CompletableFuture is a class in Java that allows you to write asynchronous, non-blocking code using a fluent API. Here are the steps to use CompletableFuture in Java:
- Create a CompletableFuture object:
CompletableFuture<Integer> completableFuture = new CompletableFuture<>();
- Supply a function that will be executed asynchronously to the CompletableFuture object. The function can be supplied using the supplyAsync method:
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
// Perform some expensive computation
return 42;
});
- Chain multiple functions together using the thenApply method. The thenApply method takes a Function as an argument, and returns a new CompletableFuture object:
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
// Perform some expensive computation
return 42;
}).thenApply(result -> {
// Process the result of the expensive computation
return result * 2;
});
- You can also chain multiple functions together using the thenCompose method. The thenCompose method takes a Function that returns a CompletableFuture as an argument:
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
// Perform some expensive computation
return 42;
}).thenCompose(result -> CompletableFuture.supplyAsync(() -> {
// Perform another expensive computation using the result of the first computation
return result * 2;
}));
- Use the join method to block the current thread and wait for the CompletableFuture to complete:
int result = completableFuture.join();
Alternatively, you can use the get method, which throws a checked exception if the CompletableFuture completes exceptionally:
int result = completableFuture.get();
- Handle exceptions using the exceptionally method. The exceptionally method takes a Function that handles the exception and returns a default value:
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
// Perform some expensive computation
throw new RuntimeException(“Something went wrong”);
}).exceptionally(ex -> {
// Handle the exception and return a default value
return -1;
});
That’s it! You can use these basic steps to write complex asynchronous code using CompletableFuture in Java.