添加 Java 的 streams 处理模块

2022-05-04 08:27:04 -04:00
parent fa7280f032
commit 18858a282d
23 changed files with 1329 additions and 0 deletions
@@ -0,0 +1,32 @@
+package com.ossez.stream;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.stream.Stream;
+
+public class InfiniteStreams {
+
+    private static final Logger LOG = LoggerFactory.getLogger(InfiniteStreams.class);
+
+    public static void main(String[] args) {
+        doWhileOldWay();
+
+        doWhileStreamWay();
+
+    }
+
+    private static void doWhileOldWay() {
+
+        int i = 0;
+        while (i < 10) {
+            LOG.debug("{}", i);
+            i++;
+        }
+    }
+
+    private static void doWhileStreamWay() {
+        Stream<Integer> integers = Stream.iterate(0, i -> i + 1);
+        integers.limit(10).forEach(System.out::println);
+    }
+}
@@ -0,0 +1,24 @@
+package com.ossez.stream;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+public class StreamApi {
+
+    public static String getLastElementUsingReduce(List<String> valueList) {
+        Stream<String> stream = valueList.stream();
+        return stream.reduce((first, second) -> second).orElse(null);
+    }
+    
+    public static Integer getInfiniteStreamLastElementUsingReduce() {
+        Stream<Integer> stream = Stream.iterate(0, i -> i + 1);
+        return stream.limit(20).reduce((first, second) -> second).orElse(null);
+    }
+    
+    public static String getLastElementUsingSkip(List<String> valueList) {
+        long count = (long) valueList.size();
+        Stream<String> stream = valueList.stream();
+        return stream.skip(count - 1).findFirst().orElse(null);
+    }
+
+}
@@ -0,0 +1,62 @@
+package com.ossez.stream;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import com.codepoetics.protonpack.Indexed;
+import com.codepoetics.protonpack.StreamUtils;
+
+import io.vavr.collection.Stream;
+import one.util.streamex.EntryStream;
+
+public class StreamIndices {
+
+    public static List<String> getEvenIndexedStrings(String[] names) {
+        List<String> evenIndexedNames = IntStream.range(0, names.length)
+            .filter(i -> i % 2 == 0)
+            .mapToObj(i -> names[i])
+            .collect(Collectors.toList());
+        return evenIndexedNames;
+    }
+
+    public List<String> getEvenIndexedStringsVersionTwo(List<String> names) {
+        List<String> evenIndexedNames = EntryStream.of(names)
+            .filterKeyValue((index, name) -> index % 2 == 0)
+            .values()
+            .toList();
+        return evenIndexedNames;
+    }
+
+    public static List<Indexed<String>> getEvenIndexedStrings(List<String> names) {
+        List<Indexed<String>> list = StreamUtils.zipWithIndex(names.stream())
+            .filter(i -> i.getIndex() % 2 == 0)
+            .collect(Collectors.toList());
+        return list;
+    }
+
+    public static List<Indexed<String>> getOddIndexedStrings(List<String> names) {
+        List<Indexed<String>> list = StreamUtils.zipWithIndex(names.stream())
+            .filter(i -> i.getIndex() % 2 == 1)
+            .collect(Collectors.toList());
+        return list;
+    }
+
+    public static List<String> getOddIndexedStrings(String[] names) {
+        List<String> oddIndexedNames = IntStream.range(0, names.length)
+            .filter(i -> i % 2 == 1)
+            .mapToObj(i -> names[i])
+            .collect(Collectors.toList());
+        return oddIndexedNames;
+    }
+
+    public static List<String> getOddIndexedStringsVersionTwo(String[] names) {
+        List<String> oddIndexedNames = Stream.of(names)
+            .zipWithIndex()
+            .filter(tuple -> tuple._2 % 2 == 1)
+            .map(tuple -> tuple._1)
+            .toJavaList();
+        return oddIndexedNames;
+    }
+
+}
@@ -0,0 +1,55 @@
+package com.ossez.stream.filter;
+
+import javax.net.ssl.HttpsURLConnection;
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+public class Customer {
+    private String name;
+    private int points;
+    private String profilePhotoUrl;
+
+    public Customer(String name, int points) {
+        this(name, points, "");
+    }
+
+    public Customer(String name, int points, String profilePhotoUrl) {
+        this.name = name;
+        this.points = points;
+        this.profilePhotoUrl = profilePhotoUrl;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getPoints() {
+        return points;
+    }
+
+    public boolean hasOver(int points) {
+        return this.points > points;
+    }
+
+    public boolean hasOverHundredPoints() {
+        return this.points > 100;
+    }
+
+    public boolean hasValidProfilePhoto() throws IOException {
+        URL url = new URL(this.profilePhotoUrl);
+        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
+        return connection.getResponseCode() == HttpURLConnection.HTTP_OK;
+    }
+
+    public boolean hasValidProfilePhotoWithoutCheckedException() {
+        try {
+            URL url = new URL(this.profilePhotoUrl);
+            HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
+            return connection.getResponseCode() == HttpURLConnection.HTTP_OK;
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}
@@ -0,0 +1,8 @@
+package com.ossez.stream.sum;
+
+public class ArithmeticUtils {
+
+    public static int add(int a, int b) {
+        return a + b;
+    }
+}
@@ -0,0 +1,31 @@
+package com.ossez.stream.sum;
+
+public class Item {
+
+    private int id;
+    private Integer price;
+
+    public Item(int id, Integer price) {
+        super();
+        this.id = id;
+        this.price = price;
+    }
+
+    // Standard getters and setters
+    public long getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public Integer getPrice() {
+        return price;
+    }
+
+    public void setPrice(Integer price) {
+        this.price = price;
+    }
+
+}
@@ -0,0 +1,59 @@
+package com.ossez.stream.sum;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class StreamSumCalculator {
+
+    public static Integer getSumUsingCustomizedAccumulator(List<Integer> integers) {
+        return integers.stream()
+            .reduce(0, ArithmeticUtils::add);
+
+    }
+
+    public static Integer getSumUsingJavaAccumulator(List<Integer> integers) {
+        return integers.stream()
+            .reduce(0, Integer::sum);
+
+    }
+
+    public static Integer getSumUsingReduce(List<Integer> integers) {
+        return integers.stream()
+            .reduce(0, (a, b) -> a + b);
+
+    }
+
+    public static Integer getSumUsingCollect(List<Integer> integers) {
+
+        return integers.stream()
+            .collect(Collectors.summingInt(Integer::intValue));
+
+    }
+
+    public static Integer getSumUsingSum(List<Integer> integers) {
+
+        return integers.stream()
+            .mapToInt(Integer::intValue)
+            .sum();
+    }
+
+    public static Integer getSumOfMapValues(Map<Object, Integer> map) {
+
+        return map.values()
+            .stream()
+            .mapToInt(Integer::valueOf)
+            .sum();
+    }
+
+    public static Integer getSumIntegersFromString(String str) {
+
+        Integer sum = Arrays.stream(str.split(" "))
+            .filter((s) -> s.matches("\\d+"))
+            .mapToInt(Integer::valueOf)
+            .sum();
+
+        return sum;
+    }
+}
@@ -0,0 +1,38 @@
+package com.ossez.stream.sum;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class StreamSumCalculatorWithObject {
+
+    public static Integer getSumUsingCustomizedAccumulator(List<Item> items) {
+        return items.stream()
+            .map(x -> x.getPrice())
+            .reduce(0, ArithmeticUtils::add);
+    }
+
+    public static Integer getSumUsingJavaAccumulator(List<Item> items) {
+        return items.stream()
+            .map(x -> x.getPrice())
+            .reduce(0, Integer::sum);
+    }
+
+    public static Integer getSumUsingReduce(List<Item> items) {
+        return items.stream()
+            .map(item -> item.getPrice())
+            .reduce(0, (a, b) -> a + b);
+    }
+
+    public static Integer getSumUsingCollect(List<Item> items) {
+        return items.stream()
+            .map(x -> x.getPrice())
+            .collect(Collectors.summingInt(Integer::intValue));
+    }
+
+    public static Integer getSumUsingSum(List<Item> items) {
+        return items.stream()
+            .mapToInt(x -> x.getPrice())
+            .sum();
+    }
+
+}
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>