I have this class (my database connection factory):
#ApplicationScoped
public class ConnectionFactory {
private ComboPooledDataSource datasource;
private Long open = 0l;
private Long close = 0l;
#PostConstruct
public void init() throws PropertyVetoException, SQLException {
datasource = new ComboPooledDataSource();
datasource.setDriverClass("org.postgresql.Driver");
datasource.setJdbcUrl("jdbc:postgresql:dbcampanha");
datasource.setUser("postgres");
datasource.setPassword("admin");
datasource.setMinPoolSize(1);
datasource.setMaxPoolSize(5);
datasource.setCheckoutTimeout(30000);
datasource.setUnreturnedConnectionTimeout(30);
datasource.setMaxIdleTime(30);
datasource.setDebugUnreturnedConnectionStackTraces(true);
datasource.setAcquireIncrement(1);
}
#Produces
#RequestScoped
public Connection getConnection() throws ClassNotFoundException {
open++;
try {
Connection connection = datasource.getConnection();
connection.setAutoCommit(false);
return connection;
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
public void close(#Disposes Connection connection) {
close++;
try {
connection.commit();
connection.close();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
public Long getOpenedConnectionCounter() {
return open;
}
public Long getClosedConnectionCounter(){
return close;
}
public ComboPooledDataSource getDatasource(){
return datasource;
}
}
I use this class with an JAX-RS application. And for some tests using this route:
#RequestScoped
#Path("/test")
public class TesteService {
#Inject
private Connection connection;
#GET
#Produces(MyMediaType.JSON)
#Path("/yes")
public Response success() throws SQLException {
connection.getClientInfo("");
return Response.ok().build();
}
}
And this class for my Client:
public class TesteMain {
private static final String prefix = "http://localhost:8080/schoolwork/service/test/";
public static void main(String[] args) throws InterruptedException {
for (int i = 0; i < 10000; i++) {
Request request = new Request(prefix + "yes");
request.start();
if(i % 10 == 0)
Thread.sleep(1000l);
}
}
public static class Request extends Thread {
private String rota;
public Request(String rota){
this.rota = rota;
}
#Override
public void run() {
try {
HttpURLConnection url = (HttpURLConnection) (new URL(rota).openConnection());
url.connect();
System.out.println(url.getResponseCode() == 200 ? "SUCCESS" : "ERROR");
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
I receive this infos:
{
"opened-connection": 789,
"closed-connection": 867,
}
Yes, I have a number of closed database connection greater than opened. HOW? Any idea for this?
I use
Tomcat 7 + Java 7
P.S. I am sorry for my bad English :/
SOLVED
I change my counters for AtomicInteger objects, and works perfectly.
So, two quick comments:
Your counters are (boxed) longs read and updated willy-nilly by 1000 concurrent Threads. Their values will in general be unpredictable and nondeterministic. They certainly won't accurately count what you intend them to count. Consider using atomic operations on AtomicLongs instead.
Your commit() (or rollback()) should be attached to your database business logic, the part where you can tell a unit of work has either succeeded or failed. You shouldn't automatically commit on close.
have been a long-time reader here and now I`ve got a problem I can´t really get my head around.
For ease of access and to save object creation overhead I have a static class realizing database accesses. The used JVM implementation is Tomcat and for connection pooling org.apache.commons.dbcp is used.
I've read a lot about thread-safety, heap and stack here and elsewhere but I can`t get to a definitive conclusion if multiple method calls on my static class won't interfere with each other. Most topics I've read deal with instance methods while I use static ones which might have implications I overlooked.
If I understood everything correctly, as the variables connection, statement, resultset are on the method level, each function call should have a unique reference on the stack to a unique object in the heap and it should not be possible that multiple method calls interfere with each other.
Am I right or do I stand corrected? Any help would be appreciated.
The (shortened) code is :
public class DBQuery{
private static String pathToDataSource = "";
private static javax.naming.Context cxt = null;
private static javax.sql.DataSource ds = null;
private static void getDataSource() throws Exception {
if(pathToDataSource.equals("")){ pathToDataSource = Config.getParam("PathToDataSource"); }
cxt = new javax.naming.InitialContext();
ds = (javax.sql.DataSource) cxt.lookup(pathToDataSource);
}
private static Connection connect() throws Exception {
if(ds==null){ getDataSource(); }
return ds.getConnection();
}
public static Vector doDBquery(String querystring) throws Exception {
Vector retVec = new Vector();
Connection connection = null;
Statement statement = null;
ResultSet resultset = null;
try {
connection = getConnection();
statement = connection.createStatement();
resultset = statement.executeQuery(querystring);
...
} catch(Exception e) {
...
} finally {
myFinallyBlock(resultset, statement, connection);
}
return retVec;
}
// more methods like doDBInsert() following, hence closure in separate myFinallyBlock
private static void myFinallyBlock(ResultSet resultset, Statement statement, Connection connection) {
try {
if (resultset != null) resultset.close();
} catch (SQLException e) { resultset = null; }
try {
if (statement != null) statement.close();
} catch (SQLException e) { statement = null; }
try {
if (connection != null) connection.close();
} catch (SQLException e) { connection = null; }
}
} //close class
Yeah, you are right inside method there is no concurrency problems , until you are using shared variables inside it, in other words "Stateless objects are always thread-safe."
Servlet is quite good example of it ;)
edited.
For making your code safe I recommend you to do follow:
private static Connection connect() throws Exception {
if (ds == null) {
synchronized (Connection.class) {
if (ds == null) {
getDataSource();
}
}
}
return ds.getConnection();
}
This class is the only thing that should ever access the database and I'd like to give it a single connection object when my application starts up. However, instantiation may cause an exception to be thrown, so I can't do this:
public class DBManager {
private static Connection conn = Database.getReadOnlyConnection();
...
...
}
I have a pretty ugly workaround, and I was wondering if there's a better way.
public class DBManager {
private static Connection conn = null;
private static DBManager instance = null;
public static DBManager getInstance() throws SQLException, ClassNotFoundException {
if (instance == null){
instance = new DBManager();
}
return instance;
}
private DBManager() throws SQLException, ClassNotFoundException {
conn = Database.getReadOnlyConnection();
}
...
...
}
There's also this alternative:
public class DBManager {
private static Connection conn = null;
public static void setConnection(Connection conn) throws NotSupportedException{
if (conn == null){
this.conn = conn;
}
else {
throw new NotSupportedException();
}
}
...
...
}
Is there a nicer way of handling this in Java?
Update
I've decided to use a static initializer block.
public class DBManager {
private static Connection conn;
static {
try {
conn = getReadOnlyConnection();
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
...
...
}
This causes the application to fail early if the database cannot be reached and avoids the problem of having to ensure that the DBManager is only being used via an instance.
You program should be more robust - sure you may have a connection now, but what happens if the DB does down - use the same logic for no DB now as DB goes down later
How about a static method and checking if the connection is still valid,
public class Config{
private static Connection con;
private String dbUrl = "jdbc:mysql:/localhost:3306/dbname","username","password";
public static Connection getConnection() throws SQLException{
if(con== null){
con = DriverManager.getConnection(dbUrl);
}
if(!con.isValid(10)){
con = DriverManager.getConnection.getConnection(dbUrl);
}
return con;
}
}
Need code to create the connection pool in java?
How does we make sure that connection pool doesn't return the same object which is already in use?
How happens if client closed the connection after taking it out from Connection pool?
Update 1:
I want to create this in Simple Java terms and want to see how it works in Multithreading Env. I mean which methods would be synchronized and which are not. Also will this class would be a public class? If yes then any one can access this class and reinitialize the connection pool?
Update 2:
I have some code as below. But i don't how "Closing a connection coming from a pool returns it to the pool, it doesn't close the connection physically."
Also i didn't understood this "Because if a connection has been borrowed from the pool and not returned yet, it's not "available" and can't be redistributed to another client of the pool."
import java.util.*;
import java.sql.*;
class ConnectionPoolManager
{
String databaseUrl = "jdbc:mysql://localhost:3306/myDatabase";
String userName = "userName";
String password = "userPass";
Vector connectionPool = new Vector();
public ConnectionPoolManager()
{
initialize();
}
public ConnectionPoolManager(
//String databaseName,
String databaseUrl,
String userName,
String password
)
{
this.databaseUrl = databaseUrl;
this.userName = userName;
this.password = password;
initialize();
}
private void initialize()
{
//Here we can initialize all the information that we need
initializeConnectionPool();
}
private void initializeConnectionPool()
{
while(!checkIfConnectionPoolIsFull())
{
System.out.println("Connection Pool is NOT full. Proceeding with adding new connections");
//Adding new connection instance until the pool is full
connectionPool.addElement(createNewConnectionForPool());
}
System.out.println("Connection Pool is full.");
}
private synchronized boolean checkIfConnectionPoolIsFull()
{
final int MAX_POOL_SIZE = 5;
//Check if the pool size
if(connectionPool.size() < 5)
{
return false;
}
return true;
}
//Creating a connection
private Connection createNewConnectionForPool()
{
Connection connection = null;
try
{
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(databaseUrl, userName, password);
System.out.println("Connection: "+connection);
}
catch(SQLException sqle)
{
System.err.println("SQLException: "+sqle);
return null;
}
catch(ClassNotFoundException cnfe)
{
System.err.println("ClassNotFoundException: "+cnfe);
return null;
}
return connection;
}
public synchronized Connection getConnectionFromPool()
{
Connection connection = null;
//Check if there is a connection available. There are times when all the connections in the pool may be used up
if(connectionPool.size() > 0)
{
connection = (Connection) connectionPool.firstElement();
connectionPool.removeElementAt(0);
}
//Giving away the connection from the connection pool
return connection;
}
public synchronized void returnConnectionToPool(Connection connection)
{
//Adding the connection from the client back to the connection pool
connectionPool.addElement(connection);
}
public static void main(String args[])
{
ConnectionPoolManager ConnectionPoolManager = new ConnectionPoolManager();
}
}
Need code to create the connection pool in java?
Not sure what the question is but don't create yet another connection pool, use an existing solution like C3P0, Apache DBCP, Proxool or BoneCP (a new player in that field). I would use C3P0.
How does we make sure that connection pool doesn't return the same object which is already in use?
Because if a connection has been borrowed from the pool and not returned yet, it's just not in the pool and can't be assigned to another client of the pool (resources are removed from the pool until they are returned).
How happens if client closed the connection after taking it out from Connection pool?
The connection a client gets from a pool is not really a java.sql.Connection, it's a wrapper (a proxy) for a java.sql.Connection that customizes the behavior of some methods. The close() method is one of them and does not close the Connection instance but returns it to the pool.
Don't write your own. There are plenty of librarires out there that will do this for you that are open source and easy to use and will have solved all the problems you'll encounter trying to make it yourself.
Here is a simple example that uses Apache's Commons DBCP and Commons Pool:
First set up a DataSource.
javax.sql.DataSource source = new org.apache.commons.dbcp.BasicDataSource();
source.setDriverClassName("com.mysql.jdbc.Driver");
source.setUsername("username");
source.setPassword("password");
source.setUrl("jdbc:mysql://localhost:3306/myDatabase");
Once you have a DataSource, it is easy to get a connection from the pool.
java.sql.Connection connection = source.getConnection();
closing the connection will return it to the pool for you.
connection.close();
I hope this source code helps
http://jagadeeshmanne.blogspot.com/2014/03/connection-pool-in-java-jdbc.html
Configuration.java
package com.jmanne.utils;
public class Configuration {
public String DB_USER_NAME ;
public String DB_PASSWORD ;
public String DB_URL;
public String DB_DRIVER;
public Integer DB_MAX_CONNECTIONS;
public Configuration(){
init();
}
private static Configuration configuration = new Configuration();
public static Configuration getInstance(){
return configuration;
}
private void init(){
DB_USER_NAME = "root"
DB_PASSWORD = "root"
DB_URL = "jdbc:mysql://localhost:3306/jmanne"
DB_DRIVER = "com.mysql.jdbc.Driver"
DB_MAX_CONNECTIONS = 5
}
}
JdbcConnectionPool.java
package com.jmanne.db;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.jmanne.utils.Configuration;
import com.mysql.jdbc.Connection;
public class JdbcConnectionPool {
List<connection> availableConnections = new ArrayList<connection>();
public JdbcConnectionPool()
{
initializeConnectionPool();
}
private void initializeConnectionPool()
{
while(!checkIfConnectionPoolIsFull())
{
availableConnections.add(createNewConnectionForPool());
}
}
private synchronized boolean checkIfConnectionPoolIsFull()
{
final int MAX_POOL_SIZE = Configuration.getInstance().DB_MAX_CONNECTIONS;
if(availableConnections.size() < MAX_POOL_SIZE)
{
return false;
}
return true;
}
//Creating a connection
private Connection createNewConnectionForPool()
{
Configuration config = Configuration.getInstance();
try {
Class.forName(config.DB_DRIVER);
Connection connection = (Connection) DriverManager.getConnection(
config.DB_URL, config.DB_USER_NAME, config.DB_PASSWORD);
return connection;
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
public synchronized Connection getConnectionFromPool()
{
Connection connection = null;
if(availableConnections.size() > 0)
{
connection = (Connection) availableConnections.get(0);
availableConnections.remove(0);
}
return connection;
}
public synchronized void returnConnectionToPool(Connection connection)
{
availableConnections.add(connection);
}
}
DataSource.java
package com.jmanne.db;
import java.sql.SQLException;
import com.mysql.jdbc.Connection;
public class DataSource {
static JdbcConnectionPool pool = new JdbcConnectionPool();
public static Connection getConnection() throws ClassNotFoundException, SQLException{
Connection connection = pool.getConnectionFromPool();
return connection;
}
public static void returnConnection(Connection connection) {
pool.returnConnectionToPool(connection);
}
}
Just use Semaphores. Ideally what you should do is use CP3O or DBCP as your connection pool. Now you can throttle you connection based on Semaphore.
Every time you do Get, you acquire and on every Release you release it from Semaphore. More over semaphores are thread safe.
Use one of the existing, e.g. Apache DBCP
The connections returned by the pool are often proxies which "ignore" the call to close() from the application. When the connections are returned to the pool, they can be reused. Pools also close and reopen automatically if necessary.
If your application runs on a server, then configure as Data Source, where server will take care of Pooling or else if a simple Java Client then use Apache DBCP(if to the database) or else use Apache Commons Pooling API
See here: Apache Commons
One argument for rolling your own connpool is the configuration and additional jars that are avoided. I agree you need to enable the 3rd party interfaces so you can swap in a mature connpool, but having your own tiny solution can have its place. Self cleaning Vector with synchronized block and a conn wrapper with close() marking the conn as available works very well for servlet apps.
I have one solution for the same to create a connection pool utility which can help you create a pool of default size 10.
#Component
public class ConnectionPool {
private static final Logger logger = LoggerFactory.getLogger(ConnectionPool.class);
private static final int MAX_POOL_SIZE_LIMIT = 10;
private BlockingQueue activeConnectinoQueue = new LinkedBlockingQueue<>();
private BlockingQueue usedConnectinoList = new LinkedBlockingQueue<>();
private int initialPoolSize = 5;
#Autowired
#Qualifier("dataSource")
private DataSource dataSource;
public void initConnectionPool() {
logger.info("ConnectionPool initialization started.");
if(activeConnectinoQueue.isEmpty() && usedConnectinoList.isEmpty()) {
for (int i=0; i<initialPoolSize; i++) {
createConnections();
}
}
logger.info("ConnectionPool initialization completed. ConnectionPool size : {}", activeConnectinoQueue.size());
}
private void createConnections() {
try {
Connection connection = dataSource.getConnection();
activeConnectinoQueue.add(connection);
}catch (SQLException e) {
logger.error("Error in getting connection from pool : ", e);
}
}
public Connection getConnection() {
if(activeConnectinoQueue.isEmpty()) {
initConnectionPool();
}
Connection connection = activeConnectinoQueue.remove();
try {
if(connection.isClosed()) {
connection = dataSource.getConnection();
}
}catch (SQLException e) {
logger.error("Error while getting connection from pool : ", e);
}
usedConnectinoList.add(connection);
return connection;
}
public void releaseConnection(Connection connection) {
if(connection != null) {
usedConnectinoList.remove(connection);
activeConnectinoQueue.add(connection);
}
}
public void setInitialPoolSize(int initialPoolSize) {
if(!(initialPoolSize < 0 || initialPoolSize > MAX_POOL_SIZE_LIMIT)) {
this.initialPoolSize = initialPoolSize;
}
}
public int getInitialPoolSize() {
return initialPoolSize;
}
public int getConnectionPoolSize() {
return activeConnectinoQueue.size() + usedConnectinoList.size();
}
public void setDataSource(AbstractDataSource dataSource) {
this.dataSource = dataSource;
}
public void closeConnectionPool() {
logger.info("Closing connectionPool started.");
close(usedConnectinoList);
close(activeConnectinoQueue);
logger.info("ConnectionPool Closed.");
}
private void close(BlockingQueue<Connection> connectinosQueue) {
for (int i=0; i<connectinosQueue.size(); i++) {
Connection connection = connectinosQueue.remove();
if(connection != null) {
try {
connection.close();
} catch (SQLException e) {
logger.error("Error in initializing connection pool : ", e);
}
}
}
}
}
now To make it safe we need to attach a factory object..
public enum ConnectionFactory {
CONNECTION;
private ConnectionPool connectionPool;
public void setConnectionPool(ConnectionPool connectionPool) {
this.connectionPool = connectionPool;
}
public Connection getConnection() {
return connectionPool.getConnection();
}
public void closeConnection() {
connectionPool.closeConnectionPool();
}
public void releaseConnection(Connection connection) {
connectionPool.releaseConnection(connection);
}
public int getConnectionPoolSize() {
return connectionPool.getConnectionPoolSize();
}
#Component
public static class ConnectionBuilder {
#Autowired
private ConnectionPool connectionPool;
public void setConnectionPool(ConnectionPool connectionPool) {
this.connectionPool = connectionPool;
}
#PostConstruct
public void postConstruct() {
for (ConnectionFactory cfactory : EnumSet.allOf(ConnectionFactory.class)) {
cfactory.setConnectionPool(connectionPool);
}
}
}
}
Java Connection Pool ?
There are three way to create JDBC Connection Pooling is very easy...
Apache Commons DBCP
public class DBCPDataSource {
private static BasicDataSource ds = new BasicDataSource();
static {
ds.setUrl("jdbc:h2:mem:test");
ds.setUsername("user");
ds.setPassword("password");
ds.setMinIdle(5);
ds.setMaxIdle(10);
ds.setMaxOpenPreparedStatements(100);
}
public static Connection getConnection() throws SQLException {
return ds.getConnection();
}
private DBCPDataSource(){ }
}
Now you can get connection
Connection con = DBCPDataSource.getConnection();
HikariCP
public class HikariCPDataSource {
private static HikariConfig config = new HikariConfig();
private static HikariDataSource ds;
static {
config.setJdbcUrl("jdbc:h2:mem:test");
config.setUsername("user");
config.setPassword("password");
config.addDataSourceProperty("cachePrepStmts", "true");
config.addDataSourceProperty("prepStmtCacheSize", "250");
config.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
ds = new HikariDataSource(config);
}
public static Connection getConnection() throws SQLException {
return ds.getConnection();
}
private HikariCPDataSource(){}
}
Now you can get connection
Connection con = HikariCPDataSource.getConnection();
C3PO
public class C3poDataSource {
private static ComboPooledDataSource cpds = new ComboPooledDataSource();
static {
try {
cpds.setDriverClass("org.h2.Driver");
cpds.setJdbcUrl("jdbc:h2:mem:test");
cpds.setUser("user");
cpds.setPassword("password");
} catch (PropertyVetoException e) {
// handle the exception
}
}
public static Connection getConnection() throws SQLException {
return cpds.getConnection();
}
private C3poDataSource(){}
}
Now you can get connection
Connection con = C3poDataSource.getConnection();
I have some model code in Java which has connection pool with multithreading.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Iterator;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
abstract class ObjectPool<T> {
private ConcurrentLinkedQueue<T> pool;
ScheduledExecutorService executorService;
ObjectPool(int minObjects) {
pool = new ConcurrentLinkedQueue<T>();
for (int i = 0; i < minObjects; i++) {
pool.add(createObject());
}
}
ObjectPool(final int minObjects, final int maxSize, final long interval){
pool = new ConcurrentLinkedQueue<T>();
for (int i = 0; i < minObjects; i++) {
pool.add(createObject());
}
executorService = Executors.newSingleThreadScheduledExecutor();
executorService.scheduleWithFixedDelay(new Runnable(){
public void run() {
int size = pool.size();
while(size > maxSize){
pool.remove();
}
Iterator i = pool.iterator();
while(i.hasNext()){
T t = (T) i.next();
if(checkExpiry(t)){
System.out.println("Expiry existed...");
i.remove();
}
}
while(pool.size() < minObjects){
System.out.println("Adding more objects to pool");
pool.add(createObject());
}
}
}, interval, interval, TimeUnit.MILLISECONDS);
}
public T borrowObject() {
if (pool.peek() == null)
return createObject();
return pool.remove();
}
public void addObject(T obj) {
if (obj == null)
return;
pool.add(obj);
}
public abstract T createObject();
public abstract boolean checkExpiry(T t);
}
class MultithreadQuery extends Thread{
private ObjectPool<Connection> pool;
private int threadNo;
String query;
MultithreadQuery(ObjectPool<Connection> pool,int threadNo, String query){
this.pool = pool;
this.threadNo = threadNo;
this.query = query;
}
#Override
public void run(){
Connection con = pool.borrowObject();
Statement stmt;
try {
stmt = con.createStatement();
System.out.println("Query started for thread->"+ threadNo);
ResultSet rs=stmt.executeQuery(query);
while(rs.next())
System.out.println(rs.getInt(1)+" "+rs.getString(2)+" "+rs.getString(3));
System.out.println("closing connection....");
con.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
pool.addObject(con);
System.out.println("Query ended for thread->"+ threadNo);
}
}
public class ObjectPoolPatternDemo {
ObjectPool<Connection> pool;
public void setUp(){
pool = new ObjectPool<Connection>(4, 10, 1) {
#Override
public Connection createObject() {
Connection con;
try {
con = DriverManager.getConnection("URL","Username","Password");
return con;
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
#Override
public boolean checkExpiry(Connection conn) {
boolean expiryFlag = false;
try {
if(conn.isClosed())
expiryFlag = true;
} catch (SQLException e) {
e.printStackTrace();
}
return expiryFlag;
}
};
}
public static void main(String[] args) throws SQLException {
ObjectPoolPatternDemo oppd = new ObjectPoolPatternDemo();
oppd.setUp();
ExecutorService es = Executors.newFixedThreadPool(4);
String query = "select * from TABLE";
es.execute(new MultithreadQuery(oppd.pool,1,query));
es.execute(new MultithreadQuery(oppd.pool,2,query));
es.execute(new MultithreadQuery(oppd.pool,3,query));
es.execute(new MultithreadQuery(oppd.pool,4,query));
es.execute(new MultithreadQuery(oppd.pool,5,query));
es.execute(new MultithreadQuery(oppd.pool,6,query));
es.shutdown();
try {
es.awaitTermination(1, TimeUnit.DAYS);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("finally completed...");
}
}
I need a database connection in Java Web service implemented as a session bean, and I'm not sure if I do it right.
I created a class
public final class SQLUtils {
//.....
private static DataSource m_ds=null;
static
{
try
{
InitialContext ic = new InitialContext();
m_ds = (DataSource) ic.lookup(dbName); //Connection pool and jdbc resource previously created in Glassfish , dbName contains the proper JNDI resource name
}
catch (Exception e)
{
e.printStackTrace();
m_ds = null;
}
}
public static Connection getSQLConnection() throws SQLException
{
return m_ds.getConnection();
}
}
Whenever I need a connection I do
Connection cn = null;
try
{
cn = SQLUtils.getSQLConnection();
// use connection
}
finally
{
if (null != cn)
{
try
{
cn.close();
}
catch (SQLException e)
{
}
}
}
Is it ok to use it this way, or I DataSource must be a member of the bean ?
#Stateless
#WebService
public class TestBean {
private #Resource(name=dbName) DataSource m_ds;
}
I'm sorry if it is a nube question, but I'm pretty new to Java. Thanks in advance.
Apart from the C-style formatting, a few unnecessary lines and a bit poor exception handling, you can just do so.
Here's how I'd do it:
public final class SQLUtil {
private static DataSource dataSource;
// ..
static {
try {
dataSource = (DataSource) new InitialContext().lookup(name);
} catch (NamingException e) {
throw new ExceptionInInitializerError(e);
}
}
public static Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
}
I throw here ExceptionInInitializerError so that the application will immediately stop so that you don't need to face "unexplainable" NullPointerException when trying to obtain a connection.
In the ancient J2EE world, the traditional way to manage this was to use a ServiceLocator. Below, a sample implementation (non optimized, the DataSource could be cached):
public class ServiceLocator {
private Context initalContext;
private static ServiceLocator ourInstance = new ServiceLocator();
public static ServiceLocator getInstance() {
return ourInstance;
}
private ServiceLocator() {
try {
this.initalContext = new InitialContext();
} catch (NamingException ex) {
throw new ServiceLocatorException(...);
}
}
public DataSource getDataSource(String dataSourceName) {
DataSource datasource = null;
try {
Context ctx = (Context) initalContext.lookup("java:comp/env");
datasource = (DataSource) ctx.lookup(dataSourceName);
} catch (NamingException ex) {
throw new ServiceLocatorException(...);
}
return datasource;
}
}
To use it, simply call it like this:
DataSource ds = ServiceLocator.getInstance().getDataSource("jdbc/mydatabase");
But this was prior to the EJB3 and Dependency Injection era. Now, when using EJB3, if you have setup your DataSource in your EJB container, all you have to do to automatically inject the DataSource in your Stateless Bean is to write (where mydatabase is the name of the datasource):
#Resource
private DataSource mydatabase;
Use the name attribute if you want to explicitly, well, set the name:
#Resource(name="jdbc/mydatabase")
private DataSource dataSource;
EJB3 actually make the ServiceLocator pattern obsolete and you should really prefer injection when working with them.
Um, isn't this an example to a JDBC DataSource, not a Glassfish Connection Pool?