XMLIncludeTransformer.java

/*
 * Copyright 2012 MyBatis.org.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.ibatis.builder.xml;

import org.apache.ibatis.builder.IncompleteElementException;
import org.apache.ibatis.builder.MapperBuilderAssistant;
import org.apache.ibatis.parsing.PropertyParser;
import org.apache.ibatis.parsing.XNode;
import org.apache.ibatis.session.Configuration;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * @author Frank D. Martinez [mnesarco]
 */
/**
 * XML include转换器
 *
 */
public class XMLIncludeTransformer {

  private final Configuration configuration;
  private final MapperBuilderAssistant builderAssistant;

  public XMLIncludeTransformer(Configuration configuration, MapperBuilderAssistant builderAssistant) {
    this.configuration = configuration;
    this.builderAssistant = builderAssistant;
  }

//<select id="selectUsers" resultType="map">
//  select <include refid="userColumns"/>
//  from some_table
//  where id = #{id}
//</select>
  public void applyIncludes(Node source) {
    if (source.getNodeName().equals("include")) {
      //走到这里，单独解析<include refid="userColumns"/>
      //拿到SQL片段
      Node toInclude = findSqlFragment(getStringAttribute(source, "refid"));
      //递归调用自己,应用上?
      applyIncludes(toInclude);
      //总之下面就是将字符串拼接进来，看不懂。。。
      if (toInclude.getOwnerDocument() != source.getOwnerDocument()) {
        toInclude = source.getOwnerDocument().importNode(toInclude, true);
      }
      source.getParentNode().replaceChild(toInclude, source);
      while (toInclude.hasChildNodes()) {
        toInclude.getParentNode().insertBefore(toInclude.getFirstChild(), toInclude);
      }
      toInclude.getParentNode().removeChild(toInclude);
    } else if (source.getNodeType() == Node.ELEMENT_NODE) {
        //一开始会走这段，取得所有儿子
      NodeList children = source.getChildNodes();
      for (int i=0; i<children.getLength(); i++) {
          //递归调用自己
        applyIncludes(children.item(i));
      }
    }
  }

  private Node findSqlFragment(String refid) {
    refid = PropertyParser.parse(refid, configuration.getVariables());
    refid = builderAssistant.applyCurrentNamespace(refid, true);
    try {
      //去之前存到内存map的SQL片段中寻找
      XNode nodeToInclude = configuration.getSqlFragments().get(refid);
      //clone一下，以防改写？
      return nodeToInclude.getNode().cloneNode(true);
    } catch (IllegalArgumentException e) {
      throw new IncompleteElementException("Could not find SQL statement to include with refid '" + refid + "'", e);
    }
  }

  private String getStringAttribute(Node node, String name) {
    return node.getAttributes().getNamedItem(name).getNodeValue();
  }
}