Jwt校验IP合法性（大学时的练习，不严谨）

```java
  public static boolean judgeIP(JTextField ipText, JFrame jf)  {
    String ipAddress = ipText.getText();
    
    String[] ip = ipAddress.split("\\.");
    if (ip.length != 4) {
      return false;
    }
    for (int i = 0; i < 4; i++)
    {
      int dress = 0;
      try
      {
        dress = Integer.parseInt(ip[i]);
      }
      catch (NumberFormatException e1)
      {
        return false;
      }
      if ((dress >= 0) && (dress <= 255))
      {
        if (i == 3)
        {
          System.out.println("IP地址【" + ipAddress + "】合法");
          return true;
        }
      }
      else {
        return false;
      }
    }
    return false;
  }
```

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## 校验子网掩码

```java
// (子网掩码，所属ip分类)  
public static boolean judgeMark(String subMark, String ipCategory)
  {
    String[] split = subMark.split("\\.");
    
    String binartIp = "";
    for (int i = 0; i < 4; i++)
    {
      int parseInt = Integer.parseInt(split[i]);
      String str = MyToBinary.toBinary(parseInt);
      
      binartIp = binartIp + str;
      if (i < 3) {
        binartIp = binartIp + ".";
      }
    }
    int index0 = binartIp.indexOf("0");
    
    int index1 = binartIp.lastIndexOf("1");
    if (index0 < index1)
    {
      System.out.println("子网掩码【" + binartIp + "】非法");
      return false;
    }
    if (ipCategory.equals("A"))
    {
      if (Integer.parseInt(split[0]) != 255) {
        return false;
      }
    }
    else if (ipCategory.equals("B"))
    {
      if ((Integer.parseInt(split[0]) != 255) || (Integer.parseInt(split[1]) != 255)) {
        return false;
      }
    }
    else if (ipCategory.equals("C")) {
      if ((Integer.parseInt(split[0]) != 255) || (Integer.parseInt(split[1]) != 255) || (Integer.parseInt(split[2]) != 255)) {
        return false;
      }
    }
    System.out.println("子网掩码【" + binartIp + "】合法");
    
    return true;
  }
```