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واجهات برمجة التطبيقات التي تستحق الترقية إليها من جافا 8. الجزء 2

نواصل قصة APIs التي ظهرت في إصدارات جديدة من Java.



1. Files.mismatch()


ظهرت في: Java 12


من الناحية العملية ، غالبًا ما يكون من الضروري التحقق مما إذا كان الملفان متماثلان تمامًا أم لا. باستخدام الطريقة Files.mismatch()المقدمة في Java 12 ، يمكن القيام بذلك أخيرًا. تقوم هذه الطريقة بإرجاع موضع أول بايت عدم تطابق في ملفين ، أو -1إذا كانت الملفات متطابقة.


يمكن أن يكون ذلك مفيدًا ، على سبيل المثال ، عندما تقوم بمزامنة محتويات دليلين. لكي لا تستبدل الملف عند النسخ بنفس المحتويات ولا تقوم بتحميل القرص مرة أخرى ، يمكنك أولاً التحقق مما إذا كانت الملفات متطابقة أم لا:


public static void syncDirs(Path srcDir, Path dstDir)
        throws IOException {
    //    ,   
    try (Stream<Path> stream = Files.list(srcDir)) {
        for (Path src : stream.collect(toList())) {
            Path dst = dstDir.resolve(src.getFileName());
            if (!Files.exists(dst)) {
                System.out.println("Copying file " + dst);
                Files.copy(src, dst);
            } else if (Files.mismatch(src, dst) >= 0) {
                System.out.println("Overwriting file " + dst);
                Files.copy(src, dst, StandardCopyOption.REPLACE_EXISTING);
            }
        }
    }
}

(بالمناسبة ، متى Streamيرثون في النهاية Iterable؟ أريد فقط الكتابة for (Path file : stream)، وعدم العبث بالقوائم الوسيطة.)


2. طرق جديدة في java.time


المقدمة في: Java 9


لما يقرب من 20 عامًا ، لم يكن لدى Java واجهة برمجة تطبيقات عادية للعمل مع التواريخ والأوقات. تم حل هذه المشكلة فقط في Java 8 عندما قدموا حزمة جديدة java.timeتحت إشراف ستيفن كولبورن سيئ السمعة ، مبتكر مكتبة جودا تايم . وفي الإصدار التاسع java.time، تمت إضافة العديد من الطرق المثيرة للاهتمام.


Java 8 Duration (, 2 , 7 , 15 , 12 ). Java 9 toDaysPart(), toHoursPart(), toMinutesPart(), toSecondsPart() .. :


public static String modifiedAgo(Path path) throws IOException {
    FileTime time = Files.getLastModifiedTime(path);
    Instant to = Instant.now();
    Instant from = time.toInstant();
    Duration d = Duration.between(from, to);
    return String.format(
        "   %d , %d , %d , %d  ",
        d.toDaysPart(), d.toHoursPart(),
        d.toMinutesPart(), d.toSecondsPart());
}

, ? Java 8, , . Java 9 Duration.dividedBy():


public static long modifiedAgo(Path path, ChronoUnit unit)
        throws IOException {
    FileTime time = Files.getLastModifiedTime(path);
    Instant to = Instant.now();
    Instant from = time.toInstant();
    Duration d = Duration.between(from, to);
    return d.dividedBy(unit.getDuration());
}

public static void main(String[] args) throws Exception {
    Path path = ...
    System.out.printf("   %d  %n",
        modifiedAgo(path, ChronoUnit.MONTHS));
}

LocalDate. LocalDate.ofInstant() Instant LocalDate:


LocalDate date = LocalDate.ofInstant(
    Instant.now(), ZoneId.systemDefault());
System.out.println(date);

LocalDate.datesUntil(), - Stream :


LocalDate from = LocalDate.of(2020, 1, 1);
LocalDate to = LocalDate.of(2020, 1, 9);
from.datesUntil(to)
    .forEach(System.out::println);

:


2020-01-01
2020-01-02
2020-01-03
2020-01-04
2020-01-05
2020-01-06
2020-01-07
2020-01-08

, :


LocalDate from = LocalDate.of(2020, 1, 1);
LocalDate to = LocalDate.of(2020, 1, 31);
from.datesUntil(to, Period.ofWeeks(1))
    .forEach(System.out::println);

:


2020-01-01
2020-01-08
2020-01-15
2020-01-22
2020-01-29

:



3. Collection.toArray() -


: Java 11


Java . Collection Java 1.2 :



, ( String[]), :


  • collection.toArray(new String[0]). , , , .
  • collection.toArray(new String[collection.size()]). , , . .

, , IntelliJ IDEA , , .


2016 , , -: - ( JDK 6+). , IDEA , : (default), Java.


, «». Stream.toArray(IntFunction[]) collection.stream().toArray(String[]::new). ? , .


Oracle : , ? Java 11 Collection.toArray(IntFunction[]), .


. , 4 , , :


List<Integer> list = ...;
Integer[] array = list.toArray(Integer[]::new);

4. InputStream: readNBytes(), readAllBytes(), transferTo()


: Java 9 / Java 11


, Java – InputStream. , Java 8 : , , , , , .. , .


Java 9 InputStream.readAllBytes(), . , stdout/stderr :


Process proc = Runtime.getRuntime().exec("java -version");
try (InputStream inputStream = proc.getErrorStream()) {
    byte[] bytes = inputStream.readAllBytes();
    System.out.print(new String(bytes));
}

:


openjdk version "14-ea" 2020-03-17
OpenJDK Runtime Environment (build 14-ea+33-1439)
OpenJDK 64-Bit Server VM (build 14-ea+33-1439, mixed mode, sharing)

N , Java 11 InputStream.readNBytes().


( ) InputStream OutputStream, InputStream.transferTo(). , Java :


Process proc = Runtime.getRuntime().exec("java -version");
Path path = Path.of("out.txt");
try (InputStream inputStream = proc.getErrorStream();
     OutputStream outputStream = Files.newOutputStream(path)) {
    inputStream.transferTo(outputStream);
}

, Reader Writer : Reader.transferTo(), Java 10.


5. Collectors.teeing()


: Java 12


Stream . , Stream Employee, :


  • Stream.
  • , .

Java 8? , : Stream.count(), Stream.filter() Stream.count(). , Stream .


– Stream.forEach():


Stream<Employee> employees = ...
int[] countWithPhoneAndTotal = {0, 0};
employees
    .forEach(emp -> {
        if (emp.getPhoneNumber() != null) {
            countWithPhoneAndTotal[0]++;
        }
        countWithPhoneAndTotal[1]++;
    });
System.out.println("Employees with phone number: "
    + countWithPhoneAndTotal[0]);
System.out.println("Total employees: "
    + countWithPhoneAndTotal[1]);

, , , . Stream.peek() .


Stream.reduce():


class CountWithPhoneAndTotal {
    final int withPhone;
    final int total;

    CountWithPhoneAndTotal(int withPhone, int total) {
        this.withPhone = withPhone;
        this.total = total;
    }
}

CountWithPhoneAndTotal countWithPhoneAndTotal = employees
    .reduce(
        new CountWithPhoneAndTotal(0, 0),
        (count, employee) -> new CountWithPhoneAndTotal(
            employee.getPhoneNumber() != null
                ? count.withPhone + 1
                : count.withPhone,
            count.total + 1),
        (count1, count2) -> new CountWithPhoneAndTotal(
            count1.withPhone + count2.withPhone,
            count1.total + count2.total));
System.out.println("Employees with phone number: "
    + countWithPhoneAndTotal.withPhone);
System.out.println("Total employees: "
    + countWithPhoneAndTotal.total);

, , . -, , -, , CountWithPhoneAndTotal. - , CountWithPhoneAndTotal inline, .


. - , Java 8 , . , Java 12 Collectors.teeing():


Entry<Long, Long> countWithPhoneAndTotal = employees
    .collect(teeing(
        filtering(employee -> employee.getPhoneNumber() != null, counting()),
        counting(),
        Map::entry
    ));

.


Collectors.teeing() : , - . : toBoth, collectingToBoth, collectingToBothAndThen, pairing, bifurcate, distributing, unzipping, forking,… teeing tee, T, . : .


6. Runtime.version()


: Java 9


Java . , ? , . , java.version. java.specification.version… , :


for (String key : Arrays.asList(
        "java.version",
        "java.runtime.version",
        "java.specification.version",
        "java.vm.version",
        "java.vm.specification.version")) {
    System.out.println(key + " = " + System.getProperty(key));
}

Java 8, :


java.version = 1.8.0_192
java.runtime.version = 1.8.0_192-b12
java.specification.version = 1.8
java.vm.version = 25.192-b12
java.vm.specification.version = 1.8

8? , java.specification.version, 1., … , Java 9 :


java.version = 9.0.1
java.runtime.version = 9.0.1+11
java.specification.version = 9
java.vm.version = 9.0.1+11
java.vm.specification.version = 9

, Java 9 API Java 10. API «» , Runtime.version(). Runtime.Version, :


Runtime.Version version = Runtime.version();
System.out.println("Feature = " + version.feature());
System.out.println("Interim = " + version.interim());
System.out.println("Update = " + version.update());
System.out.println("Patch = " + version.patch());

, , JDK 11.0.5:


Feature = 11
Interim = 0
Update = 5
Patch = 0

7. Optional.isEmpty()


: Java 11


, , :


if (!stream.findAny().isPresent()) {
    System.out.println("Stream is empty");
}

Optional.isEmpty(), :


if (stream.findAny().isEmpty()) {
    System.out.println("Stream is empty");
}

:


Stream<Optional<Integer>> stream = Stream.of(
    Optional.of(1),
    Optional.empty(),
    Optional.of(2));

long emptyCount = stream
    .filter(Optional::isEmpty) //  opt -> !opt.isPresent()
    .count();

8. HTTP-


: Java 11


API HTTP HttpURLConnection, Java . , : , HTTP/2 -, , . HTTP Client, Java 9 , Java 11.


java.net.http, HttpClient. , HTTP- :


HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest
    .newBuilder(new URI("https://minijug.ru"))
    .build();

HttpResponse<Stream<String>> response = client.send(request,
    HttpResponse.BodyHandlers.ofLines());

System.out.println("Status code = " + response.statusCode());
System.out.println("Body = ");
//  4 
response.body().limit(4).forEach(System.out::println);

:


Status code = 200
Body =
<!doctype html>
<html>
  <head>
    <title>miniJUG</title>

java.net.http , , .


9. Lookup.defineClass()


: Java 9


? , , Java 8 . Unsafe.defineClass() Unsafe.defineAnonymousClass(), API, .


: , , MethodHandles.Lookup.defineClass(), Java 9. :


// Main.java
import java.lang.invoke.MethodHandles;
import java.nio.file.Files;
import java.nio.file.Path;

public class Main {
    public static void main(String[] args) throws Exception {
        byte[] bytes = Files.readAllBytes(Path.of("Temp.class"));
        Class<?> clazz = MethodHandles.lookup().defineClass(bytes);
        Object obj = clazz.getDeclaredConstructor().newInstance();
        System.out.println(obj);
    }
}

// Temp.java
class Temp {
    @Override
    public String toString() {
        return "Hello from Temp!";
    }
}

Temp, Main


> javac Temp.java

> javac Main.java

> java Main
Hello from Temp!

, , Temp Main ( , ). Temp , - , Temp, .


, , . defineClass() , , . , . ToolProvider.getSystemJavaCompiler(), java.compiler ( ).


10. ByteArrayOutputStream.writeBytes()


: Java 11


ByteArrayOutputStream.writeBytes() – ByteArrayOutputStream.write() : write() throws IOException, writeBytes() – (IOException write(), OutputStream). , Java 11, ByteArrayOutputStream :


private static byte[] concat(Stream<byte[]> stream) {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    // stream.forEach(out::write); ( )
    stream.forEach(out::writeBytes);
    return out.toByteArray();
}

: IndexOutOfBoundsException(int)


: Java 9


Java 9: IndexOutOfBoundsException , , :


private static void doAtIndex(int index) {
    if (index < 0) {
        throw new IndexOutOfBoundsException(index);
    }
    // ...
}

public static void main(String[] args) {
    // java.lang.IndexOutOfBoundsException: Index out of range: -1
    doAtIndex(-1);
}


, 10 (+1) API, Java. ? , .

Source: https://habr.com/ru/post/undefined/

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