mybatis源码parsing包--PropertyParser文档解析中的变量替换

mybatis中对占位符替换成实际的变量值用到的就是PropertyParser类。例如 select * from tb where id = #{id} 需要替换成 select * from tb where id = 123

 

PropertyParser的parse方法实际上使用了GenericTokenParser 的parser方法，下面分析下GenericTokenParser的parser方法

其中GenericTokenParser类中有如下三个属性

以 SELECT * FROM t_action WHERE `id`=#{id} and name = #{name} ORDER BY `actionTime`  openToken就是 “#{”  closeToken 就是 “ } ”

下面这段代码干了这么个事：

把传入的sql模板转成字符数组，builder用来存储最终的sql，先截取 SELECT * FROM t_action WHERE `id`=  存到 builder然后截取出 id，然后调用TokenHandler的handleToken方法获取id的实际值再拼到builder后边，比如id实际值是123 这时builder就得到 SELECT * FROM t_action WHERE `id`=123 ，依次类推把sql模板中的所有占位符都替换掉。

  /**
   *
   * @param text 输入：
   *             SELECT * FROM t_action
   *          WHERE `id`=#{id} and name = #{name}
   *         ORDER BY `actionTime`
   *
   * @return 输出：
   *          SELECT * FROM t_action
   *          WHERE `id`=？ and name = ？
   *         ORDER BY `actionTime`
   */
  public String parse(String text) {
    if (text == null || text.isEmpty()) {
      return "";
    }
    // search open token
    int start = text.indexOf(openToken);
    if (start == -1) {
      return text;
    }
    char[] src = text.toCharArray();
    int offset = 0;
    final StringBuilder builder = new StringBuilder();
    //表达式 例如 #{name} 中的name
    StringBuilder expression = null;
    while (start > -1) {
      if (start > 0 && src[start - 1] == '\\') {
        // this open token is escaped. remove the backslash and continue.
        builder.append(src, offset, start - offset - 1).append(openToken);
        offset = start + openToken.length();
      } else {
        // found open token. let's search close token.
        if (expression == null) {
          expression = new StringBuilder();
        } else {
          expression.setLength(0);
        }
        builder.append(src, offset, start - offset);
        offset = start + openToken.length();
        int end = text.indexOf(closeToken, offset);
        while (end > -1) {
          if (end > offset && src[end - 1] == '\\') {
            // this close token is escaped. remove the backslash and continue.
            expression.append(src, offset, end - offset - 1).append(closeToken);
            offset = end + closeToken.length();
            end = text.indexOf(closeToken, offset);
          } else {
            expression.append(src, offset, end - offset);
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(src, start, src.length - start);
          offset = src.length;
        } else {
          // 这里调用了传入的handler的方法
          builder.append(handler.handleToken(expression.toString()));
          offset = end + closeToken.length();
        }
      }
      start = text.indexOf(openToken, offset);
    }
    if (offset < src.length) {
      builder.append(src, offset, src.length - offset);
    }
    return builder.toString();
  }