BuilderPattern.java

import java.util.ArrayList;
import java.util.Collections;

class HtmlElement
{
  public String name, text;
  public ArrayList<HtmlElement> elements = new ArrayList<HtmlElement>();
  private final int indentSize = 2;
  private final String newLine = System.lineSeparator();

  public HtmlElement()
  {
  }

  public HtmlElement(String name, String text)
  {
    this.name = name;
    this.text = text;
  }

  private String toStringImpl(int indent)
  {
    StringBuilder sb = new StringBuilder();
    String i = String.join("", Collections.nCopies(indent * indentSize, " "));
    sb.append(String.format("%s<%s>%s", i, name, newLine));
    if (text != null && !text.isEmpty())
    {
      sb.append(String.join("", Collections.nCopies(indentSize*(indent+1), " ")))
        .append(text)
        .append(newLine);
    }

    for (HtmlElement e : elements)
      sb.append(e.toStringImpl(indent + 1));

    sb.append(String.format("%s</%s>%s", i, name, newLine));
    return sb.toString();
  }

  @Override
  public String toString()
  {
    return toStringImpl(0);
  }
}

class HtmlBuilder
{
  private String rootName;
  private HtmlElement root = new HtmlElement();

  public HtmlBuilder(String rootName)
  {
    this.rootName = rootName;
    root.name = rootName;
  }

  // not fluent
  public void addChild(String childName, String childText)
  {
    HtmlElement e = new HtmlElement(childName, childText);
    root.elements.add(e);
  }

  public HtmlBuilder addChildFluent(String childName, String childText)
  {
    HtmlElement e = new HtmlElement(childName, childText);
    root.elements.add(e);
    return this;
  }

  public void clear()
  {
    root = new HtmlElement();
    root.name = rootName;
  }

  // delegating
  @Override
  public String toString()
  {
    return root.toString();
  }
}

class BuilderDemo
{
  public static void main(String[] args)
  {
    // we want to build a simple HTML paragraph
    System.out.println("Testing");
    String hello = "hello";
    StringBuilder sb = new StringBuilder();
    sb.append("<p>")
      .append(hello)
      .append("</p>"); // a builder!
    System.out.println(sb);

    // now we want to build a list with 2 words
    String [] words = {"hello", "world"};
    sb.setLength(0); // clear it
    sb.append("<ul>\n");
    for (String word: words)
    {
      // indentation management, line breaks and other evils
      sb.append(String.format("  <li>%s</li>\n", word));
    }
    sb.append("</ul>");
    System.out.println(sb);

    // ordinary non-fluent builder
    HtmlBuilder builder = new HtmlBuilder("ul");
    builder.addChild("li", "hello");
    builder.addChild("li", "world");
    System.out.println(builder);

    // fluent builder
    builder.clear();
    builder.addChildFluent("li", "hello")
      .addChildFluent("li", "world");
    System.out.println(builder);
  }
}