读取源文件内容的每一行,求和再存入最后一行

要求如下：

读取源文件内容的每一行,求和再存入最后一行

代码如下：

public class TestDemo7 {
	public static void main(String[] args) {
		System.out.println("*****开始****");
		try{
			FileInputStream fis = new FileInputStream("pw.txt");
			InputStreamReader isr = new InputStreamReader(fis,"GBK");
			BufferedReader br = new BufferedReader(isr);
			StringBuilder builder = new StringBuilder();
			String str = null;
			while( (str = br.readLine())!= null ){
				builder.append(str);
			}
			//追加写
			FileOutputStream fos = new FileOutputStream("pw.txt",true);
			fos.write(builder.toString().getBytes("GBK"));
			br.close();
			fos.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println("*****结束****");
	}
}
           

或者：

public class TestDemo7 {
	public static void main(String[] args) {
		System.out.println("*****开始****");
		try{
			BufferedReader br = 
				new BufferedReader(
					new InputStreamReader(
						new FileInputStream("pw.txt"),"GBK"));
			StringBuilder builder = new StringBuilder();
			String str = null;
			while( (str = br.readLine())!= null ){
				builder.append(str);
			}
			//追加写
			FileOutputStream fos = new FileOutputStream("pw.txt",true);
			fos.write(builder.toString().getBytes("GBK"));
			br.close();
			fos.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println("*****结束****");
	}
}
           

原文件pw.txt中为：

大家好!
hello!
bye!
           

程序运行后文件内容为:

大家好!
hello!
bye!
大家好!hello!bye!