String Utils - Java

Question

I've created a StringUtil class which is used for some string validation across the application. The code for the StringUtil is as below,

public class StringUtil {
    public static synchronized boolean isValidString(String string) {
        return string!= null && string.trim().length() > 0;
    }

}

In this class the method checks whether the string is a valid string or not. This method is thread safe. In an enterprise application, there might be multiple threads accessing this method. If a thread is accessing this method, then all the other threads have to wait for its turn. This method in turn will be used very frequently to check the string for null values. So which is the best option

Making this a singleton and thread safety
Making this as instance method
Is there are any other way to organize a pool with objects of this type and each thread would pick up one and release the object to the pool once done.So thread safety is not a concern and object creation is also not done.
Are are there any open source libraries for the same.

so "" is not a valid String in your application ? I'd go for isEmpty /notEmpty methods, who knows when "" will become a valid string anyway... — BigMike
– BigMike, Commented Sep 14, 2012 at 8:33
I agree string are immutable. If two thread call these simultaneous with a null and a valid string on the other, then how thread safety issues would be solved? — vvekselva
– vvekselva, Commented Sep 14, 2012 at 8:35
...and the method probably deserves a rename too. "" is in fact a valid string (in the context of your use-case probably not). How about isPresent or isNotEmpty? — Matt
– Matt, Commented Sep 14, 2012 at 8:39
Since this is class method, multiple threads would call only like this (I assume) StringUtil.isValidString(null)(Thread1) StringUtil.isValidString("SampleString")(Thread2) Here the state is not shared, the method is shared. Then how we would solve the thread safety issues. — vvekselva
– vvekselva, Commented Sep 14, 2012 at 8:43
well actually is not only a class method, it's a static class method. It's planned to be used without allocating a new object by design, the synchronized is just overkill — BigMike
– BigMike, Commented Sep 14, 2012 at 9:37

Keppil · Accepted Answer · 2012-09-14 08:28:59Z

16

Since you don't have any state here (you only use the method argument string), the method is inherently thread safe. Therefore there is no need to use the synchronized keyword.

If the method is used throughout your project, just declaring it static as you have already done is the best option.

answered Sep 14, 2012 at 8:28

Keppil

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Augusto · Accepted Answer · 2012-09-14 08:31:36Z

7

Usually helper methods like this, are public static, and not synchronized, because the class doesn't hold state. Since it doesn't hold state neither, you don't need a pool.

I think a good example of this the apache commons StringUtils class.

I have the feeling that you're trying to use a neutron cannon to open a walnut, simplicity is king :)

answered Sep 14, 2012 at 8:31

Augusto

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davek · Accepted Answer · 2012-09-14 08:30:52Z

3

You could try the util classes from Apache Commons.

But you have thread-safety here anyway, since you're not manipulating anything in the class that other calls might read (i.e. you have no state).

answered Sep 14, 2012 at 8:30

davek

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basiljames · Accepted Answer · 2012-09-14 08:32:10Z

3

You should probably use the StringUtils class in Apache Commons.

answered Sep 14, 2012 at 8:32

basiljames

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2 Comments

gigadot Over a year ago

StringUtils.isBlank() in apache common is probably what he wants.

Lyrion Over a year ago

@gigadot StringUtils.isNotBlank() is what he needs/wants

AlexR · Accepted Answer · 2012-09-14 08:31:59Z

1

This method should not be synchronized because it does not use any class level variables. So multiple threads can concurrently access it without any problem.

Moreover forget about synchronization when you are writing code for enterprise application that is running into container. It is container's responsibility to care about thread safety. synchronized blocks just bother the container to do its job. If you need synchronization in enterprise application re-think your design and/or find other patters (there are a lot) to solve your problem.

answered Sep 14, 2012 at 8:31

AlexR

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1 Comment

Brian Agnew Over a year ago

I'm not convinced about your 'forget' statement. It's possible to have shared state in a container, and/or to spawn separate threads against shared state.

Amit Deshpande · Accepted Answer · 2012-09-14 09:03:10Z

1

There is no need of synchronized keyword since String is immutable object

Immutable objects are often useful because they are inherently thread-safe

public static boolean isValidString(String string) {
    return !(string== null || string.isEmpty()); //Since 1.6
}

answered Sep 14, 2012 at 9:03

Amit Deshpande

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Lorand Bendig · Accepted Answer · 2012-09-14 09:14:53Z

1

Utility classes usually contain only static methods therefore it always a good idea to state explicitly that these classes were not designed to be instantiated. Therefore make their constructor private:

public class StringUtils {

  private StringUtils() {
    throw new AssertionError("shouldn't be instantiated");
  }

}

(see Joshua Bloch's Bible : Item 4: Enforce noninstantiability with a private constructor )

answered Sep 14, 2012 at 9:14

Lorand Bendig

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