解决lambda集合转map，key重复导致异常问题

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例：

public static void main(String[] args) {
    List<AreaEntity> list = new ArrayList<>();
    AreaEntity entity = null;

    for (int i = 1; i < 10; i++) {
        entity = new AreaEntity();

        entity.setId(i);
        if (i > 6) {
            entity.setName("TEST-T");
        } else {
            entity.setName("TEST-" + i);
        }

        list.add(entity);
    }

    Map<String, Integer> map = list.stream().collect(Collectors.toMap(AreaEntity::getName, AreaEntity::getId));

    map.entrySet().stream().forEach(e -> System.out.println(e.getValue()));
}      

报错：

java.lang.IllegalStateException: Duplicate key 7

问题分析

从异常可以看出，是在调用Collectors.toMap时出错，查看toMap的API：https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html#toMap-java.util.function.Function-java.util.function.Function-

// 方式一
Map<String, Integer> map = list.stream().collect(Collectors.toMap(AreaEntity::getName, AreaEntity::getId, (value1, value2) -> {
    return value2;
}));

// 方式二
Map<String, Integer> map = list.stream().collect(Collectors.toMap(AreaEntity::getName, AreaEntity::getId, (value1, value2) -> value2));