gistfile1.java

public class VelocityWrapper {
  private final Template template;
  private final VelocityContext velocityContext;
  
  private VelocityWrapper(
        VelocityEngine velocityEngine,
        String templateLocation,
        VelocityContext velocityContext) {
          
    this.template = velocityEngine.getTemplate(templateLocation);
    this.velocityContext = velocityContext;
    
    generate();
  }

  public String generate() {
    StringWriter writer = new StringWriter();

    template.merge(velocityContext, writer);

    return writer.toString();
  }
    
  public static class Builder {
    private final VelocityEngine velocityEngine;
    private final String templateLocation;
    private final VelocityContext velocityContext = new VelocityContext();
      
    @Inject
    public Builder(VelocityEngine velocityEngine, @Assisted String templateLocation) {
      this.velocityEngine = velocityEngine;
      this.templateLocation = templateLocation;
    }
    
    public put(String key, String value) {
      velocityContext.put(key, value);
      
      return this;
    }
    
    public VelocityWrapper build() {
      return new VelocityWrapper(velocityEngine, templateLocation, velocityContext);
    }
  }
}

Then:

Builder builder = velocityWrapperBuilderFactory.create("path/to/my/velocity/file.vm");
builder.put("X", "Y");
builder.build(); // This will build and executed the velocity wrapper.

// Builder is consumed, a builder by definition shouldn't be reused and another one should be created through the factory.