Re: please help: PostgreSQL JDBC Pooling problem - Mailing list pgsql-jdbc

Marcus,

OK, that reproduces.  The stack traces shows that it is this line of
code that is causing the null pointer exception:
               System.out.println("Statement = " + loStatement);

Specificly the toString() method on the loStatement object.  It isn't
the fact that loStatement is null, but a logic error in the toString()
method.  I don't yet know why the toString() method has a null pointer
exception, but in normal operations I wouldn't expect that code would be
calling toString on a Statement object.

thanks,
--Barry

Marcus Andree S. Magalhaes wrote:
> Barry,
>
> Try to change the openConnection method as follows:
>
> public Statement openConnection() {
>          Statement loStatement;
>          System.out.println("opening  con");
>          try {
>              // gets a connection from Pool
>              this.loConnection = loPoolSource.getConnection();
>              System.out.println("loConnection = " + this.loConnection);
>              loStatement = this.loConnection.createStatement();
>              System.out.println("Statement = " + loStatement);
>              return loStatement;
>              // return this.loConnection.createStatement();
>
>          } catch (Exception loException) {
>              loException.printStackTrace();
>          }
>
>          return null;
>      }
>
>
> With my system (Solaris x86, latest jdk 1.4 from Sun and postgresql 7.3.2) this
> results in a NullPointer Exception when printing loStatement on the screen.
>
> This seems to reproduce the error happening in my main application. The classes
> simply can't connect to the database because all Statements that openConnection()
> returns are null.
>
> BTW, is this the correct manner to implement a Pooled DB in PostgreSQL and
> a singleton class wrapped as a static attribute (loPoolSource) ??
>
>
> Thanks again.
>
> Marcus Andree
>
>
> Quoting Barry Lind <blind@xythos.com>:
>
>
>>Marcus,
>>
>>I can't reproduce your problem.  When I run the modifed version of your
>>test (changes made so that it compiles and runs standalone) I don't have
>>any errors.  My test table has about 1000 rows in it and everything
>>works fine without any errors.
>>
>>I am running the latest 7.3 build (109) against a 7.3.2 database using
>>the sun 1.4.1_01 jdk on Redhat8.
>>
>>Is there something else I need to do to reproduce the problem?
>>
>>thanks,
>>--Barry
>>
>>Marcus Andree S. Magalhaes wrote:
>>
>>>Dear list,
>>>
>>>
>>>I'm having a couple problems while implementing a JDBC Connection pool
>>
>>using
>>
>>>Postgresql Jdbc3PoolingDataSource.
>>>
>>>I was able to reproduce the errors with a simple java program. I'll be
>>>grateful if someone could analyse this problem for a while...
>>>
>>>The class io_property is a local class using standard java Properties
>>>classes to load data from a simple text file. This is done when calling
>>>the io_property.startService() static method.
>>>
>>>If I run the program exactly as show below, it works wonderfully. However,
>>>when commenting the return line of openConnection and uncommenting the
>>>previous 3 lines as:
>>>
>>>        this.loConnection = loPoolSource.getConnection();
>>>        System.out.println("loConnection = " + this.loConnection);
>>>        loStatement = this.loConnection.createStatement();
>>>        System.out.println("Statement = " + loStatement);
>>>        return loStatement;
>>>        // return this.loConnection.createStatement();
>>>
>>>The JDBC Statement returned is null. That's the problem I'm facing with my
>>>main application...
>>>
>>>Why is this happening?? In which circumstances
>>>does Connection.createStatement() return null???
>>>
>>>
>>>My main application is a bit different... It uses threads and lots of SQL
>>>code. I have to return a Statement instead of a Connection for historical
>>>reasons...
>>>
>>>
>>>Any help is welcome. The source file follows...
>>>
>>>
>>>Marcus
>>>
>>>
>>
>>===============================================================================
>>
>>>public class con_database {
>>>
>>>    static Jdbc3PoolingDataSource loPoolSource = null;
>>>    private Connection loConnection = null;
>>>
>>>    con_database() {
>>>    io_property.startService();
>>>    }
>>>
>>>    private static void setPool() {
>>>    // DataSource initialization
>>>    System.out.println("setPool()");
>>>    try {
>>>        System.out.println("setting pool");
>>>        // constructs a pool only when loPoolSource is not assigned.
>>>        // this will prevent problems if the same pool is set more than
>>>        // one time
>>>        if (loPoolSource == null) {
>>>        loPoolSource = new Jdbc3PoolingDataSource();
>>>        // DataSource configuration.
>>>
>>
>>        loPoolSource.setDataSourceName(io_property.DATABASE_POOL_DATA_SOURCE_NAME);
>>//
>>
>>>any name is valid here
>>>        loPoolSource.setServerName(io_property.DATABASE_POOL_SERVER_NAME);
>>>        loPoolSource.setPortNumber(io_property.DATABASE_POOL_SERVER_PORT);
>>>        loPoolSource.setDatabaseName(io_property.DATABASE_POOL_DATABASE_NAME);
>>>        loPoolSource.setUser(io_property.DATABASE_POOL_USER_NAME);
>>>        loPoolSource.setPassword(io_property.DATABASE_POOL_PASSWORD);
>>>        loPoolSource.setMaxConnections(io_property.DATABASE_POOL_MAXCONNECTIONS);
>>
>>>
>>>        } else {
>>>        System.out.println("pool is set");
>>>        return;
>>>        }
>>>    } catch (Exception loException) {
>>>        // logger.logToFile(loException);
>>>        loException.printStackTrace();
>>>    }
>>>
>>>    }
>>>
>>>
>>>
>>>    public Statement openConnection() {
>>>    Statement loStatement;
>>>    System.out.println("opening  con");
>>>    try {
>>>        // gets a connection from Pool
>>>        this.loConnection = loPoolSource.getConnection();
>>>        System.out.println("loConnection = " + this.loConnection);
>>>        // loStatement = this.loConnection.createStatement();
>>>        // System.out.println("Statement = " + loStatement);
>>>        // return loStatement;
>>>        return this.loConnection.createStatement();
>>>
>>>    } catch (Exception loException) {
>>>        loException.printStackTrace();
>>>    }
>>>
>>>    return null;
>>>    }
>>>
>>>    public void closeConnection() {
>>>    System.out.println("closing  con");
>>>    try {
>>>        if (this.loConnection != null) this.loConnection.close();
>>>    } catch (Exception loException) {
>>>        loException.printStackTrace();
>>>    }
>>>    }
>>>
>>>
>>>    public static void main(String args[]) {
>>>
>>>    Statement loStatement = null;
>>>    con_database loPoolConnection = new con_database();
>>>    loPoolConnection.setPool();
>>>    loStatement = loPoolConnection.openConnection();
>>>    ResultSet lors = null;
>>>    try {
>>>        lors = loStatement.executeQuery("select * from <tablename>");
>>>        while (lors.next()) {
>>>        System.out.println(lors.getString(1));
>>>        }
>>>    } catch (Exception e) {
>>>        e.printStackTrace();
>>>    }
>>>    finally {
>>>        try {
>>>        lors.close();
>>>        loStatement.close();
>>>        loPoolConnection.closeConnection();
>>>        } catch (Exception loException) {
>>>        loException.printStackTrace();
>>>        }
>>>    }
>>>
>>>    loPoolConnection = new con_database();
>>>    loPoolConnection.setPool();
>>>    loStatement = null;
>>>    loStatement = loPoolConnection.openConnection();
>>>    lors = null;
>>>    try {
>>>        lors = loStatement.executeQuery("select * from <table_name>");
>>>        while (lors.next()) {
>>>        System.out.println(lors.getString(2));
>>>        }
>>>    } catch (Exception e) {
>>>        e.printStackTrace();
>>>    }
>>>    finally {
>>>        try {
>>>        lors.close();
>>>        loStatement.close();
>>>        loPoolConnection.closeConnection();
>>>        } catch (Exception loException) {
>>>        loException.printStackTrace();
>>>        }
>>>    }
>>>     }
>>>   }
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>>
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>>>
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>>>
>>
>
>
>
>
> -------------------------------
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