Java转换流 无输出内容

Question

运行后，newTest文件中无任何内容，无报错。
是我哪里有问题吗？

import java.io.*;

public class StreamTest {
    public static void main(String[] args) {
        FileInputStream fis;
        InputStreamReader inputStreamReader = null;
        FileOutputStream outputStream;
        OutputStreamWriter outputStreamWriter = null;
        try {
            fis = new FileInputStream("D://Test.txt");
            inputStreamReader = new InputStreamReader(fis);
            outputStream = new FileOutputStream("D://newTest.txt");
            outputStreamWriter = new OutputStreamWriter(outputStream);
            char[] arr = new char[1024];
            int len = 0;
            while ((len = inputStreamReader.read(arr, 0, len)) > 0) {
                outputStreamWriter.write(arr, 0, len);
            }
            System.out.println(len);//运行后输出0
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (inputStreamReader != null) {
                    inputStreamReader.close();
                }
                if (outputStreamWriter != null) {
                    outputStreamWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 1

int len = 0;
while ((len = inputStreamReader.read(arr, 0, len)) > 0)

这样写是不满足循环条件的，len初始就是0，等价于read(arr, 0, 0)从0位置读取0个字符吗，结果怎么会大于0？
修改如下：

while ((len = inputStreamReader.read(arr, 0, 1024)) > 0)

或者

while ((len = inputStreamReader.read(arr))!=-1)

完整代码如下：

import java.io.*;
public class Main {
    public static void main(String[] args){
        FileInputStream fis;
        InputStreamReader inputStreamReader = null;
        FileOutputStream outputStream;
        OutputStreamWriter outputStreamWriter = null;
        try {
            fis = new FileInputStream("D://Test.txt");
            inputStreamReader = new InputStreamReader(fis);
            outputStream = new FileOutputStream("D://newTest.txt");
            outputStreamWriter = new OutputStreamWriter(outputStream);
            char[] arr = new char[1024];
            int len = 0;
            while ((len = inputStreamReader.read(arr))!=-1) {
                outputStreamWriter.write(arr);
                outputStreamWriter.flush();   //每次写完记得flush，刷新缓存区的内容
            }
            System.out.println(len);//运行后输出0
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (inputStreamReader != null) {
                    inputStreamReader.close();
                }
                if (outputStreamWriter != null) {
                    outputStreamWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}