我有两个数组映射。
Map<String, List<String>> map1 = new HashMap<>();
Map<String, List<String>> map2 = new HashMap<>();
我希望将它们合并到一个新的映射中。
如果一个键在两个映射中都存在,则应合并数组。
例如:
map1.put("k1", Arrays.asList("a0", "a1"));
map1.put("k2", Arrays.asList("b0", "b1"));
map2.put("k2", Arrays.asList("z1", "z2"));
// Expected output is
Map 3: {k1=[a0, a1], k2=[b0, b1, z1, z2]}
我尝试使用流来完成这个操作
Map<String, List<String>> map3 = Stream.of(map1, map2)
.flatMap(map -> map.entrySet().stream())
.collect(Collectors.toMap(
Map.Entry::getKey,
e -> e.getValue().stream().collect(Collectors.toList())
));
如果在地图中没有相同的键,这将有效。否则,我会得到异常。
Exception in thread "main" java.lang.IllegalStateException: Duplicate key k2 (attempted merging values [b0, b1] and [z1, z2])
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$3ReducingSink.accept(ReduceOps.java:169)
at java.base/java.util.HashMap$EntrySpliterator.forEachRemaining(HashMap.java:1751)
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:658)
at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:274)
at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
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 im.djm.Test.main(Test.java:25)
有没有使用流来完成这个任务的方法?
还是我必须遍历映射?