Use jOOλ’s Sneaky Throw to Avoid Checked Exceptions

Don’t you hate how you have to wrap checked exception throwing code in static initialisers? E.g. you cannot write this in Java:

public class Test {
    static final Class<?> klass = Class.forName("org.h2.Driver");
}

There’s an unhandled ClassNotFoundException, and you can’t catch / rethrow it simply. A static initialiser is needed:

public class Test {
    static final Class<?> klass;

    static {
        try {
            klass = Class.forName("org.h2.Driver");
        }
        catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
}

Yuck.

Luckily, one of jOOλ’s lesser known features is the Sneaky class, which contains a bunch of utility methods that wrap a JDK functional interface to an equivalent, “sneaky-throwing” functional interface that doesn’t declare the checked exception.

In short, you can write:

public class Test {
    static final Class<?> klass = Sneaky.supplier(
        () -> Class.forName("org.h2.Driver")
    ).get();
}

The exception is simply re-thrown “sneakily”, as the JVM doesn’t care about an exception’s checked-ness. If you don’t have H2 on your classpath, you’ll get:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ClassNotFoundException: org.h2.Driver
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
        at java.base/java.lang.Class.forName0(Native Method)
        at java.base/java.lang.Class.forName(Class.java:375)
        at org.jooq.test.util.Test.lambda$0(Test.java:44)
        at org.jooq.lambda.Unchecked.lambda$supplier$38(Unchecked.java:1695)
        at org.jooq.test.util.Test.<clinit>(Test.java:44)

You can use this approach wherever else a JDK functional interface is required, and you don’t care about an exception’s checked-ness, e.g. in streams:

// Doesn't compile:
Stream
    .generate(
        () -> Class.forName("org.h2.Driver"))
    .limit(1)
    .forEach(System.out::println);

// So ugly
Stream
    .generate(
        () -> {
            try {
                return Class.forName("org.h2.Driver");
            }
            catch (ClassNotFoundException e) {
                throw new RuntimeException(e);
            }
        })
    .limit(1)
    .forEach(System.out::println);

// Use jOOλ's Sneaky supplier
Stream
    .generate(Sneaky.supplier(
        () -> Class.forName("org.h2.Driver")))
    .limit(1)
    .forEach(System.out::println);

Get jOOλ here: https://github.com/jOOQ/jOOL

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