Java - 发送到 OutputStream 的两个字符串之间的差异

Question

• 我将 2 个字符串值从 Client.java 发送到 OutputStream，如下所示:

  outputStream.write(username.getText().getBytes());
  outputStream.write(password.getText().getBytes());
  

• 在 Server.java 中，当我读取 inputStream 时，我试图将每个值分开:

  inputStream = s.getInputStream();
byte[]用户名 = 新字节[20];
inputStream.read(用户名);
String user = new String(用户名);
System.out.println("用户名 = "+user);

我逻辑上得到:usernamepassword 作为控制台输出。我想做的是:

     String usr = new String(user);
     String pass = new String(password);

有没有比在输出流字符串中添加一些分隔符更好的方法？

Answer 1

您需要分隔两个字符串值，以便读者知道一个字符串在哪里结束以及下一个字符串在哪里开始。该分隔符的实际组成由您根据您的特定需求决定。

1. 您可以使用固定宽度整数写出字符串的字节长度，然后再写出实际字节。然后，读取器可以先读取长度，然后再读取后面指定的字节数:

   DataOutputStream dos = new DataOutputStream(outputStream);
   byte[] bytes;
   int len;
   
   bytes = username.getText().getBytes(StandardCharsets.UTF_8);
   len = bytes.length;
   dos.writeInt(len);
   dos.write(bytes, 0, len);
   
   bytes = password.getText().getBytes(StandardCharsets.UTF_8);
   len = bytes.length;
   dos.writeInt(len);
   dos.write(bytes, 0, len);
   

   inputStream = s.getInputStream();
   DataInputStream dis = new DataInputStream(inputStream);
   byte[] bytes;
   int len;
   
   len = dis.readInt();
   bytes = new byte[len];
   dis.readFully(bytes);
   String username = new String(bytes, StandardCharsets.UTF_8);
   
   len = dis.readInt();
   bytes = new byte[len];
   dis.readFully(bytes);
   String password = new String(bytes, StandardCharsets.UTF_8);
   

   或者，DataOutputStream 和 DataInputStream 可以直接写入/读取 String 值，在内部为您处理上述逻辑(使用 Short 而不是 int 来表示长度值):

   DataOutputStream dos = new DataOutputStream(outputStream);
   dos.writeUTF(username.getText());
   dos.writeUTF(password.getText());
   

   inputStream = s.getInputStream();
   DataInputStream dis = new DataInputStream(inputStream);
   
   String username = dis.readUTF();
   String password = dis.readUTF();
   

2. 您可以写出一个永远不会出现在字符串值本身中的唯一字符序列，例如换行符或控制字符(甚至是空终止符)。然后，读取器可以读取字节，直到遇到该序列:

   OutputStreamWriter writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8); 
   String s;
   
   s = username.getText();
   writer.write(s, 0, s.length());
   writer.write(10);
   
   s = password.getText();
   writer.write(s, 0, s.length());
   writer.write(10);
   

   inputStream = s.getInputStream();
   BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
   
   String username = reader.readLine();
   String password = reader.readLine();
   

   或者:

   OutputStreamWriter writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8); 
   String s;
   
   s = username.getText();
   writer.write(s, 0, s.length());
   writer.write(0);
   
   s = password.getText();
   writer.write(s, 0, s.length());
   writer.write(0);
   

   inputStream = s.getInputStream();
   BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
   StringBuilder sb = new StringBuilder();
   int ch;
   
   do
   {
       ch = reader.read();
       if (ch <= 0) break;
       sb.append((char)ch);
   }
   while (true);
   String username = sb.toString();
   
   sb.setLength(0);
   do
   {
       ch = reader.read();
       if (ch <= 0) break;
       sb.append((char)ch);
   }
   while (true);
   String password = sb.toString();