Java 8 - 使用 JsonObject (javax.json) - 如何确定一个节点是否有子节点？
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Java 8 - working with JsonObject (javax.json) - how to determine if a node has child nodes?
提问by Lurker
I've just started using javax.json package. I know how to extract values from JSON object in Java 8 if I know the structure of my JSON string. But how about strings I don't know the structure of? The question: how to determine if a node has child nodes?
我刚刚开始使用 javax.json 包。如果我知道 JSON 字符串的结构，我就知道如何从 Java 8 中的 JSON 对象中提取值。但是我不知道结构的字符串呢？问题：如何判断一个节点是否有子节点？
To read values, I simply need to use "get*" methods - it works OK, but there's no method like "checkIfArray" or "checkIfObject" to check if I even can use methods like "getString"...
要读取值，我只需要使用“get*”方法 - 它工作正常，但没有像“checkIfArray”或“checkIfObject”这样的方法来检查我是否甚至可以使用像“getString”这样的方法......
采纳答案by M. Prokhorov
In javax.jsonpackage, both available types support emptiness checks because they both implement a java.collectioninterfaces:
在javax.json包中，两种可用类型都支持空检查，因为它们都实现了一个java.collection接口：
JsonObjectis-a java.util.Map<String, JsonValue>. As a result, one can check if such object contains any values by simply calling isEmpty()method.
JsonObject是-a java.util.Map<String, JsonValue>。因此，可以通过简单地调用isEmpty()方法来检查此类对象是否包含任何值。
JsonArrayis-a java.util.List<JsonValue>. As a result, one - again - can check if the array is empty by calling isEmpty()method on it.
JsonArray是-a java.util.List<JsonValue>。因此，再次 - 可以通过调用数组的isEmpty()方法来检查数组是否为空。
For traversing a tree of JsonStructures while marking all empty nodes, you can use this helper method:
为了JsonStructure在标记所有空节点的同时遍历s树，您可以使用此辅助方法：
boolean isValueEmpty(JsonValue v) {
if (v == null) {
return true; // or you may throw an exception, for example
}
switch(v.getValueType()) {
case NULL:
return true; // same as with Java null, we assume that it is Empty
case ARRAY:
return ((JsonArray) v).isEmpty();
// additionally, you can say that empty array is array with only empty elements
// this means a check like this:
// return ((JsonArray v).stream().allMatch(isValueEmpty); // recurse
case OBJECT:
return ((JsonObject v).isEmpty();
case STRING:
// optionally: if you want to treat '' as empty
return ((JsonString v).getString().isEmpty();
default:
return false; // to my knowledge, no other Json types can be empty
}
}
