list转map
java8 lambda将List转换为Map比较简单，但是 有坑：
List<Boy> sellOutList = Lists.newArrayList();
Boy one = new Boy();
one.setId(34343);
sellOutList.add(one);
Boy two = new Boy();
two.setId(34343);
sellOutList.add(two);
Map<Integer, Boy> res = sellOutList.stream().collect(Collectors.toMap(Boy::getId, Function.identity()));
System.out.println(res.entrySet());
public static class Boy{
int id;
int age;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
注意这里使用的是：Function.identity()；
这里运行会报错，报错信息：
java.lang.IllegalStateException: Duplicate key com.serviceTest.ServiceTest$Boy@6c6017b9
at java.util.stream.Collectors.lambda$throwingMerger$106(Collectors.java:133)
at java.util.stream.Collectors$$Lambda$4/38625764.apply(Unknown Source)
at java.util.HashMap.merge(HashMap.java:1245)
at java.util.stream.Collectors.lambda$toMap$164(Collectors.java:1320)
at java.util.stream.Collectors$$Lambda$6/940448009.accept(Unknown Source)
at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:80)
at org.testng.internal.MethodInvocationHelper$1.runTestMethod(MethodInvocationHelper.java:182)
at org.springframework.test.context.testng.AbstractTestNGSpringContextTests.run(AbstractTestNGSpringContextTests.java:171)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.testng.internal.MethodInvocationHelper.invokeHookable(MethodInvocationHelper.java:194)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:707)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
at org.testng.TestRunner.privateRun(TestRunner.java:767)
at org.testng.TestRunner.run(TestRunner.java:617)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
at org.testng.SuiteRunner.run(SuiteRunner.java:240)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1198)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1123)
at org.testng.TestNG.run(TestNG.java:1031)
at org.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:72)
at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:123)
Function.identity() 换成 c->c,(k1, k2)->k2)
正确的写法：
List<Boy> sellOutList = Lists.newArrayList();
Boy one = new Boy();
one.setId(34343);
sellOutList.add(one);
Boy two = new Boy();
two.setId(34343);
sellOutList.add(two);
Map<Integer, Boy> res = sellOutList.stream().collect(Collectors.toMap(Boy::getId, c->c,(k1, k2)->k2));
System.out.println(res.entrySet());
这样就不会报错了。
