The first wurblet

Quickstart

Create a subdirectory with the name wurblets and in this directory create another pom.xml with the following contents:



  4.0.0

  
    com.example
    wurbelizer-tutorial
    1.0-SNAPSHOT
  

  org.example
  wurblets
  1.0-SNAPSHOT

  
    
      org.wurbelizer
      wurbelizer
      ${wurbelizer.version}
    
  

  
    
      
        org.wurbelizer
        wurbelizer-maven-plugin
        
          
            
              wurbile

The execution goal wurbile translates the wurblet source code to compilable Java and a resource file holding strings.

The wurbelizer can load and execute any Java class that implements the interface org.wurbelizer.wurblet.Wurblet.

The dependency above not only provides this interface but also 2 abstract classes to make the developer’s life easier:

org.wurbelizer.wurblet.AbstractWurblet that implements org.wurbelizer.wurblet.Wurblet
org.wurbelizer.wurblet.AbstractJavaWurblet that extends org.wurbelizer.wurblet.AbstractWurblet

To define the properties of the DTO we need some model which can be parsed by the wurblet. For this tutorial we’re using a very simple format with one line per property consisting of:

the Java type, e.g. String
the property’s name
some optional comment

In src/main/java/com/example/wurblets please create file DTOWurblet.java with the following content:

package com.example.wurblets;

import org.wurbelizer.wurbel.WurbelException;
import org.wurbelizer.wurbel.WurbelHelper;
import org.wurbelizer.wurblet.AbstractJavaWurblet;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

/**
 * Base class for the {@code @DTO}-wurblet.
 */
public class DTOWurblet extends AbstractJavaWurblet {

  /**
   * DTO property.
   */
  protected class Property {

    private final String type;                // the java type
    private final String name;                // the property name
    private final String comment;             // the comment

    public Property(String type, String name, String comment) {
      this.type = type;
      this.name = name;
      this.comment = comment == null || comment.isEmpty() ? "the " + name + " property" : comment.trim();
    }

    public String getType() {
      return type;
    }

    public String getName() {
      return name;
    }

    public String getComment() {
      return comment;
    }

    public String getGetterName() {
      return ("boolean".equals(type) ? "is" : "get") + firstToUpper(name);
    }
  }

  protected String filename;            // filename of the here-doc holding the model
  protected List<Property> properties;  // the DTO properties

  @Override
  public void run() throws WurbelException {
    super.run();

    if (getContainer().getArgs().length == 0) {
      throw new WurbelException("usage: @wurblet <guardname> DTO <filename>");
    }
    filename = getContainer().getArgs()[0];

    properties = new ArrayList<>();

    try (BufferedReader reader = new BufferedReader(WurbelHelper.openReader(filename))) {
      String line;
      while ((line = reader.readLine()) != null) {
        line = line.trim();
        if (!line.isEmpty() && !line.startsWith("#")) {
          StringTokenizer stok = new StringTokenizer(line);
          String type = null;
          String name = null;
          StringBuilder comment = new StringBuilder();
          while (stok.hasMoreTokens()) {
            String token = stok.nextToken();
            if (type == null) {
              type = token;
            }
            else if (name == null) {
              name = token;
            }
            else {
              if (comment.length() > 0) {
                comment.append(' ');
              }
              comment.append(token);
            }
          }
          if (type == null || name == null) {
            throw new WurbelException("property line too short: '" + line + "'");
          }
          properties.add(new Property(type, name, comment.toString()));
        }
      }

      // validate
      for (Property property : properties) {
        if (property.getType().isEmpty()) {
          throw new WurbelException("missing property type");
        }
        if (property.getName().isEmpty()) {
          throw new WurbelException("missing property name");
        }
      }
    }
    catch (IOException ex) {
      throw new WurbelException("reading model " + filename + " failed", ex);
    }
  }

  private String firstToUpper(String str) {
    return str.substring(0, 1).toUpperCase() + str.substring(1);
  }
}

Next, in src/main/wurblets/com/example/wurblets create the file DTO.wrbl with the following content:

@{package com.example.wurblets}@
@{import java.util.*}@
@{import java.io.*}@
@{import org.wurbelizer.wurbel.*}@
@{import org.wurbelizer.wurblet.*}@
@{import org.wurbelizer.misc.*}@
@{extends DTOWurblet}@
@{args}@
@{comment
Creates code for a data transfer object.
}@
@[
  private void wurbel() throws WurbelException {

    // create declarations
    for (Property property: properties) {
]@
  private final @(property.getType())@ @(property.getName())@;  // @(property.getComment())@
@[
    }

    // create constructor
]@

  /**
   * Creates a @(getClassName())@.
   *
@[
    StringBuilder args = new StringBuilder();
    for (Property property: properties) {
      if (args.length() > 0) {
        args.append(", ");
      }
      args.append(property.getType()).append(' ').append(property.getName());
]@
   * \@param @(property.getName())@ @(property.getComment())@
@[
    }
]@
   */
  public @(getClassName())@(@(args)@) {
@[
    for (Property property: properties) {
]@
    this.@(property.getName())@ = @(property.getName())@;
@[
    }
]@
  }
@[

    // create getter
    for (Property property: properties) {
]@

  /**
   * Gets @(property.getComment())@.
   *
   * \@return @(property.getComment())@
   */
  public @(property.getType())@ @(property.getGetterName())@() {
    return @(property.getName())@;
  }
@[
    }
  }
]@

As already mentioned in the introduction the wurbelizer’s template language is Java with a few syntax extensions. The extensions are necessary to separate the template level from the generated code level:

@[ to switch to template level
]@ to switch to code level
@(...)@ to extract a value from the template level (within code level)

The other lines at the beginning of the wurblet source are pretty self-explaining. Notice that the wurblet extends DTOWurblet.

Execute mvn clean install in the parent directory. This will invoke the wurbiler (wurblet compiler), compile the Java code and create a jar file.

In the next chapter we will use the wurblet to generate code for a DTO.

← Prerequisites Generate Code →