public static void main(String[] args) {
/** 例①： 打印数列的前10项 */
Stream<Long> fibonacci = Stream.generate(new FibonacciSupplier());
fibonacci.limit(10).forEach(System.out::println);
/** 例②： 打印数列的20~30项 */
Stream<Long> fibonacci2 = Stream.generate(new FibonacciSupplier());
List<Long> list = fibonacci2.skip(20).limit(10).collect(Collectors.toList());
list.forEach(System.out::println);
}
@Nullable
public static <T> T getIfSingle(@Nullable Stream<T> items) {
return items == null
? null
: items
.limit(2)
.map(Optional::ofNullable)
.reduce(
Optional.empty(), (a, b) -> a.isPresent() ^ b.isPresent() ? b : Optional.empty())
.orElse(null);
}
public static <T> void show(String title, Stream<T> stream) {
final int SIZE = 10;
List<T> firstElements = stream.limit(SIZE + 1).collect(Collectors.toList());
System.out.print(title + ": ");
if (firstElements.size() <= SIZE) System.out.println(firstElements);
else {
firstElements.remove(SIZE);
String out = firstElements.toString();
System.out.println(out.substring(0, out.length() - 1) + ", ...]");
}
}
public static void main(String[] args) {
S3BillingRecordFileScanner fileScanner = createBillingRecordFileScanner(args);
// The scan() method returns the full list of all billing files. This list could get rather
// large over time.
// For this example we'll just print a few files to demonstrate the method.
System.out.println("Printing a few billing files...");
try (Stream<S3BillingRecordFile> billingRecordFileStream = fileScanner.scan()) {
// For the purpose of this example we'll limit the output to 3 files. Java's streams make this
// trivial.
billingRecordFileStream
.limit(3)
.forEach(
s3BillingRecordFile -> {
printBillingRecoreFile(System.out, s3BillingRecordFile);
});
}
System.out.println();
// Scanning for all of the billing files has margin value as the contents of the various file
// types differs
// dramatically. It is likely that you are only interested in files of a particular type. The
// scan() method
// takes an argument that is the file type you are interested in.
System.out.println("Printing a few detailed line item files...");
try (Stream<S3BillingRecordFile> billingRecordFileStream =
fileScanner.scan(FileType.DETAILED_LINE_ITEMS)) {
// For the purpose of this example we'll limit the output to 3 files. Java's streams make this
// trivial.
billingRecordFileStream
.limit(3)
.forEach(
s3BillingRecordFile -> {
printBillingRecoreFile(System.out, s3BillingRecordFile);
});
}
System.out.println();
// If you are interested in a billing file for a specific month (ex. this month or last month)
// there
// is an additional overload of the scan() method that accepts a month and year.
System.out.println("Printing the detailed line item for Jan. 2016...");
try (Stream<S3BillingRecordFile> billingRecordFileStream =
fileScanner.scan(FileType.DETAILED_LINE_ITEMS, 2016, 1)) {
// Since we have specified the file type, year and month the scan() method above _should_
// return a stream
// with only zero or one items. We'll limit the results to 1 for sanity sake.
billingRecordFileStream
.limit(1)
.forEach(
s3BillingRecordFile -> {
printBillingRecoreFile(System.out, s3BillingRecordFile);
});
}
System.out.println();
// Finally, if you want to search the billing files using some other criteria you can pass in a
// predicate. Note
// that this predicate version of scan() isn't magic: you can just pass the same predicate to
// the filter()
// method of the resultant stream.
System.out.println("Printing a few detailed line item files where the month is Jan or Feb...");
Predicate<S3BillingRecordFile> searchPredicate =
billingRecordFile -> billingRecordFile.getMonth() < 3;
try (Stream<S3BillingRecordFile> billingRecordFileStream = fileScanner.scan(searchPredicate)) {
billingRecordFileStream
.limit(5)
.forEach(
s3BillingRecordFile -> {
printBillingRecoreFile(System.out, s3BillingRecordFile);
});
}
System.out.println();
}