Storing Result set into an array

Storing Result set into an array - java

i know this should be simpel and im probably staring straight at the problem but once again im stuck and need the help of the code gurus.
im trying too take one row from a column in jdbc, and put them in an array.
i do this as follows:
public void fillContactList()
{
createConnection();
try
{
Statement stmt = conn.createStatement();
ResultSet namesList = stmt.executeQuery("SELECT name FROM Users");
try
{
while (namesList.next())
{
contactListNames[1] = namesList.getString(1);
System.out.println("" + contactListNames[1]);
}
}
catch(SQLException q)
{
}
conn.commit();
stmt.close();
conn.close();
}
catch(SQLException e)
{
}
creatConnection is an already defined method that does what it obviously does.
i creat my result set
while theres another one,
i store the string of that column into an array.
then print it out for good measure. too make sure its there.
the problem is that its storing the entire column into contactListNames[1]
i wanted to make it store column1 row 1 into [1]
then column 1 row 2 into [2]
i know i could do this with a loop. but i dont know too take only one row at a time from a single column. any ideas?
p.s ive read the api, i jsut cant see anything that fits.

You should use an ArrayList which provides all the logic to automatically extend the array.
List rowValues = new ArrayList();
while (namesList.next()) {
rowValues.add(namesList.getString(1));
}
// You can then put this back into an array if necessary
contactListNames = (String[]) rowValues.toArray(new String[rowValues.size()]);

Did you mean something like:
int i = 0;
ResultSet rs = stmt.executeQuery("select name from users");
while (rs.next()) {
String name = rs.getString("name");
names[i++] = name;
}

Related

Java SE8 JDBC trouble [duplicate]

I'm trying to create a simple method that receives a ResultSet as a parameter and returns an int that contains the row count of the ResultSet. Is this a valid way of doing this or not so much?
int size = 0;
try {
while(rs.next()){
size++;
}
}
catch(Exception ex) {
System.out.println("------------------Tablerize.getRowCount-----------------");
System.out.println("Cannot get resultSet row count: " + ex);
System.out.println("--------------------------------------------------------");
}
I tried this:
int size = 0;
try {
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(Exception ex) {
return 0;
}
return size;
But I got an error saying
com.microsoft.sqlserver.jdbc.SQLServerException:
The requested operation is not supported on forward only result sets.

If you have access to the prepared statement that results in this resultset, you can use
connection.prepareStatement(sql,
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
This prepares your statement in a way that you can rewind the cursor. This is also documented in the ResultSet Javadoc
In general, however, forwarding and rewinding cursors may be quite inefficient for large result sets. Another option in SQL Server would be to calculate the total number of rows directly in your SQL statement:
SELECT my_table.*, count(*) over () total_rows
FROM my_table
WHERE ...

Statement s = cd.createStatement();
ResultSet r = s.executeQuery("SELECT COUNT(*) AS recordCount FROM FieldMaster");
r.next();
int count = r.getInt("recordCount");
r.close();
System.out.println("MyTable has " + count + " row(s).");
Sometimes JDBC does not support following method gives Error like `TYPE_FORWARD_ONLY' use this solution
Sqlite does not support in JDBC.
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
So at that time use this solution.

your sql Statement creating code may be like
statement = connection.createStatement();
To solve "com.microsoft.sqlserver.jdbc.SQLServerException: The requested operation is not supported on forward only result sets" exception, change above code with
statement = connection.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
After above change you can use
int size = 0;
try {
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(Exception ex) {
return 0;
}
return size;
to get row count

I just made a getter method.
public int getNumberRows(){
try{
statement = connection.creatStatement();
resultset = statement.executeQuery("your query here");
if(resultset.last()){
return resultset.getRow();
} else {
return 0; //just cus I like to always do some kinda else statement.
}
} catch (Exception e){
System.out.println("Error getting row count");
e.printStackTrace();
}
return 0;
}

Do a SELECT COUNT(*) FROM ... query instead.

Most drivers support forward only resultset - so method like last, beforeFirst etc are not supported.
The first approach is suitable if you are also getting the data in the same loop - otherwise the resultSet has already been iterated and can not be used again.
In most cases the requirement is to get the number of rows a query would return without fetching the rows. Iterating through the result set to find the row count is almost same as processing the data. It is better to do another count(*) query instead.

If you have table and are storing the ID as primary and auto increment then this will work
Example code to get the total row count http://www.java2s.com/Tutorial/Java/0340__Database/GettheNumberofRowsinaDatabaseTable.htm
Below is code
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class Main {
public static void main(String[] args) throws Exception {
Connection conn = getConnection();
Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
st.executeUpdate("create table survey (id int,name varchar(30));");
st.executeUpdate("insert into survey (id,name ) values (1,'nameValue')");
st.executeUpdate("insert into survey (id,name ) values (2,null)");
st.executeUpdate("insert into survey (id,name ) values (3,'Tom')");
st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT * FROM survey");
rs = st.executeQuery("SELECT COUNT(*) FROM survey");
// get the number of rows from the result set
rs.next();
int rowCount = rs.getInt(1);
System.out.println(rowCount);
rs.close();
st.close();
conn.close();
}
private static Connection getConnection() throws Exception {
Class.forName("org.hsqldb.jdbcDriver");
String url = "jdbc:hsqldb:mem:data/tutorial";
return DriverManager.getConnection(url, "sa", "");
}
}

Your function will return the size of a ResultSet, but its cursor will be set after last record, so without rewinding it by calling beforeFirst(), first() or previous() you won't be able to read its rows, and rewinding methods won't work with forward only ResultSet (you'll get the same exception you're getting in your second code fragment).

Others have already answered how to solve your problem, so I won't repeat what has already been said, but I will says this: you should probably figure out a way to solve your problems without knowing the result set count prior to reading through the results.
There are very few circumstances where the row count is actually needed prior to reading the result set, especially in a language like Java. The only case I think of where a row count would be necessary is when the row count is the only data you need(in which case a count query would be superior). Otherwise, you are better off using a wrapper object to represent your table data, and storing these objects in a dynamic container such as an ArrayList. Then, once the result set has been iterated over, you can get the array list count. For every solution that requires knowing the row count before reading the result set, you can probably think of a solution that does so without knowing the row count before reading without much effort. By thinking of solutions that bypass the need to know the row count before processing, you save the ResultSet the trouble of scrolling to the end of the result set, then back to the beginning (which can be a VERY expensive operation for large result sets).
Now of course I'm not saying there are never situations where you may need the row count before reading a result set. I'm just saying that in most circumstances, when people think they need the result set count prior to reading it, they probably don't, and it's worth taking 5 minutes to think about whether there is another way.
Just wanted to offer my 2 cents on the topic.

Following two options worked for me:
1) A function that returns the number of rows in your ResultSet.
private int resultSetCount(ResultSet resultSet) throws SQLException{
try{
int i = 0;
while (resultSet.next()) {
i++;
}
return i;
} catch (Exception e){
System.out.println("Error getting row count");
e.printStackTrace();
}
return 0;
}
2) Create a second SQL statement with the COUNT option.

The ResultSet has it's methods that move the Cursor back and forth depending on the option provided. By default, it's forward moving(TYPE_FORWARD_ONLY ResultSet type).
Unless CONSTANTS indicating Scrollability and Update of ResultSet properly, you might end up getting an error.
E.g. beforeLast()
This method has no effect if the result set contains no rows.
Throws Error if it's not TYPE_FORWARD_ONLY.
The best way to check if empty rows got fetched --- Just to insert new record after checking non-existence
if( rs.next() ) {
Do nothing
} else {
No records fetched!
}
See here

Here's some code that avoids getting the count to instantiate an array, but uses an ArrayList instead and just before returning converts the ArrayList to the needed array type.
Note that Supervisor class here implements ISupervisor interface, but in Java you can't cast from object[] (that ArrayList's plain toArray() method returns) to ISupervisor[] (as I think you are able to do in C#), so you have to iterate through all list items and populate the result array.
/**
* Get Supervisors for given program id
* #param connection
* #param programId
* #return ISupervisor[]
* #throws SQLException
*/
public static ISupervisor[] getSupervisors(Connection connection, String programId)
throws SQLException
{
ArrayList supervisors = new ArrayList();
PreparedStatement statement = connection.prepareStatement(SQL.GET_SUPERVISORS);
try {
statement.setString(SQL.GET_SUPERVISORS_PARAM_PROGRAMID, programId);
ResultSet resultSet = statement.executeQuery();
if (resultSet != null) {
while (resultSet.next()) {
Supervisor s = new Supervisor();
s.setId(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ID));
s.setFirstName(resultSet.getString(SQL.GET_SUPERVISORS_RESULT_FIRSTNAME));
s.setLastName(resultSet.getString(SQL.GET_SUPERVISORS_RESULT_LASTNAME));
s.setAssignmentCount(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ASSIGNMENT_COUNT));
s.setAssignment2Count(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ASSIGNMENT2_COUNT));
supervisors.add(s);
}
resultSet.close();
}
} finally {
statement.close();
}
int count = supervisors.size();
ISupervisor[] result = new ISupervisor[count];
for (int i=0; i<count; i++)
result[i] = (ISupervisor)supervisors.get(i);
return result;
}

From http://docs.oracle.com/javase/1.4.2/docs/api/java/sql/ResultSetMetaData.html
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
A ResultSet contains metadata which gives the number of rows.

Prepare statement inside a loop

I trying execute a query inside a loop.I am tryning this code :
public List<Products> DisplayProducts(String []a)
{
ResultSet rs = null;
List<Products> Data=null;
try
{
for(int i=0;i<a.length;i++)
{
String query = "select * from products where Brand=?";
PreparedStatement stmt=DataBaseConnection.DBConn.getConnection().prepareStatement(query);
stmt.setString(1, a[i]);
rs=stmt.executeQuery();
}
if(rs.next())
{
rs.beforeFirst();
Data=new ArrayList<Products>();
while(rs.next())
{
Products p=new Products();
p.setTitle(rs.getString(2));
p.setCategory(rs.getString(3));
p.setSubCategory(rs.getString(4));
p.setSubCategoryTwo(rs.getString(5));
p.setPrice(rs.getInt(6));
p.setFlavour(rs.getString(7));
p.setImage(rs.getString(8));
p.setBrand(rs.getString(9));
p.setInstock(rs.getString(10));
p.setInstockQty(rs.getInt(11));
Data.add(p);
}
}
return Data;
}
catch(Exception e)
{
System.out.println(e.getStackTrace());
return null;
}
}
I have a jsp page where I have Checkboxes and I am displaying multiple products on this page. I am sorting this products by BRANDS. User selects Brand by checking checkbox.
I am passing the value of checkbox to a servlet and on that servlet calling function Display Products:
String arr[]=request.getParameterValues("On");
List<Products> Data=new SessionBeanClass().DisplayProducts(arr);
Please tell me how do I execute this and get the result ?

I suppose you need to return the list of all products with the checkbox ticked. In that case i suppose you have a logic error here. This method only returns the last Product record.
Instead of looping through different id you could use 'IN' clause and return all at once. There are many differet ways to achieve IN clause. The one given below is a simple alternative. You could check for various operations in http://www.journaldev.com/2521/jdbc-preparedstatement-in-clause-alternative-approaches or http://www.javaranch.com/journal/200510/Journal200510.jsp#a2
In addition to that try following java naming conventions and clean up connections using finally
Try
public List<Products> DisplayProducts(String[] a) {
ResultSet rs;
List<Products> data;
PreparedStatement stmt;
try {
StringBuilder param = new StringBuilder();
for(String str : a){
param.append("'").append(str).append("', ");
}
String query = "select * from products where Brand in (" + param.substring(0, param.length() - 2) + ")";
stmt = DataBaseConnection.DBConn.getConnection().prepareStatement(query);
rs = stmt.executeQuery();
if (rs != null) {
data = new ArrayList<Products>();
while (rs.next()) {
Products p = new Products();
p.setTitle(rs.getString(2));
p.setCategory(rs.getString(3));
p.setSubCategory(rs.getString(4));
p.setSubCategoryTwo(rs.getString(5));
p.setPrice(rs.getInt(6));
p.setFlavour(rs.getString(7));
p.setImage(rs.getString(8));
p.setBrand(rs.getString(9));
p.setInstock(rs.getString(10));
p.setInstockQty(rs.getInt(11));
data.add(p);
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
stmt.close();
}
return data;
}
Explanation as per comment
Ok. I suppose your idea here is to pass a set of brand names say adidas, nike, etc.. and select all the product details. So you need to do something like select * from products where Brand in ('adidas', 'nike'). This will give you all the products. So for this you pass the selected brand names as a string array. So what i did was to get the values from array and format it and make it as argument for IN clause. So of IN clause it needs comma separated values. Since its a Sting we need to give single quote ' as well. So from an array [adidas, nike] i need to construct 'adidas', 'nike'. That is what done in the for loop, appending ' and , (comma). So after for loop we'll have an additional comma and space at the end (e.g. 'adidas', 'nike', ). In order to remove this i remove the last two charaters by taking substring as param.substring(0, param.length() - 2). This is fed to the query and retrieve the result.

MySQL: Out of range, but the column isn't last?

After an awful lot of time figuring out what's wrong with my code, I decided to go ahead and ask for help. As of right now this is the code which's causing the error:
try {
ResultSet rs = statement.executeQuery("SELECT `message` FROM `notifications` WHERE `active`='1'");
List<String> messages = new ArrayList<String>();
int index = 1;
if (rs.next()) {
while (!rs.isLast()) {
messages.add(rs.getString(index));
index ++;
}
if (rs.isLast()) {
messages.add(rs.getString(index));
}
}
return messages.toArray(new String[messages.size()]);
} catch (Exception localException) {
if (localException instanceof NullPointerException) {
/* ignore for now */
localException.printStackTrace();
} else {
localException.printStackTrace();
}
}
The error is telling me that the column is out of range, but when I look into my database it's not.
java.sql.SQLException: Column Index out of range, 2 > 1.
Any suggestions? Thanks in advance!

Inside the
if (rs.isLast()) {
messages.add(rs.getString(index));
}
The index will be 2, in this statement, but your resultSet only contains one column.
When you say rs.getString(2) it is going to grab the value associated with the 2nd column.
Should be :
ResultSet rs = statement.executeQuery("SELECT `message` FROM `notifications` WHERE `active`='1'");
List<String> messages = new ArrayList<String>();
int index = 1;
while (rs.next()) {
messages.add(rs.getString(index));
}
Note: A best practice is to get the value based on column name instead of index. I believe you thought that getString(index) accessed the row, and calling it by the column name would clear that up for you.
ResultSet rs = statement.executeQuery("SELECT `message` FROM `notifications` WHERE `active`='1'");
List<String> messages = new ArrayList<String>();
String column = "message";
while (rs.next()) {
messages.add(rs.getString(column));
}

The isLast method only determines if you're on the last row, not the last column. The way that you're using index is to iterate over all columns on the same row.
The way to determine the number of columns is to get the ResultSetMetaData object from the ResultSet and get the number of columns from it, using the getMetaData() method on the ResultSet and the getColumnCount() method on the ResultSetMetaData. Then you can use that to loop through your columns.

In your query you have just one column message in the SELECT clause. Remove index++ from your java code to get rid of the exception because rs.getString(index) is trying to get value of column number 2 which does not exists in the query result.

How to get row count using ResultSet in Java?

I'm trying to create a simple method that receives a ResultSet as a parameter and returns an int that contains the row count of the ResultSet. Is this a valid way of doing this or not so much?
int size = 0;
try {
while(rs.next()){
size++;
}
}
catch(Exception ex) {
System.out.println("------------------Tablerize.getRowCount-----------------");
System.out.println("Cannot get resultSet row count: " + ex);
System.out.println("--------------------------------------------------------");
}
I tried this:
int size = 0;
try {
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(Exception ex) {
return 0;
}
return size;
But I got an error saying
com.microsoft.sqlserver.jdbc.SQLServerException:
The requested operation is not supported on forward only result sets.

If you have access to the prepared statement that results in this resultset, you can use
connection.prepareStatement(sql,
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
This prepares your statement in a way that you can rewind the cursor. This is also documented in the ResultSet Javadoc
In general, however, forwarding and rewinding cursors may be quite inefficient for large result sets. Another option in SQL Server would be to calculate the total number of rows directly in your SQL statement:
SELECT my_table.*, count(*) over () total_rows
FROM my_table
WHERE ...

Statement s = cd.createStatement();
ResultSet r = s.executeQuery("SELECT COUNT(*) AS recordCount FROM FieldMaster");
r.next();
int count = r.getInt("recordCount");
r.close();
System.out.println("MyTable has " + count + " row(s).");
Sometimes JDBC does not support following method gives Error like `TYPE_FORWARD_ONLY' use this solution
Sqlite does not support in JDBC.
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
So at that time use this solution.

your sql Statement creating code may be like
statement = connection.createStatement();
To solve "com.microsoft.sqlserver.jdbc.SQLServerException: The requested operation is not supported on forward only result sets" exception, change above code with
statement = connection.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
After above change you can use
int size = 0;
try {
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(Exception ex) {
return 0;
}
return size;
to get row count

I just made a getter method.
public int getNumberRows(){
try{
statement = connection.creatStatement();
resultset = statement.executeQuery("your query here");
if(resultset.last()){
return resultset.getRow();
} else {
return 0; //just cus I like to always do some kinda else statement.
}
} catch (Exception e){
System.out.println("Error getting row count");
e.printStackTrace();
}
return 0;
}

Do a SELECT COUNT(*) FROM ... query instead.

Most drivers support forward only resultset - so method like last, beforeFirst etc are not supported.
The first approach is suitable if you are also getting the data in the same loop - otherwise the resultSet has already been iterated and can not be used again.
In most cases the requirement is to get the number of rows a query would return without fetching the rows. Iterating through the result set to find the row count is almost same as processing the data. It is better to do another count(*) query instead.

If you have table and are storing the ID as primary and auto increment then this will work
Example code to get the total row count http://www.java2s.com/Tutorial/Java/0340__Database/GettheNumberofRowsinaDatabaseTable.htm
Below is code
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class Main {
public static void main(String[] args) throws Exception {
Connection conn = getConnection();
Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
st.executeUpdate("create table survey (id int,name varchar(30));");
st.executeUpdate("insert into survey (id,name ) values (1,'nameValue')");
st.executeUpdate("insert into survey (id,name ) values (2,null)");
st.executeUpdate("insert into survey (id,name ) values (3,'Tom')");
st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT * FROM survey");
rs = st.executeQuery("SELECT COUNT(*) FROM survey");
// get the number of rows from the result set
rs.next();
int rowCount = rs.getInt(1);
System.out.println(rowCount);
rs.close();
st.close();
conn.close();
}
private static Connection getConnection() throws Exception {
Class.forName("org.hsqldb.jdbcDriver");
String url = "jdbc:hsqldb:mem:data/tutorial";
return DriverManager.getConnection(url, "sa", "");
}
}

Your function will return the size of a ResultSet, but its cursor will be set after last record, so without rewinding it by calling beforeFirst(), first() or previous() you won't be able to read its rows, and rewinding methods won't work with forward only ResultSet (you'll get the same exception you're getting in your second code fragment).

Following two options worked for me:
1) A function that returns the number of rows in your ResultSet.
private int resultSetCount(ResultSet resultSet) throws SQLException{
try{
int i = 0;
while (resultSet.next()) {
i++;
}
return i;
} catch (Exception e){
System.out.println("Error getting row count");
e.printStackTrace();
}
return 0;
}
2) Create a second SQL statement with the COUNT option.

The ResultSet has it's methods that move the Cursor back and forth depending on the option provided. By default, it's forward moving(TYPE_FORWARD_ONLY ResultSet type).
Unless CONSTANTS indicating Scrollability and Update of ResultSet properly, you might end up getting an error.
E.g. beforeLast()
This method has no effect if the result set contains no rows.
Throws Error if it's not TYPE_FORWARD_ONLY.
The best way to check if empty rows got fetched --- Just to insert new record after checking non-existence
if( rs.next() ) {
Do nothing
} else {
No records fetched!
}
See here

Here's some code that avoids getting the count to instantiate an array, but uses an ArrayList instead and just before returning converts the ArrayList to the needed array type.
Note that Supervisor class here implements ISupervisor interface, but in Java you can't cast from object[] (that ArrayList's plain toArray() method returns) to ISupervisor[] (as I think you are able to do in C#), so you have to iterate through all list items and populate the result array.
/**
* Get Supervisors for given program id
* #param connection
* #param programId
* #return ISupervisor[]
* #throws SQLException
*/
public static ISupervisor[] getSupervisors(Connection connection, String programId)
throws SQLException
{
ArrayList supervisors = new ArrayList();
PreparedStatement statement = connection.prepareStatement(SQL.GET_SUPERVISORS);
try {
statement.setString(SQL.GET_SUPERVISORS_PARAM_PROGRAMID, programId);
ResultSet resultSet = statement.executeQuery();
if (resultSet != null) {
while (resultSet.next()) {
Supervisor s = new Supervisor();
s.setId(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ID));
s.setFirstName(resultSet.getString(SQL.GET_SUPERVISORS_RESULT_FIRSTNAME));
s.setLastName(resultSet.getString(SQL.GET_SUPERVISORS_RESULT_LASTNAME));
s.setAssignmentCount(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ASSIGNMENT_COUNT));
s.setAssignment2Count(resultSet.getInt(SQL.GET_SUPERVISORS_RESULT_ASSIGNMENT2_COUNT));
supervisors.add(s);
}
resultSet.close();
}
} finally {
statement.close();
}
int count = supervisors.size();
ISupervisor[] result = new ISupervisor[count];
for (int i=0; i<count; i++)
result[i] = (ISupervisor)supervisors.get(i);
return result;
}

From http://docs.oracle.com/javase/1.4.2/docs/api/java/sql/ResultSetMetaData.html
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
A ResultSet contains metadata which gives the number of rows.

How to check if resultset has one row or more?

How to check if resultset has one row or more with JDBC?

ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");
boolean isMoreThanOneRow = rs.first() && rs.next();
You didn't ask this one, but you may need it:
boolean isEmpty = ! rs.first();
Normally, we don't need the row count because we use a WHILE loop to iterate through the result set instead of a FOR loop:
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");
while (rs.next()) {
// retrieve and print the values for the current row
int i = rs.getInt("a");
String s = rs.getString("b");
float f = rs.getFloat("c");
System.out.println("ROW = " + i + " " + s + " " + f);
}
However, in some cases, you might want to window the results, and you need the record count ahead of time to display to the user something like Row 1 to 10 of 100. You can do a separate query with SELECT COUNT(*) first, to get the record count, but note that the count is only approximate, since rows can be added or removed between the time it takes to execute the two queries.
Sample from ResultSet Overview

There are many options, and since you don't provide more context the only thing left is to guess. My answers are sorted by complexity and performance ascending order.
Just run select count(1) FROM ... and get the answer. You'd have to run another query that actually selects and returns the data.
Iterate with rs.next() and count until you're happy. Then if you still need the actual data re-run same query.
If your driver supports backwards iteration, go for rs.next() couple of times and then rewind back with rs.previous().

You don't need JDBC for this. The normal idiom is to collect all results in a collection and make use of the collection methods, such as List#size().
List<Item> items = itemDAO.list();
if (items.isEmpty()) {
// It is empty!
if (items.size() == 1) {
// It has only one row!
} else {
// It has more than one row!
}
where the list() method look like something:
public List<Item> list() throws SQLException {
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
List<Item> items = new ArrayList<Item>();
try {
connection = database.getConnection();
statement = connection.createStatement();
resultSet = statement.executeQuery(SQL_LIST);
while (resultSet.next()) {
Item item = new Item();
item.setId(resultSet.getLong("id"));
item.setName(resultSet.getString("name"));
// ...
items.add(item);
}
} finally {
if (resultSet != null) try { resultSet.close(); } catch (SQLException logOrIgnore) {}
if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
if (connection != null) try { connection.close(); } catch (SQLException logOrIgnore) {}
}
return items;
}

If you want to make sure that there is exactly one row, you can ensure that the first row is the last:
ResultSet rs = stmt.executeQuery("SELECT a FROM Table1 WHERE b=10");
if (rs.isBeforeFirst() && rs.next() && rs.isFirst() && rs.isLast()) {
// Logic for where there's exactly 1 row
Long valA = rs.getLong("a");
// ...
}
else {
// More that one row or 0 rows returned.
// ..
}

My no-brainer suggestion: Fetch the first result row, and then try to fetch the next. If the attempt is successful, you have more than one row.
If there is more than one row and you want to process that data, you'll need to either cache the stuff from the first row, or use a scrollable result set so you can seek back to the top before going through the results.
You can also ask SQL directly for this information by doing a SELECT COUNT(*) on the rest of your query; the result will be 0, 1 or more depending on how many rows the rest of the query would return. That's pretty easy to implement but involves two queries to the DB, assuming you're going to want to read and process the actual query next.

This implementation allows you to check for whether result of the query is empty or not at the cost of duplicating some lines.
ResultSet result = stmt.executeQuery("SELECT * FROM Table");
if(result.next()) {
// Duplicate the code which should be pasted inside while
System.out.println(result.getInt(1));
System.out.println(result.getString(2));
while(result.next()){
System.out.println(result.getInt(1));
System.out.println(result.getString(2));
}
}else{
System.out.println("Query result is empty");
}
Drawbacks:
In this implementation a portion of the code will be duplicated.
You cannot know how many lines are present in the result.

Get the Row Count using ResultSetMetaData class.
From your code u can create ResultSetMetaData like :
ResultSetMetaData rsmd = resultSet.getMetaData(); //get ResultSetMetaData
rsmd.getColumnCount(); // get row count from resultsetmetadata

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