例如，我的程序中有个字符串变量String s,变量s存储的信息是一个例如如下的xml数据：
<book>
       <bookid>1</bookid>
 <Author>abc</Author>
       <bookname>数学</bookname>
       <exception>some text2</exception>
</book>
<book>
       <bookid>1</bookid>
 <Author>asdfbc</Author>
       <bookname>数学2</bookname>
       <exception>some text</exception>
</book>
<book>
       <bookid>3</bookid>
 <Author>aadfbc</Author>
       <bookname>数学3</bookname>
       <exception>some text3</exception>
</book>
<book>
       <bookid>4</bookid>
 <Author>abc</Author>
       <bookname>数学4</bookname>
       <exception>some text4</exception>
</book>

现在，我想如何通过从这个字符串变量s中查询符合条件是author='abc'的纪录，最后查询后的结构保留以前的xml格式，如下
<book>
       <bookid>1</bookid>
 <Author>abc</Author>
       <bookname>数学</bookname>
       <exception>some text2</exception>
</book>
<book>
       <bookid>4</bookid>
 <Author>abc</Author>
       <bookname>数学4</bookname>
       <exception>some text4</exception>
</book>
将上面的结果再传递给另一个字符串变量s1?
3x！！！