xtend lambda Extension methods

xtend.java

package org.eform.engine.core

import java.util.List
import org.eform.engine.api.FieldDefineItem
import org.eform.engine.api.FormDefineMetadata
import org.eform.engine.api.FormDefineMetadataParser
import org.jsoup.Jsoup
import org.jsoup.nodes.Document

import static extension com.google.common.base.Preconditions.*
import static extension com.google.common.collect.Iterators.*
import java.util.Iterator

class FormDefineMetadataParserImpl implements FormDefineMetadataParser{
  override FormDefineMetadata fromHtml(String html){
    Jsoup::parse(html).on[ doc |
    new FormDefineMetadataImpl(doc.formName).setFieldDefineItems(doc.fieldDefineItems)]
  }

  def private String getFormName(Document doc){
    doc.select("head title")?.first?.text
       .checkNotNull("表单名称不能为空")
  }
  
  def private List<? extends FieldDefineItem> getFieldDefineItems(Document doc){
    doc.select("body input").iterator
       .asList.map[ new FieldDefineItemImpl(it.attr("ng-model"))]
  }
  
  def private <T> List<T> asList(Iterator<T> iterator){
    val List<T> elements =  newArrayList()
    elements.addAll(iterator)
    elements
  }
  
  def private <T,R> R on(T t, (T) => R c){
    c.apply(t)
  }
}