使用静态类/方法中的方法级连接的池化数据库访问是否安全？

Question

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

Answer 1

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();
}