JAVA - Stream - stream has already been operated upon or closed

原因

Stream只能被消费一次，当其调用了终止操作后便说明其已被消费掉了。如果还想重新使用，可考虑在原始数据中重新获得。

错误代码

public void test1(){List<Person> list = new ArrayList();list.add(new Person("妖姬", "女",19));list.add(new Person("张三", "男",19));list.add(new Person("李四", "男",20));list.add(new Person("王五", "男",20));list.add(new Person("赵六", "男",21));list.add(new Person("卡莎", "女",21));Stream<Person> stream = list.stream();List<Person> tempList1 = stream.filter(person -> person.getAge() > 20).collect(Collectors.toList());System.out.println(tempList1);List<Person> tempList2 = stream.filter(person -> "女".equals(person.getGender())).collect(Collectors.toList());System.out.println(tempList2);
}

从日志中可以看出 tempList1是有被打印出来的，错误发生在获取tempList2的过程中。而tempList2获取失败的原因就是在获取tempList1的时候调用了collect的方法，该方法为终止操作，执行完后就代表stream已经被消费了。

修改

public void test1(){List<Person> list = new ArrayList();list.add(new Person("妖姬", "女",19));list.add(new Person("张三", "男",19));list.add(new Person("李四", "男",20));list.add(new Person("王五", "男",20));list.add(new Person("赵六", "男",21));list.add(new Person("卡莎", "女",21));List<Person> tempList1 = list.stream().filter(person -> person.getAge() > 20).collect(Collectors.toList());System.out.println(tempList1);List<Person> tempList2 = list.stream().filter(person ->"女".equals(person.getGender())).collect(Collectors.toList());System.out.println(tempList2);
}

改造后的代码，重新从原始数据中获取流就不会出现异常。

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JAVA - Stream - stream has already been operated upon or closed

原因

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