利用PushbackReader读取文件中某个字符串之前的内容

package File;

import java.io.FileReader;
import java.io.IOException;
import java.io.PushbackReader;

/*读取文件中某个字符串之前的文件*/
//PushbackInputStream,PushbackReader应用

public class PushbackTest {
	public static void main(String[] args) {
		try(PushbackReader pr = new PushbackReader(new FileReader(
								"./src/File/PushbackTest.java"),64))
		{
			char[] buf = new char[32];
			String lastContent = "";
			int hasRead = 0;
			while((hasRead = pr.read(buf))>0)
			{
				String content = new String(buf,0,hasRead);
				int targetIndex = 0;

				if((targetIndex = (lastContent + content).indexOf("new PushbackReader"))>0)
				{
					pr.unread((lastContent+content).toCharArray());

					if(targetIndex>32)
					{
						buf = new char[targetIndex];
					}
					pr.read(buf,0,targetIndex);
					System.out.println(new String(buf,0,targetIndex));
					System.exit(0);
				}
				else
				{
					System.out.println(lastContent);
					lastContent = content;
				}
			}
		}catch(IOException ioe)
		{
			ioe.printStackTrace();
		}
	}
}