JarCasting
java-predicates
collection of predefined predicates for all basic types
Maven
Release artifact
<dependency>
<groupId>io.github.codejanovic</groupId>
<artifactId>java-predicates</artifactId>
<version>0.1.0</version>
</dependency>
Snapshot artifact
<dependency>
<groupId>io.github.codejanovic</groupId>
<artifactId>java-predicates</artifactId>
<version>0.2.0-SNAPSHOT</version>
</dependency>
Motivation
The motivation behind this project is to achieve a more readable and maintainable way of chaining checks on all kind of basic types (primitives, strings, arrays, etc ) we use in our everyday code, by providing predefined Predicate<T> implementations.
So lets be naive and try to check that a given String conforms to a valid .de and .com URL.
public void doSomethingWhenUrlIsValid(final String url) {
if (url != null
&& !url.isEmpty()
&& url.startsWith("http://")
&& (url.endsWith(".de") || url.endsWith(".com"))) {
doSomethingWithThatUrl();
} else {
throw new IllegalArgumentException("invalid url: " + url);
}
}
Basically this code has two issues, a major and a minor one. the major one is that whenever the condition on what a valid URL is changes, you have to change the if statement. the minor one is that its not as fluent as it could be for the reader.
Now lets use a separate method and the Predicate<T> interface from Java 8 to fix our major issue ...
public void doSomethingWhenUrlIsValid(final String url) {
if (isValidUrl().test(url)) {
doSomethingWithThatUrl();
} else {
throw new IllegalArgumentException("invalid url: " + url);
}
}
public Predicate<String> isValidUrl() {
return string -> string != null
&& !string.isEmpty()
&& string.startsWith("http://")
&& (string.endsWith(".de") || string.endsWith(".com"));
}
... and rewrite isValidUrl() method using our fluent Predicates interface ...
public Predicate<String> isValidUrl() {
final Predicates checking = new Predicates.Default();
final StringPredicates it = checking.string();
return checking.that().valid().when().string().isNotNull()
.and(it.isNotEmpty())
.and(it.startsWith("http://"))
.and(it.endsWith(".de").or(it.endsWith(".com")));
}