Java8的stream流中的toMap函数

 @Testpublic void test() {User user = new User();user.setName("123");user.setPassword("123");User user1 = new User();user1.setName("123");user1.setPassword("124");User user2 = new User();user2.setName("124");user2.setPassword("125");User user3 = new User();user3.setName("125");user3.setPassword("125");List<User> users = new ArrayList<>();users.add(user);users.add(user1);users.add(user2);users.add(user3);Map<String, List<User>> userMap = users.stream().collect(Collectors.toMap(User::getName, p -> {List<User> list = new ArrayList<>();list.add(user);return list;}, (List<User> value1, List<User> value2) -> {value1.addAll(value2);return value1;}));System.out.println(userMap.toString());}
}

"C:\Program Files\Java\jdk-11.0.5\bin\java.exe" -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:E:\sofe\Idea\IntelliJ IDEA 2019.2.4\lib\idea_rt.jar=63858:E:\sofe\Idea\IntelliJ IDEA 2019.2.4\bin" -Dfile.encoding=UTF-8 -classpath "E:\sofe\Idea\IntelliJ IDEA 2019.2.4\lib\idea_rt.jar;E:\sofe\Idea\IntelliJ IDEA 2019.2.4\plugins\junit\lib\junit-rt.jar;E:\sofe\Idea\IntelliJ IDEA 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E:\sofe\maven\maven-repository-20191031\org\springframework\spring-context-support\5.2.2.RELEASE\spring-context-support-5.2.2.RELEASE.jar;E:\sofe\maven\maven-repository-20191031\io\lettuce\lettuce-core\5.2.1.RELEASE\lettuce-core-5.2.1.RELEASE.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-common\4.1.43.Final\netty-common-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-handler\4.1.43.Final\netty-handler-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-buffer\4.1.43.Final\netty-buffer-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-codec\4.1.43.Final\netty-codec-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-transport\4.1.43.Final\netty-transport-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\netty\netty-resolver\4.1.43.Final\netty-resolver-4.1.43.Final.jar;E:\sofe\maven\maven-repository-20191031\io\projectreactor\reactor-core\3.3.1.RELEASE\reactor-core-3.3.1.RELEASE.jar;E:\sofe\maven\maven-repository-20191031\org\reactivestreams\reactive-streams\1.0.3\reactive-streams-1.0.3.jar;E:\sofe\maven\maven-repository-20191031\cn\hutool\hutool-all\4.3.1\hutool-all-4.3.1.jar;E:\sofe\maven\maven-repository-20191031\io\jsonwebtoken\jjwt\0.7.0\jjwt-0.7.0.jar;E:\sofe\maven\maven-repository-20191031\com\fasterxml\jackson\core\jackson-databind\2.10.1\jackson-databind-2.10.1.jar;E:\sofe\maven\maven-repository-20191031\com\fasterxml\jackson\core\jackson-annotations\2.10.1\jackson-annotations-2.10.1.jar;E:\sofe\maven\maven-repository-20191031\com\fasterxml\jackson\core\jackson-core\2.10.1\jackson-core-2.10.1.jar;E:\sofe\maven\maven-repository-20191031\org\apache\commons\commons-pool2\2.7.0\commons-pool2-2.7.0.jar;E:\sofe\maven\maven-repository-20191031\javax\xml\bind\jaxb-api\2.3.0\jaxb-api-2.3.0.jar;E:\sofe\maven\maven-repository-20191031\com\sun\xml\bind\jaxb-impl\2.3.0\jaxb-impl-2.3.0.jar;E:\sofe\maven\maven-repository-20191031\com\sun\xml\bind\jaxb-core\2.3.0\jaxb-core-2.3.0.jar;E:\sofe\maven\maven-repository-20191031\javax\activation\activation\1.1.1\activation-1.1.1.jar;E:\sofe\maven\maven-repository-20191031\org\apache\poi\poi-ooxml\4.1.0\poi-ooxml-4.1.0.jar;E:\sofe\maven\maven-repository-20191031\org\apache\poi\poi\4.1.0\poi-4.1.0.jar;E:\sofe\maven\maven-repository-20191031\commons-codec\commons-codec\1.13\commons-codec-1.13.jar;E:\sofe\maven\maven-repository-20191031\org\apache\commons\commons-collections4\4.3\commons-collections4-4.3.jar;E:\sofe\maven\maven-repository-20191031\org\apache\commons\commons-math3\3.6.1\commons-math3-3.6.1.jar;E:\sofe\maven\maven-repository-20191031\org\apache\poi\poi-ooxml-schemas\4.1.0\poi-ooxml-schemas-4.1.0.jar;E:\sofe\maven\maven-repository-20191031\org\apache\xmlbeans\xmlbeans\3.1.0\xmlbeans-3.1.0.jar;E:\sofe\maven\maven-repository-20191031\org\apache\commons\commons-compress\1.18\commons-compress-1.18.jar;E:\sofe\maven\maven-repository-20191031\com\github\virtuald\curvesapi\1.06\curvesapi-1.06.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit5 com.example.demo.mapper.UserMapperTest,test
10:34:11.101 [main] DEBUG org.springframework.test.context.BootstrapUtils - Instantiating CacheAwareContextLoaderDelegate from class [org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate]
10:34:11.116 [main] DEBUG org.springframework.test.context.BootstrapUtils - Instantiating BootstrapContext using constructor [public org.springframework.test.context.support.DefaultBootstrapContext(java.lang.Class,org.springframework.test.context.CacheAwareContextLoaderDelegate)]
10:34:11.148 [main] DEBUG org.springframework.test.context.BootstrapUtils - Instantiating TestContextBootstrapper for test class [com.example.demo.mapper.UserMapperTest] from class [org.springframework.boot.test.context.SpringBootTestContextBootstrapper]
10:34:11.167 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper - Neither @ContextConfiguration nor @ContextHierarchy found for test class [com.example.demo.mapper.UserMapperTest], using SpringBootContextLoader
10:34:11.174 [main] DEBUG org.springframework.test.context.support.AbstractContextLoader - Did not detect default resource location for test class [com.example.demo.mapper.UserMapperTest]: class path resource [com/example/demo/mapper/UserMapperTest-context.xml] does not exist
10:34:11.175 [main] DEBUG org.springframework.test.context.support.AbstractContextLoader - Did not detect default resource location for test class [com.example.demo.mapper.UserMapperTest]: class path resource [com/example/demo/mapper/UserMapperTestContext.groovy] does not exist
10:34:11.175 [main] INFO org.springframework.test.context.support.AbstractContextLoader - Could not detect default resource locations for test class [com.example.demo.mapper.UserMapperTest]: no resource found for suffixes {-context.xml, Context.groovy}.
10:34:11.176 [main] INFO org.springframework.test.context.support.AnnotationConfigContextLoaderUtils - Could not detect default configuration classes for test class [com.example.demo.mapper.UserMapperTest]: UserMapperTest does not declare any static, non-private, non-final, nested classes annotated with @Configuration.
10:34:11.235 [main] DEBUG org.springframework.test.context.support.ActiveProfilesUtils - Could not find an 'annotation declaring class' for annotation type [org.springframework.test.context.ActiveProfiles] and class [com.example.demo.mapper.UserMapperTest]
10:34:11.345 [main] DEBUG org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider - Identified candidate component class: file [E:\demo\target\classes\com\example\demo\SimpleApplication.class]
10:34:11.346 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper - Found @SpringBootConfiguration com.example.demo.SimpleApplication for test class com.example.demo.mapper.UserMapperTest
10:34:11.487 [main] DEBUG org.springframework.boot.test.context.SpringBootTestContextBootstrapper - @TestExecutionListeners is not present for class [com.example.demo.mapper.UserMapperTest]: using defaults.
10:34:11.487 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper - Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener, org.springframework.boot.test.mock.mockito.ResetMocksTestExecutionListener, org.springframework.boot.test.autoconfigure.restdocs.RestDocsTestExecutionListener, org.springframework.boot.test.autoconfigure.web.client.MockRestServiceServerResetTestExecutionListener, org.springframework.boot.test.autoconfigure.web.servlet.MockMvcPrintOnlyOnFailureTestExecutionListener, org.springframework.boot.test.autoconfigure.web.servlet.WebDriverTestExecutionListener, org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener, org.springframework.test.context.event.EventPublishingTestExecutionListener, org.springframework.security.test.context.support.WithSecurityContextTestExecutionListener, org.springframework.security.test.context.support.ReactorContextTestExecutionListener]
10:34:11.512 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper - Using TestExecutionListeners: [org.springframework.test.context.web.ServletTestExecutionListener@5d8bafa9, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@576f63f6, org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener@2dca0d64, org.springframework.boot.test.autoconfigure.SpringBootDependencyInjectionTestExecutionListener@f80945f, org.springframework.test.context.support.DirtiesContextTestExecutionListener@ff684e1, org.springframework.test.context.transaction.TransactionalTestExecutionListener@23aa363a, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@5ef6ae06, org.springframework.test.context.event.EventPublishingTestExecutionListener@55dfebeb, org.springframework.security.test.context.support.WithSecurityContextTestExecutionListener@6e35bc3d, org.springframework.security.test.context.support.ReactorContextTestExecutionListener@1cdc4c27, org.springframework.boot.test.mock.mockito.ResetMocksTestExecutionListener@77b14724, org.springframework.boot.test.autoconfigure.restdocs.RestDocsTestExecutionListener@5d9b7a8a, org.springframework.boot.test.autoconfigure.web.client.MockRestServiceServerResetTestExecutionListener@1e8ce150, org.springframework.boot.test.autoconfigure.web.servlet.MockMvcPrintOnlyOnFailureTestExecutionListener@604f2bd2, org.springframework.boot.test.autoconfigure.web.servlet.WebDriverTestExecutionListener@1d3ac898]
10:34:11.517 [main] DEBUG org.springframework.test.context.support.AbstractDirtiesContextTestExecutionListener - Before test class: context [DefaultTestContext@1ecee32c testClass = UserMapperTest, testInstance = [null], testMethod = [null], testException = [null], mergedContextConfiguration = [WebMergedContextConfiguration@4372b9b6 testClass = UserMapperTest, locations = '{}', classes = '{class com.example.demo.SimpleApplication}', contextInitializerClasses = '[]', activeProfiles = '{}', propertySourceLocations = '{}', propertySourceProperties = '{org.springframework.boot.test.context.SpringBootTestContextBootstrapper=true}', contextCustomizers = set[org.springframework.boot.test.context.filter.ExcludeFilterContextCustomizer@6a8658ff, org.springframework.boot.test.json.DuplicateJsonObjectContextCustomizerFactory$DuplicateJsonObjectContextCustomizer@55de24cc, org.springframework.boot.test.mock.mockito.MockitoContextCustomizer@0, org.springframework.boot.test.web.client.TestRestTemplateContextCustomizer@821330f, org.springframework.boot.test.autoconfigure.properties.PropertyMappingContextCustomizer@0, org.springframework.boot.test.autoconfigure.web.servlet.WebDriverContextCustomizerFactory$Customizer@14dd7b39], resourceBasePath = 'src/main/webapp', contextLoader = 'org.springframework.boot.test.context.SpringBootContextLoader', parent = [null]], attributes = map['org.springframework.test.context.web.ServletTestExecutionListener.activateListener' -> true]], class annotated with @DirtiesContext [false] with mode [null].
10:34:11.560 [main] DEBUG org.springframework.test.context.support.TestPropertySourceUtils - Adding inlined properties to environment: {spring.jmx.enabled=false, org.springframework.boot.test.context.SpringBootTestContextBootstrapper=true, server.port=-1}.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.2.2.RELEASE)2019-12-17 10:34:12.076  INFO 87840 --- [           main] com.example.demo.mapper.UserMapperTest   : Starting UserMapperTest on LAPTOP-5L33IHOU with PID 87840 (started by Lenovo in E:\demo)
2019-12-17 10:34:12.078 DEBUG 87840 --- [           main] com.example.demo.mapper.UserMapperTest   : Running with Spring Boot v2.2.2.RELEASE, Spring v5.2.2.RELEASE
2019-12-17 10:34:12.079  INFO 87840 --- [           main] com.example.demo.mapper.UserMapperTest   : No active profile set, falling back to default profiles: default
2019-12-17 10:34:13.309  INFO 87840 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Multiple Spring Data modules found, entering strict repository configuration mode!
2019-12-17 10:34:13.313  INFO 87840 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data Redis repositories in DEFAULT mode.
2019-12-17 10:34:13.361  INFO 87840 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 23ms. Found 0 Redis repository interfaces.
2019-12-17 10:34:14.041  INFO 87840 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-12-17 10:34:18.143  INFO 87840 --- [           main] o.s.s.web.DefaultSecurityFilterChain     : Creating filter chain: any request, [org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter@40d96578, org.springframework.security.web.context.SecurityContextPersistenceFilter@19f02280, org.springframework.security.web.header.HeaderWriterFilter@28a6e171, org.springframework.web.filter.CorsFilter@c97721b, org.springframework.security.web.authentication.logout.LogoutFilter@5d9618f2, org.springframework.security.web.savedrequest.RequestCacheAwareFilter@cc9ef8d, org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter@fbe70d8, org.springframework.security.web.authentication.AnonymousAuthenticationFilter@283ab206, org.springframework.security.web.session.SessionManagementFilter@265c1a7c, org.springframework.security.web.access.ExceptionTranslationFilter@1472208d, org.springframework.security.web.access.intercept.FilterSecurityInterceptor@359ceb13]
2019-12-17 10:34:18.217 ERROR 87840 --- [           main] o.a.catalina.core.AprLifecycleListener   : An incompatible version [1.2.8] of the APR based Apache Tomcat Native library is installed, while Tomcat requires version [1.2.14]
2019-12-17 10:34:18.527  INFO 87840 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-12-17 10:34:19.467  INFO 87840 --- [           main] com.example.demo.mapper.UserMapperTest   : Started UserMapperTest in 7.894 seconds (JVM running for 9.218){123=[User(id=null, password=123, name=123, createTime=null, updateTime=null, role=null), User(id=null, password=123, name=123, createTime=null, updateTime=null, role=null)], 124=[User(id=null, password=123, name=123, createTime=null, updateTime=null, role=null)], 125=[User(id=null, password=123, name=123, createTime=null, updateTime=null, role=null)]}2019-12-17 10:34:19.990  INFO 87840 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'Process finished with exit code 0

list 转化为map出现key重复：

 @Testpublic void testList() {User user = new User();user.setName("123");user.setPassword("123");User user1 = new User();user1.setName("123");user1.setPassword("124");User user2 = new User();user2.setName("124");user2.setPassword("125");User user3 = new User();user3.setName("125");user3.setPassword("125");List<User> users = new ArrayList<>();users.add(user);users.add(user1);users.add(user2);users.add(user3);Map<String, String> userMap = users.stream().collect(Collectors.toMap(User::getName, User::getPassword));System.out.println(userMap);}

java.lang.IllegalStateException: Duplicate key 123 (attempted merging values 123 and 124)at java.base/java.util.stream.Collectors.duplicateKeyException(Collectors.java:133)at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654)at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)at com.example.demo.mapper.UserMapperTest.testList(UserMapperTest.java:183)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.base/java.lang.reflect.Method.invoke(Method.java:566)at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:675)at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:125)at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:132)at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:124)at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:74)at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:104)at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:62)at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:43)at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:35)at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:202)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:198)at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:69)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128)at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:69)at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

解决：1.将后面的值覆盖前面的值

 Map<String, String> userMap = users.stream().collect(Collectors.toMap(User::getName, User::getPassword, (String name1, String name2) -> name2));System.out.println(userMap);


{123=124, 124=125, 125=125}2019-12-17 15:15:18.432  INFO 98828 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'Process finished with exit code 0

2.将重复值拼接后返回

Map<String, String> userMap = users.stream().collect(Collectors.toMap(User::getName, User::getPassword, (String name1, String name2) -> name1 + ":" + name2));System.out.println(userMap);

{123=123:124, 124=125, 125=125}2019-12-17 15:19:39.014  INFO 94772 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'Process finished with exit code 0

3.将重复的值返回成集合

Map<String, List<String>> userMap = users.stream().collect(Collectors.toMap(User::getName, perUser -> {List<String> list = new ArrayList<>();list.add(perUser.getPassword());return list;},(List<String> password1, List<String> password2) -> {password1.addAll(password2);return password1;}));System.out.println(userMap);


{123=[123, 124], 124=[125], 125=[125]}2019-12-17 15:40:05.683  INFO 101176 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'Process finished with exit code 0

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