSql = "INSERT INTO `blah`............";
PreparedStatement pst = (PreparedStatement)connection.prepareStatement(updateSql);
while(rs2.next())
{
int id = rs2.getInt("id");
int stuff = getStuff(id);
pst.setInt(1, stuff);
pst.addBatch();
}
pst.executeBatch();
}
catch (Exception e)
{
e.printStackTrace();
}
private int getStuff(int id)
{
try
{
String sql = "SELECT ......;";
ResultSet rs = statement.executeQuery(sql);
if(rs.next())
{
return rs.getInt("something");
}
return -1;
}//code continues
The problem is with the way you fetch data in getStuff(). Each time you visit getStuff() you obtain a fresh ResultSet but you don't close it.
This violates the expectation of the Statement class (see here - http://docs.oracle.com/javase/7/docs/api/java/sql/Statement.html):
By default, only one ResultSet object per Statement object can be open at the same time. Therefore, if the reading of one ResultSet object is interleaved with the reading of another, each must have been generated by different Statement objects. All execution methods in the Statement interface implicitly close a statment's current ResultSet object if an open one exists.
What makes things even worse is the rs from the calling code. It is also derived off-of the statement field but it is not closed.
Bottom line: you have several ResultSet pertaining to the same Statement object concurrently opened.
A ResultSet object is automatically
closed when the Statement object that
generated it is closed, re-executed,
or used to retrieve the next result
from a sequence of multiple results.
I guess after while(rs2.next()) you are trying to access something from rs1. But it's already closed since you reexecuted statement to get rs2 from it. Since you didn't close it, I beleive it's used again below.
Related
This question already has answers here:
Java MYSQL Prepared Statement Error: Check syntax to use near '?' at line 1
(2 answers)
Closed 1 year ago.
I faced this problem today with my select SQL. This method is supposed to show data from database in tex tfields. I changed it from statement to preparedStatement, but I faced a problem.
public Entreprise loadDataModify(String id) {
Entreprise e = new Entreprise();
PreparedStatement stmt;
try {
String sql = "SELECT * FROM user WHERE mail=?";
stmt = cnx.prepareStatement(sql);
stmt.setString(1, id);
ResultSet rst = stmt.executeQuery(sql);
while (rst.next()) {
stmt.setString(2, e.getNom());
stmt.setString(3, e.getEmail());
stmt.setString(4, e.getTel());
stmt.setString(5, e.getOffre());
}
} catch (SQLException ex) {
System.out.println(ex.getMessage());
}
return e;
}
It shows i have problem with syntax and the output is " nu
You're calling the wrong method. Unlike Statement, when you're using a PreperedStatement you should first set the values for the parameters, and after you can call on that instance executeQuery() method.
Also, it's a best practice to use try-with-resources, because a Statement or PreparedStament object is a Resource (a resource is a class that implements AutoCloseable interface) and you have to close it. Using try-with-resources, it's done automatically.
The ResultSet instance is also a resource, but it's closed when the statement object is closed, so you don't have to close it explicitly.
So, the best way to solve your problem will be:
String selectAllByMail = "SELECT * FROM user WHERE mail=?";
try (PreparedStatement prpStatement = connection.prepareStatement(selectAllByMail)) {
// use prpStatement
prpStatement.setString(1, id);
ResultSet resultSet = prpStatement.executeQuery();
while (resultSet.next()) {
// process resultSet
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}
You are not filling your Enterprise object. And you are not using executeQuery() function correctly. As seen below, the parameter inside the brackets has been removed. PreparedStatements first of all need the values of the parameters (your ? in the query) and then the formed query has to be executed. If you give a String parameter to executeQuery() then the query in the brackets will be executed.
And the part where Enterprise is being filled could be seen below.
This would be the correct way:
public Entreprise loadDataModify(String id) {
Entreprise e = new Entreprise();
PreparedStatement stmt;
try {
String sql = "SELECT * FROM user WHERE mail=?";
stmt = cnx.prepareStatement(sql);
stmt.setString(1, id);
ResultSet rst = stmt.executeQuery();
while (rst.next())
{
// rst keeps the data, so you have to traverse it and get the data from it in this way.
e.setNom( rst.getString("HERE EITHER THE COLUMN NAME OR INDEX"));
e.setEmail( rst.getString("HERE EITHER THE COLUMN NAME OR INDEX"));
e.setTel( rst.getString("HERE EITHER THE COLUMN NAME OR INDEX"));
e.setOffre( rst.getString("HERE EITHER THE COLUMN NAME OR INDEX"));
}
} catch (SQLException ex) {
System.out.println(ex.getMessage());
}
return e;
}
Your call to executeQuery() should not be passing the query string. Use this version:
String sql = "SELECT * FROM user WHERE mail=?";
stmt = cnx.prepareStatement(sql);
stmt.setString(1, id);
ResultSet rst = stmt.executeQuery();
while (rst.next()) {
// process result set
}
Your current code is actually calling some overloaded Statement#executeQuery() method, which is not the version of the method which you want to be calling.
I have a strange problem. I have a database and I want to change the values of a column. The values are safed in an Arraylist (timelist).
In order to write the values in the right row, I have a second Arrylist (namelist). So I want to read the first row in my Database, than I check the namelist and find the name. Than i take the matching value out of the timelist and write it into the database into the column "follows_date" in the row, matching to the name.
And than I read the next row of the Database, until there are no more entries.
So the strange thing is, if I change nothing in the database, the while(rs.next()) part works.
For example:
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //liest die namen
}
}
This would print me every name after name. But when I change the table, the while loop ends after that. (no error, the program just finishes)
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //writes the name
//look, if name is in Arraylist "namelist"). if yes, than write the matching date from "timelist" into the database.
if (namelist.contains(name)){
System.out.println("name found: "+ name);
int listIndizi = namelist.indexOf(name); //get index
Long indiziDatum = (long) timelist.get(listIndizi); //get date from same Index
System.out.println(indiziDatum); // print date so i can see it is correct (which it is)
statement.executeUpdate("UPDATE users SET follows_date ="+ indiziDatum +" WHERE username = '"+name+"'"); //updates the follows_date column
}
}
Everything works fine, except that now, the while loop doesn't continues after the first passage, but ends.
The resultSet of a statement is closed and will not return further results if you execute another statement. Create a new separate statement object for the update and everything should work as excepted.
Statement statement1 = connection.createStatement();
Statement statement2 = connection.createStatement();
ResultSet resultSet1 = statement1.executeQuery("SELECT username FROM users");
while(resultSet1.next()){
...
statement2.executeUpdate("UPDATE users ..."));
}
As to Why it happens:
Here is the explanation from the official documentation:
A ResultSet object is automatically closed when the Statement object that generated it is closed, re-executed, or used to retrieve the next result from a sequence of multiple results.
Alternative Approach:
From your sample, it seems you are trying to update the "same" row in your resultSet, you should consider using an Updatable ResultSet.
Sample code from the official documentation:
public void modifyPrices(float percentage) throws SQLException {
Statement stmt = null;
try {
stmt = con.createStatement();
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = stmt.executeQuery(
"SELECT * FROM " + dbName + ".COFFEES");
while (uprs.next()) {
float f = uprs.getFloat("PRICE");
uprs.updateFloat( "PRICE", f * percentage);
uprs.updateRow();
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
} finally {
if (stmt != null) { stmt.close(); }
}
}
I'm trying to execute a prepared statement in JDBC, and everytime I execute it I get the error message "Paramater not set".
I have tried repeatedly to check for unset parameters - but I only have the one. This leads me to believe it is another foolish error on my part.
If you could point this out to me, I would be very grateful
public book search(String key){
book temp = null;
try {
String stmt = "SELECT BookID, Title, Author, Media, Available FROM BOOK WHERE Title LIKE ?;";
connection = DatabaseConnection();
PreparedStatement preparedStmt = connection.prepareStatement(stmt);
System.out.println(key);
preparedStmt.setObject(1, key);//the name
statement = connection.prepareStatement(stmt); //Using Prepared Statements prepare the query
resultSet = statement.executeQuery(); //Execute the query
while (resultSet.next()) {
int bookID = resultSet.getInt("BookID");//Get the userName
String title = resultSet.getString("Title"); //Get the score
String author = resultSet.getString("Author"); //Get the score
String media = resultSet.getString("Media"); //Get the score
boolean available = resultSet.getBoolean("Available"); //Get the score
temp = new book(title,author,media,available,bookID);
}
connection.close(); //close connection
} catch (SQLException e) {
System.err.println("Got an exception!");
System.err.println(e.getMessage());
}
return temp;
}
You're calling prepareStatement twice, setting the parameter on the first one but then calling executeQuery on the second.
It's not clear where you're event declaring statement or resultSet, but you want:
PreparedStatement preparedStmt = connection.prepareStatement(stmt);
preparedStmt.setString(1, key);
ResultSet resultSet = preparedStmt.executeQuery();
Note that I've made resultSet a local variable - you really don't want it to be a field... there's also no reason for your temp variable as you can just return directly from the while loop. (I've changed the code to use setString instead of setObject, too...)
You should use try-with-resources statements to close both the statement and the result set automatically...)
I am running the code, however am getting a "Invalid state, the ResultSet object is closed." error. What is causing the error?
try{
query = "SELECT * FROM BUNDLE_TEMP "
+ "MINUS "
+ "SELECT * FROM BUNDLE";
rs = stmt.executeQuery(query);
while (rs.next()){
String bundle = rs.getString("BUNDLE");
String week = rs.getString("WEEK");
String sched_dt = rs.getString("SCHED_DT").replace(" 00:00:00.0", "");
String dropper_id = rs.getString("DROPPER_ID");
query = "INSERT INTO BUNDLE "
+ "VALUES ('"
+ bundle+"','"
+ week+"','"
+ sched_dt+"','"
+ dropper_id+"')";
stmt.executeUpdate(query);
}
}catch(Exception e){
System.out.println("Error while trying to insert into BUNDLE\n"+query+"\n"+ e);
}
You cannot execute another SQL query on the same Statement you're currently iterating over with a ResultSet. Doing this will close the previously open cursor (your SELECT query resp. ResultSet):
To quote the API docs for Statement:
By default, only one ResultSet object per Statement object can be open
at the same time. Therefore, if the reading of one ResultSet object is
interleaved with the reading of another, each must have been generated
by different Statement objects. All execution methods in the Statement
interface implicitly close a statment's current ResultSet object if an
open one exists.
Create another Statement instance from your Connection, let's call it updateStmt and executeUpdate() on that one.
Also, look into Prepared Statements for your update, it will probably be more performant and secure.
This question already has answers here:
ResultSet exception - before start of result set
(6 answers)
Closed 5 years ago.
try
{
PreparedStatement s = (PreparedStatement) conn.prepareStatement("SELECT voters.Check,count(*) FROM voting.voters where FirstName="+first+"and LastName="+last+" and SSN="+voter_ID);
//java.sql.Statement k = conn.createStatement();
rs=s.executeQuery();
//s.executeQuery("SELECT voters.Check,count(*) FROM voting.voters where FirstName="+first+"and LastName="+last+" and SSN="+voter_ID);
System.out.println(rs.first());
c=rs.getInt(1);
d=rs.getInt(2);
System.out.println(c);
System.out.println(d);
if(c==1 && d==1)
{
s.executeUpdate("update cand set total=total+1 where ssn="+can_ID);
System.out.println("Succeful vote");
System.out.println("after vote");
s.executeUpdate("update voters set voters.Check=1 where ssn="+voter_ID);
toclient=1;
PreparedStatement qw = (PreparedStatement) conn.prepareStatement("select FirstName from cand where ssn="+can_ID);
// rs=k.executeQuery("select FirstName from cand where ssn="+can_ID);
rs1 = qw.executeQuery();//Error Here Plz help me
String name1= (String) rs1.getString(1);
System.out.println(name1);
s.executeUpdate("update voters set VTO="+name1+"where ssn="+voter_ID);
System.out.println(rs.getString(1));
}
else
{
if(c != -1)
toclient =2;
if( d ==0)
toclient =3;
if( d>1)
toclient =4;
}
System.out.println("out-----------");
rs.close();
s.close();
}
catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Error IS :
java.sql.SQLException: Before start of result set
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1072)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:986)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:981)
The common practice is to use rs.next() method with while cycle:
PreparedStatement st = conn.prepareStatement("select 1 from mytable");
ResultSet rs = st.executeQuery();
while (rs.next()) {
// do something with result set
}
rs.close();
st.close();
I've omitted try/catch/finally clauses for clarity. Note that you should invoke each close() method in separate finally block.
While rs1.first() may work, to avoid exception I would like to avoid it and use rs1.next() instead.
See javadoc of ResultSet.first():
SQLException - if a database access error occurs; this method is called on a closed result set or the result set type is TYPE_FORWARD_ONLY
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
while next doesn't have this limitation
Code:
if (rs1.next()) {
String name1 = rs1.getString(1);
}
Tips: avoid useless type casting (your code is full of them)
In your code snippet you create PreparedStatements but you do not use them correctly. Prepared statements are meant to be used as a kind of 'statement template' which is bound to values before it executes. To quote the javadoc:
PreparedStatement pstmt = con.prepareStatement(
"UPDATE EMPLOYEES SET SALARY = ? WHERE ID = ?");
pstmt.setBigDecimal(1, 153833.00)
pstmt.setInt(2, 110592)
This has two big advantages over your current usage of PreparedStatement:
one PreparedStatement can be used for multiple executes
it prevents a possible SQL injection attack
The second one here is the biggie, if for instance your variables first and last are collected in a user interface and not reformatted, you run the risk of parts of SQL being input for those values, which then end up in your statements! Using bound parameters they will just be used as values, not part of the SQL statement.
When you get a resultset, the cursor is placed before the first row. Trying to get anything before moving your cursor to the first row will cause the error you received. You need to move the cursor to the first row using this line:
rs1.first();
before calling
String name1 = (String) rs1.getString(1);
Of course, make sure the resultset contains entries before calling rs1.getString(1).
Call rs1.first() before using the ResultSet.
Moves the cursor to the first row in this ResultSet object.
Initially the cursor position of the ResultSet is before the start of the set. The first() method returns true if there is data in the set. So preferably:
if (rs1.first()) {
String name1 = (String) rs1.getString(1);
}
So, to be sure the proper use of PreparedStatment, here is your original example adjusted for best practices (note the cast is redundant):
PreparedStatement s = conn.prepareStatement(
"SELECT voters.Check,count(*) " +
"FROM voting.voters " +
"where FirstName=? and LastName=? and SSN=?");
s.setString(1,first);
s.setString(2,last);
s.setString(3,voter_ID);
ResultSet rs = s.executeQuery();
while( rs.next() ) {
c = rs.getInt(1);
d = rs.getInt(2);
}
Hope this helps... :)