Java - Seite 7

Parse some HTML tags with a Java SAX XML parser

Parsing XML with Java is very simple. If you want to parse some HTML tags, then you just have to add a root element around those tags (to make it a valid XML structure) and then you can use the Java SAX XML parser.

Code

import java.io.StringReader;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
 
public class NewMain {
 
  public static void main(String[] args) throws Exception {
    String html = "<h1>Headline</h1><p><b>Hello World.</b><b>This is a test.</b></p>";
    html = "<root>" + html + "</root>";
 
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document document = builder.parse(new InputSource(new StringReader(html)));
    NodeList elementsByTagName = document.getElementsByTagName("b");
    for (int i = 0; i < elementsByTagName.getLength(); i++) {
      Node element = elementsByTagName.item(i);
      String text = element.getTextContent();
      System.out.println(text);
    }
  }
}

Result

Hello World.
This is a test.

Create GraphML XML file with Java

With Blueprints it is very easy to create a XML file following the GraphML standard. All you need is this:

import com.tinkerpop.blueprints.pgm.Vertex;
import com.tinkerpop.blueprints.pgm.impls.tg.TinkerGraph;
import com.tinkerpop.blueprints.pgm.util.io.graphml.GraphMLWriter;
import java.io.FileOutputStream;
import java.io.OutputStream;
 
public class App {
 
  private static final String OUTPUT_FILE = "./res/graph.graphml";
 
  public static void main(String[] args) throws Exception {
    OutputStream out = new FileOutputStream(OUTPUT_FILE);
    TinkerGraph graph = new TinkerGraph();
 
    Vertex source = graph.addVertex("1");
    Vertex target = graph.addVertex("2");
    graph.addEdge("3", source, target, "connection");
 
    GraphMLWriter writer = new GraphMLWriter(graph);
    writer.outputGraph(out);
  }
}

This is what you will get then:

graph.graphml

<?xml version="1.0" ?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns">
  <graph id="G" edgedefault="directed">
    <node id="2"></node>
    <node id="1"></node>
    <edge id="3" source="1" target="2" label="connection"></edge>
  </graph>
</graphml>

Write string to file with Java 7

With Java 7 it is very easy to read and write files. If you want to put a string into a file, then you can do the following:

Version 1

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
 
public class JavaApplication{
  public static void main(String[] args) throws IOException {
    String text = "Hello World.";
    Path target = Paths.get("C:/dev/temp/test.txt");
 
    InputStream is = new ByteArrayInputStream(text.getBytes());
    Files.copy(is, target, StandardCopyOption.REPLACE_EXISTING);
  }
}

You can also do this:

Version 2

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
 
public class JavaApplication6 {
 
  public static void main(String[] args) throws IOException {
    String text = "Hello World.";
    Path target = Paths.get("C:/dev/temp/test.txt");
 
    Path file = Files.createFile(target);
    Files.write(file, text.getBytes(), StandardOpenOption.WRITE);
  }
}

In older Java versions you can do it like this (but you should use some try-catch-blocks to close the streams):

Version 3

import java.io.*;
 
public class JavaApplication{
 
  public static void main(String[] args) throws IOException {
    String text = "Hello World.";
    File target = new File("C:/dev/temp/test.txt");
 
    FileOutputStream fos = new FileOutputStream(target, false);
    BufferedWriter br = new BufferedWriter(new OutputStreamWriter(fos));
    br.write(text);
    br.flush();
    br.close();
    fos.flush();
    fos.close();
  }
}

With Java 7 you don’t need try-catch-blocks because you can use try-with-resources:

Version 4

import java.io.*;
 
public class JavaApplication{
 
  public static void main(String[] args) throws IOException {
    String text = "Hello World.";
    File target = new File("C:/dev/temp/test.txt");
 
    try (FileOutputStream fos = new FileOutputStream(target, false)) {
      try (BufferedWriter br = new BufferedWriter(new OutputStreamWriter(fos))) {
        br.write(text);
        br.flush();
      }
      fos.flush();
    }
  }
}

Version 5

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
 
public class JavaApplication {
 
  public static void main(String[] args) {
    String text = "Hello World.";
    File target = new File("C:/dev/temp/test.txt");
 
    FileWriter writer = null;
    try {
      writer = new FileWriter(target, false);
      writer.write(text);
    } catch (IOException ex) {
      Logger.getLogger(JavaApplication.class.getName()).log(Level.SEVERE, null, ex);
    } finally {
      if (writer != null) {
        try {
          writer.close();
        } catch (IOException ex) {
          Logger.getLogger(JavaApplication.class.getName()).log(Level.SEVERE, null, ex);
        }
      }
    }
  }
}

Export a GraphML graph as image with Java

In my post „How to parse GraphML files with a cool Java library“ I showed how to parse a GraphML XML file. In this post I want to show you, how you can visualize it. All you need is the yEd – Graph Editor and some extra markup in your XML file.
Export a GraphML graph as image with Java weiterlesen

How to parse GraphML files with a cool Java library

I’ve found this great GraphML reader and writer library: Blueprints. There is also a good documentation on how to use the GraphML library for reading XML-encoded graphs. Anyway, I think my example is better. 🙂
How to parse GraphML files with a cool Java library weiterlesen

Where does Maven store the dependencies?

Last time I declared this Maven dependency in my pom.xml:

<dependency>
  <groupId>com.tinkerpop.blueprints</groupId>
  <artifactId>blueprints-core</artifactId>
  <version>1.2</version>
</dependency>

I then requested the download of this dependency and got blueprints-core-1.2.jar. But where has this dependency been saved? I then found out that the dependencies are saved to the user’s Maven home directory (e.g. C:\Users\bennyn\.m2).

Finally I found the file here:
C:\Users\bennyn\.m2\repository\com\tinkerpop\blueprints\blueprints-core\1.2\blueprints-core-1.2.jar

You can also specify the location yourself. To do that, you just have to change the Maven local repository in the settings.xml:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>C:\dev\temp</localRepository>
  ...
</settings>