Java Output流写入包装问题

 ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(byteArrayOutputStream);


        int size = byteArrayOutputStream.size();
        System.out.println("写入之前为:" + size);


        outputStreamWriter.write("我是一个魔鬼");
//        outputStreamWriter.flush();
//        outputStreamWriter.close();
        int size1 = byteArrayOutputStream.size();
        System.out.println("写入之后为:" + size1);

当这样执行时，输出前后都为0，这是因为 

OutputStreamWriter 相当于包装了一层，并没有给

ByteArrayOutputStream对象写入内容，需要

OutputStreamWriter 调用flush()或close()方法即可