Archive for December, 2008

Exporting and Importing Admin-Objects from Matrix Database (0)

December 15th, 2008 by Frank Niedermann, under Matrix.

Export:

mql export Table BOMAnalysisReport xml into file file.xml;

Import: First show what would be imported and then import:

mql import Table * overwrite from file file.xml;
mql import list Table * overwrite from file file.xml;

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Get number of table rows from database (0)

December 10th, 2008 by Frank Niedermann, under Java.

Often it’s necessary to get the number of table rows from a database:

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String sql = "SELECT COUNT(*) AS rowcount FROM table";
int anzahl = 0;
Statement s = con.createStatement();
ResultSet r = s.executeQuery(sql);
r.next();
anzahl = r.getInt("rowcount");
r.close();
s.close();

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Using prepared Statements for similar queries (0)

December 10th, 2008 by Frank Niedermann, under Java.

It is useful to use prepared Statements instead of normal Statements if there are similar queries against the database.

Example:

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// Database connection
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection(dbUrl, dbUser, dbPassword);
 
// Normal Statement
Statement statement = con.createStatement();
ResultSet rs1 = statement.executeQuery("select * from customer");
while (rs1.next()) {
  String customerName = rs1.getString("customerName");
}
rs1.close();
statement.close();
 
// Prepared Statement
PreparedStatement preparedStatement = con.prepareStatement("select * from customer where customerName = ?);
preparedStatement.setString(1, "MyCustomer");
ResultSet rs2 = preparedStatement.executeQuery();
while (rs2.next()) {
  String customerName = rs2.getString("customerName");
}
rs2.close();
preparedStatement.close();
con.close();

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Advise Garbage Collector to clean the house (0)

December 10th, 2008 by Frank Niedermann, under Java.

It’s possible to tell the Garbage Collector that it’s now time to start and clean the house.

This is done by

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System.gc();

But this will only advise the Garbage Collector to run now, it won’t force the run.

May be useful after a big data import or something like that.

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Logging in Java with log4j (0)

December 10th, 2008 by Frank Niedermann, under Java.

Instead of System.out.println() and System.err.println() it is a good thing to use a logger, like log4j.

This is an example how it can be done:

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// creating a new Logger
private static final Logger logger = Logger.getLogger(MyLogger.class);
 
// configuration from XML-file
DOMConfigurator.configureAndWatch("logConfiguration.xml");
 
// log something
logger.info("Start");
 
// change log level
logger.setLevel(Level.ALL);
 
// log something more
logger.debug("Yep I was started");
logger.error("There is nothing to do!");

The configuration file:

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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <appender name="console" class="org.apache.log4j.ConsoleAppender"> 
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="%d %-5p [%c] %m%n"/> 
    </layout> 
  </appender> 
  <appender name="logfile" class="org.apache.log4j.FileAppender"> 
    <param name="file" value="MccImporter.log"/>
    <param name="Append" value="false"/>
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="%d %-5p [%c] %m%n"/> 
    </layout> 
  </appender> 
  <root> 
    <!-- ALL | DEBUG | INFO | WARN | ERROR | FATAL | OFF -->
    <priority value ="info" /> 
    <appender-ref ref="console" /> 
    <appender-ref ref="logfile" /> 
  </root>
</log4j:configuration>

I’m using two appenders, one for console output and one for a logfile. The logfile gets overwritten every time the Java application starts (Append=false).

If the log content is a very time consuming process to evaluate it could be better to first check if logging is enabled on the according level before evaluating the expressen:

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if (logger.isEnabledFor(Level.DEBUG)) {
  logger.debug(...);
}

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First Post! (1)

December 8th, 2008 by Frank Niedermann, under Stuff.

This is the first post!

public class Blog {
  public static void main(String[] args) {
    System.out.println("Hello Blog!");
  }
}