How do I parse an XML file using SAX?

By I Wayan Saryada in XML 0 Comment

This example show you how to read / parse an xml file using the SAX (Simple API for XML) parser. In the main class (SAXDemo) we create the instance of SAXParserFactory and the SAXParser. The SAXParser.parse() method will parse the given InputStream and handle the xml document using the SAXHandler class that we created.

package org.kodejava.xml;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.InputStream;

public class SAXDemo {
    public static void main(String[] args) throws Exception {
        // Creates a new instance of SAXParserFactory that in turn
        // creates a SAXParser.
        SAXParserFactory factory = SAXParserFactory.newInstance();
        SAXParser parser = factory.newSAXParser();

        // The handler that will listen to the SAX event during
        // the xml traversal.
        SAXHandler handler = new SAXHandler();
        InputStream data = SAXDemo.class.getResourceAsStream("/person.xml");
        parser.parse(data, handler);
    }
}

The SAXHandler class extended from the org.xml.sax.helpers.DefaultHandler class. The handler will listen to the event triggered by the SAXParser. This handler methods is defined by the interfaces such as the ContentHandler, ErrorHandler, DTDHandler, and EntityResolver.

For example to read the content of the XML file there are methods to listen to events such as startDocument, endDocument, startElement, endElement, etc, which defined by the ContentHandler interface.

package org.kodejava.xml;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class SAXHandler extends DefaultHandler {
    @Override
    public void startDocument() throws SAXException {
        System.out.println("startDocument");
    }

    @Override
    public void endDocument() throws SAXException {
        System.out.println("endDocument");
    }

    @Override
    public void startElement(String uri, String localName,
                             String qName, Attributes attributes)
            throws SAXException {
        System.out.println("startElement: " + qName);
    }

    @Override
    public void endElement(String uri, String localName,
                           String qName) throws SAXException {
        System.out.println("endElement");
    }

    @Override
    public void characters(char[] ch, int start, int length)
            throws SAXException {
        System.out.println("characters  : " + new String(ch, start, length));
    }
}

Here an example of the xml file will be read by our program:

<root>
    <persons>
        <person>
            <name>Foo</name>
        </person>
        <person>
            <name>Bar</name>
        </person>
    </persons>
</root>

Our program will print the following output:

startDocument
startElement: root
characters  : 

startElement: persons
characters  : 

startElement: person
characters  : 

startElement: name
characters  : Foo
endElement
characters  : 

endElement
characters  : 

startElement: person
characters  : 

startElement: name
characters  : Bar
endElement
characters  : 

endElement
characters  : 

endElement
characters  : 

endElement
endDocument

How do I check whether a thread group has been destroyed?

By I Wayan Saryada in Core API, Lang Package 0 Comment

You can use ThreadGroup.isDestroyed() method to check whether a thread group and its subgroups has been destroyed.

package org.kodejava.lang;

public class CheckGroupDestroy {
    public static void main(String[] args) {
        ThreadGroup grandParent = new ThreadGroup("GrandParent");
        ThreadGroup uncle = new ThreadGroup(grandParent, "Uncle");
        ThreadGroup parent = new ThreadGroup(grandParent, "Parent");
        ThreadGroup son = new ThreadGroup(parent, "Son");
        ThreadGroup daughter = new ThreadGroup(parent, "Daughter");
        ThreadGroup neighbour = new ThreadGroup("Neighbour");

        ThreadGroup[] groupArray = {
                grandParent, uncle, parent, son, daughter, neighbour
        };

        // Destroy 'parent' group and all its subgroups
        parent.destroy();

        // Check whether the group is destroyed. The result is,
        // GrandParent, Uncle, and Neighbour did not destroyed
        // because they are not Parent's subgroups
        for (ThreadGroup tg : groupArray) {
            if (tg.isDestroyed()) {
                System.out.println(tg.getName() + " is destroyed");
            } else {
                System.out.println(tg.getName() + " is not destroyed");
            }
        }
    }
}

The result is:

GrandParent is not destroyed
Uncle is not destroyed
Parent is destroyed
Son is destroyed
Daughter is destroyed
Neighbour is not destroyed

How do I destroy a thread group?

By I Wayan Saryada in Core API, Lang Package 0 Comment

You can destroy a thread group by using destroy() method of ThreadGroup class. It will cleans up the thread group and removes it from the thread group hierarchy. It’s not only destroy the thread group, but also all its subgroups.

The destroy() method is of limited use: it can only be called if there are no threads presently in the thread group.

package org.kodejava.lang;

public class ThreadGroupDestroy {
    public static void main(String[] args) {
        ThreadGroup root = new ThreadGroup("Root");
        ThreadGroup server = new ThreadGroup(root, "ServerGroup");
        ThreadGroup client = new ThreadGroup(root, "ClientGroup");

        // Destroy 'root' thread groups and all its subgroup
        // ('server' & 'client')
        root.destroy();

        // Check if 'root' group and its subgroups already destroyed
        if (root.isDestroyed()) {
            System.out.println("Root group is destroyed");
        }

        if (server.isDestroyed()) {
            System.out.println("Server group is destroyed");
        }

        if (client.isDestroyed()) {
            System.out.println("Client group is destroyed");
        }
    }
}

How to automatically close resources in JDBC?

By I Wayan Saryada in JDBC 0 Comment

One thing that we need to do manually when programming using JDBC is to make sure to close all the resources that we use. All resources including the ResultSet, Statement and Connection must be closed. This will usually produce a lot of boilerplate code in our program.

Starting from JDBC 4.1, which is a part of Java 7, we can use the try-with-resources statement to automatically manage the resources that we use. This try statement closes the resources used when the block finishes its execution either normally or abruptly.

Here is an example that shows us how to use the try-with-resources statement.

package org.kodejava.jdbc;

import java.sql.*;

public class TryWithResourceJdbc {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT * FROM product")) {

            while (rs.next()) {
                String code = rs.getString("code");
                String name = rs.getString("name");

                System.out.println("Code: " + code + "; Name: " + name);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I use try-with-resources statement?

By I Wayan Saryada in Basic, Core API 0 Comment

The try-with-resources statement is introduced in the Java 7. With this new statement we can simplify resource management in our program, also known as ARM (Automatic Resource Management).

This statement is a try statement that declares one or more resources. After the program finish with the resource, it must be closed. The try-with-resources ensures that each resource is closed and the end of the statement.

Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

package org.kodejava.basic;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class TryWithResourceExample {
    public static void main(String[] args) {
        try {
            TryWithResourceExample demo = new TryWithResourceExample();
            demo.printStream("F:/tmp/data.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void printStream(String fileName) throws IOException {
        char[] buffer = new char[1024];

        try (InputStream is = new FileInputStream(fileName);
             Reader reader = new BufferedReader(
                     new InputStreamReader(is, StandardCharsets.UTF_8))) {

            while (reader.read(buffer) != -1) {
                System.out.println(buffer);
            }
        }
    }
}