Develop Reference

get column values into an array

I have a database table with columns : name, residence, contact. and I want to retrieve only the values in the 'contact column' into an array. the following code is what I wrote:
List l = new ArrayList();
try {
String sql = "select * from members";
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
while (rs.next()) {
String con = rs.getString("Contact");
l.add(con);
System.out.println(l);
}
} catch (Exception e) {
e.getMessage();
}
but this generates the following result:
[0547615632]
[0547615632, 0246687643]
[0547615632, 0246687643, 0558581764]
whilst I have only 3 records in the table and each having a contact value.
please how do I write the code so that I can get only a single array displaying the result like this:
[0547615632, 0246687643, 0558581764]
thank you very much.

You should move the print command out of the while loop:
List l = new ArrayList();
try {
String sql = "select * from members";
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
while (rs.next()) {
String con = rs.getString("Contact");
l.add(con);
}
} catch (Exception e) {
e.getMessage();
}
System.out.println(l);
OR only print the current element in each iteration;
List l = new ArrayList();
try {
String sql = "select * from members";
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
while (rs.next()) {
String con = rs.getString("Contact");
l.add(con);
System.out.print(con + " ");
}
} catch (Exception e) {
e.getMessage();
}

how to insert object to h2

I've read H2 docs about storing objects in database. There is special SQL type OTHER and methods setObject and getObject. I've tried this code:
PreparedStatement statement = null;
try {
statement = connection.prepareStatement("CREATE TABLE PUBLIC.foo (name VARCHAR(64) NOT NULL, data OTHER NULL);");
statement.execute();
} finally {
statement.close();
}
statement = null;
try {
statement = connection.prepareStatement("INSERT INTO PUBLIC.foo (name, data) VALUES(?,?);");
statement.setString(1, "lololo");
statement.setObject(2, new String[]{"foo", "bar"});
statement.execute();
}finally {
statement.close();
}
But I've got the exception:
org.h2.jdbc.JdbcSQLException: Ше�тнадцатирична� �трока �одержит неше�тнадцатиричные �имволы: "(foo, bar)"
Hexadecimal string contains non-hex character: "(foo, bar)"; SQL statement:
INSERT INTO PUBLIC.foo (name, data) VALUES(?,?) -- (?1, ?2) [90004-191]
What is wrong?

I believe this is what you were look for (Even I was).
You just need to create a column in your table with type as 'other'.
See 'create table testobj2(obj other)'
Look at my Sample code :
static String DB_DRIVER = "org.h2.Driver";
static String DB_CONNECTION = "jdbc:h2:./test2";
static String DB_USER = "";
static String DB_PASSWORD = "";
public static void benchmarkH2Inserts() {
try {
Class.forName(DB_DRIVER);
Connection dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER, DB_PASSWORD);
String createQry = "create table testobj2(obj other)";
String insertQuery = "insert into testobj2(obj) values(?)";
String selectQuery = "select * from testobj2";
// dbConnection.setAutoCommit(false);
dbConnection.prepareStatement(createQry).executeUpdate();
long lStartTime = System.nanoTime();
for(int i=0; i<10000; i++) {
dbConnection.setAutoCommit(false);
CloudElement_Circuit obj = new CloudElement_Circuit();
obj.setNrm8DesignId(1230L);
PreparedStatement preparedStatement = dbConnection.prepareStatement(insertQuery);
preparedStatement.setObject(1,obj);
preparedStatement.execute();
dbConnection.commit();
}
long lEndTime = System.nanoTime();
long output = lEndTime - lStartTime;
System.out.println("benchmarkH2Inserts() : Elapsed time in nanoseconds: " + output);
System.out.println("benchmarkH2Inserts() : Elapsed time in milliseconds: " + output / 1000000);
//Selecting
PreparedStatement preparedStatement = dbConnection.prepareStatement(selectQuery);
ResultSet rs = preparedStatement.executeQuery();
while(rs.next()) {
CloudElement_Circuit obj = (CloudElement_Circuit) rs.getObject("obj");
System.out.println("Fetched Object : " + obj.getNrm8DesignId());
}
dbConnection.close();
} catch (Exception e) {
e.printStackTrace();
}
}
Note that 'CloudElement_Circuit' is a Serialized class.
Look at 'OTHER Type' here : http://www.h2database.com/html/datatypes.html
H2 Example : https://www.javatips.net/blog/h2-database-example

Try this approach
List<String> genre = new ArrayList<String>();
String comma="";
StringBuilder allGenres = new StringBuilder();
for (String g: genre) {
allGenres.append(comma);
allGenres.append(g);
comma = ", ";
}
Then you can pass it like this
preparedStmt.setString (2, allGenres.toString());

How to insert values from csv into database in java

I have tried the following code to split the csv values and now how do insert it in to DB? Do I have save the values in to separate variables to match column names? I am unable to figure out.
Note: I don't want to use any csv parser right now. I just want to do it manually
public static void main(String[] args) throws IOException, ClassNotFoundException, SQLException {
String name;
String email;
String phone;
String ID;
Connection con = OracleDBConnection.getConnection();
String query = "Insert into NEWSTUDENT values(?,?,?,?)";
PreparedStatement st = con.prepareStatement();
st.executeUpdate(query);
try {
BufferedReader bReader = new BufferedReader(new FileReader("1000rows.csv"));
while (bReader != null) {
String read;
try {
read = bReader.readLine();
if (read != null)
{
String[] array = read.split(",+");
for(String result:array)
{
System.out.println(result);
}
}
} catch (IOException ex) {
ex.printStackTrace();
}
finally
{
if (bReader == null)
{
bReader.close();
}
}
}
} catch (FileNotFoundException ex) {
ex.printStackTrace();
}
}
}
output:
1Kiriti
kiriti#gmail.com
880789939
Column names in Database:
Name Email Phone ID

Use Parepared statement and build a query in while Loop and execute it. For more on Prepared Statement please check Check this link
String sql = " INSERT INTO TABLE_(name,email,phone,id) VALUES(?,?,?,?) ";
try {
BufferedReader bReader = new BufferedReader(new FileReader("1000rows.csv"));
String line = "";
while ((line = bReader.readLine()) != null) {
try {
if (line != null)
{
String[] array = line.split(",+");
for(String result:array)
{
System.out.println(result);
//Create preparedStatement here and set them and excute them
PreparedStatement ps = yourConnecionObject.createPreparedStatement(sql);
ps.setString(1,str[0]);
ps.setString(2,str[1]);
ps.setString(3,str[2]);
ps.setString(4,strp[3])
ps.excuteUpdate();
ps. close()
//Assuming that your line from file after split will folllow that sequence
}
}
} catch (IOException ex) {
ex.printStackTrace();
}
finally
{
if (bReader == null)
{
bReader.close();
}
}
}
} catch (FileNotFoundException ex) {
ex.printStackTrace();
}

You can use Prepare Statement and set the value in parameter at each iteration:
Connection con = OracleDBConnection.getConnection();
String query = "Insert into NEWSTUDENT values(?,?,?,?)";
PreparedStatement ps=con.prepareStatement(query);
ps.setString(1,array[0]);
ps.setString(2,array[1]); // and so on
ps.executeUpdate();
If No of Rows are more you can also use Batch Processing :
String sql = "Insert into NEWSTUDENT values(?,?,?)";
PreparedStatement preparedStatement = null;
try{
preparedStatement =
connection.prepareStatement(sql);
preparedStatement.setString(1, "Gary");
preparedStatement.setString(2, "Larson");
preparedStatement.setString (3, "Test");
preparedStatement.addBatch();
preparedStatement.setString(1, "Stan");
preparedStatement.setString(2, "Lee");
preparedStatement.setString (3, 456);
preparedStatement.addBatch();
int[] affectedRecords = preparedStatement.executeBatch();
}finally {
if(preparedStatement != null) {
preparedStatement.close();
}
}

You can store your data in an array and bind them to your statement:
String query = "Insert into NEWSTUDENT values(?,?,?,?)";
PreparedStatement st = con.prepareStatement(query);
st.setString(1,array [0]);
st.setString(2,array[1]);
....
st.executeUpdate();
For more informations about prepared statements see the oracle documentation

Can we use two queries using prepared statement in one method

Can we use two queries in one method while using prepared statement, I have tried using this but invalid column name exception is coming.
My code snippets is as follows.
public double getPayroll(){
ResultSet rs = null;
ResultSet rs2 = null;
Connection conn = null;
PreparedStatement pstmt = null;
try {
conn = getDBConnection();
int employeeId;
String q1 = "select e_salary,e_house_rent,e_conv_allow,e_id
from employee";
pstmt = conn.prepareStatement(q1);
rs = pstmt.executeQuery();
double dailyPay=0,basicPay=0,payroll2=0;
int houseRent=0,convAllow=0;
while (rs.next()) {
dailyPay = rs.getInt(1)*.03;
houseRent=rs.getInt(2);
convAllow=rs.getInt(3);
employeeId=rs.getInt(4);
}
String q2="select att_status from attendance where
e_id=employeeId";
pstmt = conn.prepareStatement(q2);
rs2 = pstmt.executeQuery();
int noOfPresents = 0;
while(rs2.next()){
noOfPresents+=1;
}
basicPay=dailyPay*noOfPresents;
payroll2+=basicPay+houseRent+convAllow;
return payroll2;
} catch (Exception e) {
e.printStackTrace();
return 0.0;
} finally {
try {
rs.close();
pstmt.close();
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

Your problem is that the sql in q2 assumes that there is a column named employeeId, but I suspect you want to insert the value of the variable employeeId.
Change it to
select att_status from attendance where e_id=?
Then execute
pstmt.setString(1, employeeId);
before executing pstmt.executeQuery();

Retrieve column names from java.sql.ResultSet

With java.sql.ResultSet is there a way to get a column's name as a String by using the column's index? I had a look through the API doc but I can't find anything.

You can get this info from the ResultSet metadata. See ResultSetMetaData
e.g.
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
String name = rsmd.getColumnName(1);
and you can get the column name from there. If you do
select x as y from table
then rsmd.getColumnLabel() will get you the retrieved label name too.

In addition to the above answers, if you're working with a dynamic query and you want the column names but do not know how many columns there are, you can use the ResultSetMetaData object to get the number of columns first and then cycle through them.
Amending Brian's code:
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
// The column count starts from 1
for (int i = 1; i <= columnCount; i++ ) {
String name = rsmd.getColumnName(i);
// Do stuff with name
}

You can use the the ResultSetMetaData (http://java.sun.com/javase/6/docs/api/java/sql/ResultSetMetaData.html) object for that, like this:
ResultSet rs = stmt.executeQuery("SELECT * FROM table");
ResultSetMetaData rsmd = rs.getMetaData();
String firstColumnName = rsmd.getColumnName(1);

This question is old and so are the correct previous answers. But what I was looking for when I found this topic was something like this solution. Hopefully it helps someone.
// Loading required libraries
import java.util.*;
import java.sql.*;
public class MySQLExample {
public void run(String sql) {
// JDBC driver name and database URL
String JDBC_DRIVER = "com.mysql.jdbc.Driver";
String DB_URL = "jdbc:mysql://localhost/demo";
// Database credentials
String USER = "someuser"; // Fake of course.
String PASS = "somepass"; // This too!
Statement stmt = null;
ResultSet rs = null;
Connection conn = null;
Vector<String> columnNames = new Vector<String>();
try {
// Register JDBC driver
Class.forName(JDBC_DRIVER);
// Open a connection
conn = DriverManager.getConnection(DB_URL, USER, PASS);
// Execute SQL query
stmt = conn.createStatement();
rs = stmt.executeQuery(sql);
if (rs != null) {
ResultSetMetaData columns = rs.getMetaData();
int i = 0;
while (i < columns.getColumnCount()) {
i++;
System.out.print(columns.getColumnName(i) + "\t");
columnNames.add(columns.getColumnName(i));
}
System.out.print("\n");
while (rs.next()) {
for (i = 0; i < columnNames.size(); i++) {
System.out.print(rs.getString(columnNames.get(i))
+ "\t");
}
System.out.print("\n");
}
}
} catch (Exception e) {
System.out.println("Exception: " + e.toString());
}
finally {
try {
if (rs != null) {
rs.close();
}
if (stmt != null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
} catch (Exception mysqlEx) {
System.out.println(mysqlEx.toString());
}
}
}
}

SQLite 3
Using getMetaData();
DatabaseMetaData md = conn.getMetaData();
ResultSet rset = md.getColumns(null, null, "your_table_name", null);
System.out.println("your_table_name");
while (rset.next())
{
System.out.println("\t" + rset.getString(4));
}
EDIT: This works with PostgreSQL as well

import java.sql.*;
public class JdbcGetColumnNames {
public static void main(String args[]) {
Connection con = null;
Statement st = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/komal", "root", "root");
st = con.createStatement();
String sql = "select * from person";
rs = st.executeQuery(sql);
ResultSetMetaData metaData = rs.getMetaData();
int rowCount = metaData.getColumnCount();
System.out.println("Table Name : " + metaData.getTableName(2));
System.out.println("Field \tDataType");
for (int i = 0; i < rowCount; i++) {
System.out.print(metaData.getColumnName(i + 1) + " \t");
System.out.println(metaData.getColumnTypeName(i + 1));
}
} catch (Exception e) {
System.out.println(e);
}
}
}
Table Name : person
Field DataType
id VARCHAR
cname VARCHAR
dob DATE

while (rs.next()) {
for (int j = 1; j < columncount; j++) {
System.out.println( rsd.getColumnName(j) + "::" + rs.getString(j));
}
}

When you need the column names, but do not want to grab entries:
PreparedStatement stmt = connection.prepareStatement("SHOW COLUMNS FROM `yourTable`");
ResultSet set = stmt.executeQuery();
//store all of the columns names
List<String> names = new ArrayList<>();
while (set.next()) { names.add(set.getString("Field")); }
NOTE: Only works with MySQL

The SQL statements that read data from a database query return the data in a result set. The SELECT statement is the standard way to select rows from a database and view them in a result set. The **java.sql.ResultSet** interface represents the result set of a database query.
Get methods: used to view the data in the columns of the current row
being pointed to by the cursor.
Using MetaData of a result set to fetch the exact column count
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
boolean b = rsmd.isSearchable(1);
http://docs.oracle.com/javase/7/docs/api/java/sql/ResultSetMetaData.html
and further more to bind it to data model table
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try {
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to a selected database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
System.out.println("Connected database successfully...");
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql = "SELECT id, first, last, age FROM Registration";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
rs.close();
} catch(SQLException se) {
//Handle errors for JDBC
se.printStackTrace();
} catch(Exception e) {
//Handle errors for Class.forName
e.printStackTrace();
} finally {
//finally block used to close resources
try {
if(stmt!=null)
conn.close();
} catch(SQLException se) {
} // do nothing
try {
if(conn!=null)
conn.close();
} catch(SQLException se) {
se.printStackTrace();
} //end finally try
}//end try
System.out.println("Goodbye!");
}//end main
//end JDBCExample
very nice tutorial here : http://www.tutorialspoint.com/jdbc/
ResultSetMetaData meta = resultset.getMetaData(); // for a valid resultset object after executing query
Integer columncount = meta.getColumnCount();
int count = 1 ; // start counting from 1 always
String[] columnNames = null;
while(columncount <=count) {
columnNames [i] = meta.getColumnName(i);
}
System.out.println (columnNames.size() ); //see the list and bind it to TableModel object. the to your jtbale.setModel(your_table_model);

#Cyntech is right.
Incase your table is empty and you still need to get table column names you can get your column as type Vector,see the following:
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
Vector<Vector<String>>tableVector = new Vector<Vector<String>>();
boolean isTableEmpty = true;
int col = 0;
while(rs.next())
{
isTableEmpty = false; //set to false since rs.next has data: this means the table is not empty
if(col != columnCount)
{
for(int x = 1;x <= columnCount;x++){
Vector<String> tFields = new Vector<String>();
tFields.add(rsmd.getColumnName(x).toString());
tableVector.add(tFields);
}
col = columnCount;
}
}
//if table is empty then get column names only
if(isTableEmpty){
for(int x=1;x<=colCount;x++){
Vector<String> tFields = new Vector<String>();
tFields.add(rsmd.getColumnName(x).toString());
tableVector.add(tFields);
}
}
rs.close();
stmt.close();
return tableVector;

ResultSet rsTst = hiSession.connection().prepareStatement(queryStr).executeQuery();
ResultSetMetaData meta = rsTst.getMetaData();
int columnCount = meta.getColumnCount();
// The column count starts from 1
String nameValuePair = "";
while (rsTst.next()) {
for (int i = 1; i < columnCount + 1; i++ ) {
String name = meta.getColumnName(i);
// Do stuff with name
String value = rsTst.getString(i); //.getObject(1);
nameValuePair = nameValuePair + name + "=" +value + ",";
//nameValuePair = nameValuePair + ", ";
}
nameValuePair = nameValuePair+"||" + "\t";
}

If you want to use spring jdbctemplate and don't want to deal with connection staff, you can use following:
jdbcTemplate.query("select * from books", new RowCallbackHandler() {
public void processRow(ResultSet resultSet) throws SQLException {
ResultSetMetaData rsmd = resultSet.getMetaData();
for (int i = 1; i <= rsmd.getColumnCount(); i++ ) {
String name = rsmd.getColumnName(i);
// Do stuff with name
}
}
});

U can get column name and value from resultSet.getMetaData();
This code work for me:
Connection conn = null;
PreparedStatement preparedStatement = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = MySQLJDBCUtil.getConnection();
preparedStatement = conn.prepareStatement(sql);
if (params != null) {
for (int i = 0; i < params.size(); i++) {
preparedStatement.setObject(i + 1, params.get(i).getSqlValue());
}
ResultSet resultSet = preparedStatement.executeQuery();
ResultSetMetaData md = resultSet.getMetaData();
while (resultSet.next()) {
int counter = md.getColumnCount();
String colName[] = new String[counter];
Map<String, Object> field = new HashMap<>();
for (int loop = 1; loop <= counter; loop++) {
int index = loop - 1;
colName[index] = md.getColumnLabel(loop);
field.put(colName[index], resultSet.getObject(colName[index]));
}
rows.add(field);
}
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (preparedStatement != null) {
try {
preparedStatement.close();
}catch (Exception e1) {
e1.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return rows;

I know, this question is already answered but probably somebody like me needs to access a column name from DatabaseMetaData by label instead of index:
ResultSet resultSet = null;
DatabaseMetaData metaData = null;
try {
metaData = connection.getMetaData();
resultSet = metaData.getColumns(null, null, tableName, null);
while (resultSet.next()){
String name = resultSet.getString("COLUMN_NAME");
}
}