How to interpret string as a negative number or zero and throw IAE accordingly?

Question

I have a method in which I am accepting a String and that can be number as a string or a normal string.

public Builder setClientId(String clientId) {
    checkNotNull(clientId, "clientId cannot be null");
    checkArgument(clientId.length() > 0, "clientId can't be an empty string");
    this.clientId = clientId;
    return this;
}

Now I want to add a check let's say if anyone is passing clientId as negative number "-12345" or zero "0", then I want to interpret this and throw IllegalArgumentException with message as "clientid must not be negative or zero as a number" or may be some other good message. How can I do this using guava Preconditions if possible?

As per suggestion I am using below code:

public Builder setClientId(String clientId) {
    checkNotNull(clientId, "clientId cannot be null");
    checkArgument(clientId.length() > 0, "clientId can't be an empty string");
    checkArgument(!clientid.matches("-\\d+|0"), "clientid must not be negative or zero");
    this.clientId = clientId;
    return this;
}

Is there any better way of doing it?

Answer 1

I think the simplest way of doing this is as follows:

 public Builder setClientId(String clientId) {
    final Integer id = Ints.tryParse(clientId);
    checkArgument(id != null && id.intValue() > 0,
      "clientId must be a positive number, found: '%s'.", clientId);
    this.clientId = clientId;
    return this;
  }

When calling this method, this gives:

.setClientId("+-2"); 
// java.lang.IllegalArgumentException: clientId must be a positive number, found: '+-2'.

.setClientId("-1"); 
// java.lang.IllegalArgumentException: clientId must be a positive number, found: '-1'.

.setClientId(null); 
// java.lang.NullPointerException

This code uses Ints.tryParse. From the JavaDoc:

Returns:

the integer value represented by string, or null if string has a length of zero or cannot be parsed as an integer value

Also, it throws a NullPointerException when a null is received.

---

Edit: however, if any other string is allowed, the code changes to:

public Builder setClientId(String clientId) {
    checkArgument(!Strings.isNullOrEmpty(clientId),
      "clientId may not be null or an empty string, found '%s'.", clientId);
    final Integer id = Ints.tryParse(clientId);
    if (id != null) {
      checkArgument(id.intValue() > 0,
        "clientId must be a positive number, found: '%s'.", clientId);
    }
    this.clientId = clientId;
    return this;
  }

This code will accept all strings that are either a strictly positive integer OR non-null and non-empty.