如何在 Java 中测试 JSON 对象是否为空
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How to test if JSON object is empty in Java
提问by Classified
The JSON object I'm receiving looks like this:
我收到的 JSON 对象如下所示：
[{"foo1":"bar1", "foo2":"bar2", "problemkey": "problemvalue"}]
What I'm trying to test for is the existence of problemvalue. If problemvaluereturns a JSON Object, I'm happy. If it doesn't, it will return as {}. How do I test for this condition? I've tried several things to no avail.
我试图测试的是problemvalue. 如果problemvalue返回 JSON 对象，我很高兴。如果没有，它将作为{}. 我如何测试这种情况？我尝试了几件事都无济于事。
This is what I've tried thus far:
这是我迄今为止尝试过的：
// if (obj.get("dps") == null) { //didn't work
// if (obj.get("dps").equals("{}")) { //didn't work
if (obj.isNull("dps")) { //didn't work
System.out.println("No dps key");
}
I expected one of these lines to print "No dps key" because {"dps":{}}, but for whatever reason, it's not. I'm using org.json. The jar file is org.json-20120521.jar.
我希望其中一行打印“No dps key”，因为{"dps":{}}，但无论出于何种原因，事实并非如此。我正在使用org.json. jar 文件是org.json-20120521.jar.
采纳答案by Scott Tesler
obj.length() == 0
is what I would do.
是我会做的。
回答by Orel Eraki
Try:
尝试：
if (record.has("problemkey") && !record.isNull("problemkey")) {
// Do something with object.
}
回答by APerson
Try /*string with {}*/ string.trim().equalsIgnoreCase("{}")), maybe there is some extra spaces or something
试试看/*string with {}*/ string.trim().equalsIgnoreCase("{}"))，也许有一些额外的空格或什么的
回答by Anderson
A JSON notation {} represents an empty object, meaning an object without members. This is not the same as null. Neither it is string as you are trying to compare it with string "{}". I don't know which json library are you using, but try to look for method something like:
JSON 表示法 {} 表示一个空对象，意思是一个没有成员的对象。这与空值不同。当您尝试将它与字符串“{}”进行比较时，它都不是字符串。我不知道您使用的是哪个 json 库，但请尝试查找类似以下内容的方法：
isEmptyObject()
回答by Hot Licks
Object getResult = obj.get("dps");
if (getResult != null && getResult instanceof java.util.Map && (java.util.Map)getResult.isEmpty()) {
handleEmptyDps();
}
else {
handleResult(getResult);
}
回答by djechlin
If you're okay with a hack -
如果你能接受黑客攻击 -
obj.toString().equals("{}");
Serializing the object is expensive and moreso for large objects, but it's good to understand that JSON is transparent as a string, and therefore looking at the string representation is something you can always do to solve a problem.
序列化对象是昂贵的，对于大对象更是如此，但最好理解 JSON 作为字符串是透明的，因此查看字符串表示是您始终可以解决问题的方法。
回答by user3487921
Use the following code:
使用以下代码：
if(json.isNull()!= null){ //returns true only if json is not null
}
回答by kommradHomer
I have added isEmpty() methods on JSONObject and JSONArray()
我在 JSONObject 和 JSONArray() 上添加了 isEmpty() 方法
//on JSONObject
public Boolean isEmpty(){
return !this.keys().hasNext();
}
...
...
//on JSONArray
public Boolean isEmpty(){
return this.length()==0;
}
you can get it here https://github.com/kommradHomer/JSON-java
回答by sorjef
I would do the following to check for an empty object
我会执行以下操作来检查空对象
obj.similar(new JSONObject())
回答by Alex
If JSON returned with following structure when records is an ArrayNode:
如果记录为 ArrayNode 时 JSON 返回具有以下结构：
{}client
records[]
and you want to check if records node has something in it then you can do it using a method size();
并且您想检查记录节点中是否有内容，那么您可以使用方法 size();
if (recordNodes.get(i).size() != 0) {}
