Java-8 JSONArray 到 HashMap
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Java-8 JSONArray to HashMap
提问by Pankaj Singhal
I'm trying to convert JSONArrayto a Map<String,String>via streamsand Lambdas. The following isn't working:
我正在尝试转换JSONArray为Map<String,String>viastreams和Lambdas. 以下不起作用：
org.json.simple.JSONArray jsonArray = new org.json.simple.JSONArray();
jsonArray.add("pankaj");
HashMap<String, String> stringMap = jsonArray.stream().collect(HashMap<String, String>::new, (map,membermsisdn) -> map.put((String)membermsisdn,"Error"), HashMap<String, String>::putAll);
HashMap<String, String> stringMap1 = jsonArray.stream().collect(Collectors.toMap(member -> member, member -> "Error"));
To Avoid typecasting in Line 4, I'm doing Line 3
为了避免在 中Line 4进行类型转换，我正在做Line 3
Line 3gives the following errors:
Line 3给出以下错误：
Multiple markers at this line
- The type HashMap<String,String> does not define putAll(Object, Object) that is applicable here
- The method put(String, String) is undefined for the type Object
- The method collect(Supplier, BiConsumer, BiConsumer) in the type Stream is not applicable for the arguments (HashMap<String, String>::new, (<no type> map, <no type> membermsisdn)
-> {}, HashMap<String, String>::putAll)
And Line 4gives the following error:
并Line 4给出以下错误：
Type mismatch: cannot convert from Object to HashMap<String,String>
I'm trying to learn Lambdas and streams. Can somebody help me out?
我正在尝试学习 Lambdas 和流。有人可以帮我吗？
采纳答案by Sam Sun
It would appear that json-simple's JSONArrayextends an ArrayListwithout providing any generic types. This causes streamto return a Streamthat doesn't have a type either.
看起来 json-simple 的JSONArray扩展ArrayList没有提供任何泛型类型。这会导致stream返回一个Stream也没有类型的。
Knowing this, we can program on the interface of Listinstead of JSONArray
知道了这一点，我们可以在接口上编程List而不是JSONArray
List<Object> jsonarray = new JSONArray();
Doing this will allow us to stream properly like so:
这样做将使我们能够像这样正确地流式传输：
Map<String, String> map = jsonarray.stream().map(Object::toString).collect(Collectors.toMap(s -> s, s -> "value"));
