/**
     * 读流生成byte[]，全读取
     * 
     * @param is
     * @return
     */
    public static byte[] readFully(InputStream is) {
        byte[] bytes = null;
        if (is != null) {
            try {
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                int l = 0;
                byte[] b = new byte[1024];
                while ((l = is.read(b)) != -1) {
                    baos.write(b, 0, l);
                }
                bytes = baos.toByteArray();
                baos.close();
                baos = null;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return bytes;
    }

------解决方案--------------------
ByteArrayOutputStream baos = new ByteArrayOutputStream();  
System.out.println("baos=="+baos); 

这时候还没往里头写数据呢，当然是空的...
你要根据返回的byte[]是不是空来判断有没有数据


------解决方案--------------------
byte[] bstr=readFully(is);
str=new String(bstr,"UTF-8");  
System.out.println("str=="+str);