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‎README.md

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# java8-lambda-sample
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# java8 sample
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java 8 lambda with actual usage scenarios
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‎pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>wang.crick.study</groupId>
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<artifactId>java8-lambda-sample</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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<name>java8sample</name>
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<url>https://github.com/wangyuheng/java8-lambda-sample</url>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<maven.compiler.source>1.8</maven.compiler.source>
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<maven.compiler.target>1.8</maven.compiler.target>
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</properties>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.11</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<version>1.18.0</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.springframework</groupId>
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<artifactId>spring-core</artifactId>
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<version>5.0.10.RELEASE</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<configuration>
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<source>8</source>
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<target>8</target>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

‎src/main/java/wang/crick/study/java8lambdasample/App.java

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package wang.crick.study.java8lambdasample;
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/**
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* Hello world!
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*
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*/
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public class App
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{
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public static void main( String[] args )
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{
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System.out.println( "Hello World!" );
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}
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}

‎src/test/java/wang/crick/study/java8lambdasample/A1_Optional.java

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package wang.crick.study.java8lambdasample;
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import org.junit.Before;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.Optional;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertFalse;
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/**
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* parse return
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* 1. default?
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* 2. illegalException?
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* 3. null?
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*
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* @author wangyuheng
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* @date 2018-12-17 21:59
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*/
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public class A1_Optional {
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enum BooleanEnum {
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// 封装boolean
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TRUE(1, "是"),
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FALSE(0, "否");
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private Integer key;
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private String label;
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BooleanEnum(Integer key, String label) {
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this.key = key;
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this.label = label;
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}
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public Integer getKey() {
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return key;
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}
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public String getLabel() {
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return label;
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}
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public static Optional<BooleanEnum> parse(Integer key) {
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return Arrays.stream(values()).filter(i -> i.getKey().equals(key)).findAny();
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}
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public static BooleanEnum parse(boolean bool) {
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return bool ? TRUE : FALSE;
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}
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public static boolean exist(int key) {
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return Arrays.stream(values()).anyMatch(i -> i.getKey() == key);
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}
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}
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@Before
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public void setUp() {
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System.out.println("--------------------");
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}
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@Test
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public void parse_true_optional() {
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Optional<BooleanEnum> optionalBooleanEnum = BooleanEnum.parse(1);
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assertEquals(BooleanEnum.TRUE, optionalBooleanEnum.get());
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BooleanEnum.parse(1).ifPresent(System.out::println);
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}
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@Test
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public void parse_false_optional() {
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Optional<BooleanEnum> optionalBooleanEnum = BooleanEnum.parse(0);
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assertEquals(BooleanEnum.FALSE, optionalBooleanEnum.get());
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BooleanEnum.parse(0).ifPresent(System.out::println);
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}
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@Test
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public void parse_empty_optional() {
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Optional<BooleanEnum> optionalBooleanEnum = BooleanEnum.parse(2);
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assertFalse(optionalBooleanEnum.isPresent());
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BooleanEnum.parse(2).ifPresent(System.out::println);
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}
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}

‎src/test/java/wang/crick/study/java8lambdasample/A2_OptionalMap.java

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package wang.crick.study.java8lambdasample;
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import lombok.AllArgsConstructor;
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import lombok.Builder;
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import lombok.Data;
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import lombok.NoArgsConstructor;
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import org.junit.Before;
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import org.junit.Test;
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import java.util.Objects;
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import java.util.Optional;
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import static org.junit.Assert.assertFalse;
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import static org.junit.Assert.assertTrue;
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/**
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* optional if nested
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*
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* @author wangyuheng
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* @date 2018-12-17 21:59
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*/
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public class A2_OptionalMap {
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private String username = "zhangsan";
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private String password = "123456";
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private UserPO userPO;
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@Before
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public void setUp() {
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username = "zhangsan";
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password = "123456";
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userPO = UserPO.builder()
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.username(username)
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.password(password)
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.build();
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System.out.println("--------------------");
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}
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@Test
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public void login_fail_when_incorrect_password() {
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password = "1";
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assertFalse(login_check_by_if(username, password).isPresent());
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assertFalse(login_check_by_map(username, password).isPresent());
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System.out.println(login_check_by_if(username, password));
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System.out.println(login_check_by_map(username, password));
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}
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@Test
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public void login_success_when_incorrect_password() {
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assertTrue(login_check_by_if(username, password).isPresent());
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assertTrue(login_check_by_map(username, password).isPresent());
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System.out.println(login_check_by_if(username, password));
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System.out.println(login_check_by_map(username, password));
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}
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private Optional<User> login_check_by_if(String username, String password) {
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Optional<UserPO> optionalUserPO = findByUsername(username);
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if (optionalUserPO.isPresent()) {
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UserPO po = optionalUserPO.get();
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if (password.equals(po.getPassword())) {
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return Optional.of(convert(po));
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} else {
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return Optional.empty();
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}
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} else {
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return Optional.empty();
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}
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}
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private Optional<User> login_check_by_map(String username, String password) {
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return findByUsername(username)
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.filter(po -> Objects.equals(po.getPassword(), password))
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.map(this::convert);
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}
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private Optional<UserPO> findByUsername(String username) {
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return Optional.ofNullable(userPO);
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}
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private User convert(UserPO po) {
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return User.builder()
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.username(po.getUsername())
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.password(po.getPassword())
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.build();
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}
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@Data
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@Builder
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@AllArgsConstructor
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@NoArgsConstructor
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private static class UserPO {
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private String username;
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private String password;
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}
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@Data
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@Builder
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@AllArgsConstructor
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@NoArgsConstructor
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private static class User {
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private String username;
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private String password;
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}
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}

‎src/test/java/wang/crick/study/java8lambdasample/A3_OptionalStrongGetParam.java

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package wang.crick.study.java8lambdasample;
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import lombok.Data;
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import org.junit.Before;
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import org.junit.Rule;
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import org.junit.Test;
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import org.junit.rules.ExpectedException;
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import java.util.Optional;
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import static org.junit.Assert.*;
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/**
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* get().get().get()
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*
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* @author wangyuheng
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* @date 2018-12-17 21:59
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*/
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public class A3_OptionalStrongGetParam {
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@Rule
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public ExpectedException thrown = ExpectedException.none();
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@Before
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public void setUp() {
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System.out.println("--------------------");
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}
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@Test
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public void get_treasure_npe_when_session_null() {
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Exchange exchange = new Exchange();
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thrown.expect(NullPointerException.class);
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exchange.getSession().getRequest().getTreasure();
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}
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@Test
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public void get_null_treasure() {
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Exchange exchange = new Exchange();
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String result1 = getTreasureIf(exchange);
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Optional<String> result2 = getTreasureOptionalMap(exchange);
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assertNull(result1);
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assertFalse(result2.isPresent());
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}
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@Test
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public void get_treasure() {
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String treasure = "treasure";
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Request request = new Request();
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Session session = new Session();
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Exchange exchange = new Exchange();
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request.setTreasure(treasure);
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session.setRequest(request);
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exchange.setSession(session);
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String result1 = getTreasureIf(exchange);
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Optional<String> result2 = getTreasureOptionalMap(exchange);
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assertEquals(treasure, result1);
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assertEquals(treasure, result2.get());
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}
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private String getTreasureIf(Exchange exchange) {
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if (null != exchange) {
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Session session = exchange.getSession();
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if (null != session) {
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Request request = session.getRequest();
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if (null != request) {
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return request.getTreasure();
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} else {
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return null;
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}
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} else {
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return null;
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}
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} else {
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return null;
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}
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}
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private Optional<String> getTreasureOptionalMap(Exchange exchange) {
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return Optional.ofNullable(exchange)
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.map(Exchange::getSession)
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.map(Session::getRequest)
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.map(Request::getTreasure);
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}
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@Data
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private static class Exchange {
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private Session session;
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}
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@Data
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private static class Session {
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private Request request;
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}
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@Data
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private static class Request {
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private String treasure;
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}
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}

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