Java利用PushbackReader实现返回对文本中的指定字符串之前的内容

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

public class PushbackTest {
    public static void main(String[] args) {
        try(PushbackReader pr = new PushbackReader(new FileReader("src/com/ming/test/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());
                    char tmp[] = new char[targetIndex];
                    pr.read(tmp,0,targetIndex);
                    System.out.print(new String(tmp,0,targetIndex));
                    System.exit(0);
                }else{
                    System.out.print(lastContent);
                    lastContent = content;
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

输出
package com.ming.test;

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

public class PushbackTest {
    public static void main(String[] args) {
        try(PushbackReader pr =