blocks|key|3010884|text|JSONObject类有一个名为“has”的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3010885|http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)|offset|length|3010886|如果此对象具有名称的映射，则|3010887|返回true。映射可能为NULL。|blockquote|3010888|3010889|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|2D|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|Y|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|C]]]]

JSONObject class has a method named "has":

<a href="http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)">http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)</a>

<blockquote>
 Returns true if this object has a mapping for name. The mapping may be NULL.
</blockquote>

blocks|key|2798499|text|你可以通过这种方式检查'+has‘-如果这个对象有一个name的映射，返回true。映射可能为空。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2798500|if+(json.has("status"))+{
+++String+status+=+json.getString("status"));
}

if+(json.has("club"))+{
+++String+club+=+json.getString("club"));
}|code-block|syntax|javascript|2798501|如果这个对象没有|2798502|的映射，或者它有一个值为空的映射，你也可以使用'isNull‘来检查，返回true。|blockquote|2798503|2798504|2798505|if+(!json.isNull("club"))
++++String+club+=+json.getString("club"));|2798506|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|U|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|V|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|N|3|O|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|P|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|Q|$]]

You can check this way where 'HAS' - Returns true if this object has a mapping for name. The mapping may be NULL.

<pre><code>if (json.has("status")) {
 String status = json.getString("status"));
}

if (json.has("club")) {
 String club = json.getString("club"));
}
</code></pre>

<blockquote>
 You can also check using 'isNull' - Returns true if this object has no
 mapping for name or if it has a mapping whose value is NULL.
</blockquote>

<pre><code>if (!json.isNull("club"))
 String club = json.getString("club"));
</code></pre>

blocks|key|183356|text|您可以使用JSONObject#has，提供key作为输入并检查该方法返回的是true还是false。你也可以|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|183357|使用optString而不是getString|183358|183359|返回按名称映射的值(如果存在)，并在必要时强制执行该值。如果不存在此类映射，则返回空字符串|blockquote|183360|183361|entityMap^0|5|E|M|3|13|4|19|5|0|2|9|E|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|12|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|13|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|N|$]]

you could <code>JSONObject#has</code>, providing the <code>key</code> as input and check if the method returns <code>true</code> or <code>false</code>. You could also

use <code>optString</code> instead of <code>getString</code>:

<blockquote>
 Returns the value mapped by name if it exists, coercing it if
 necessary. Returns the empty string if no such mapping exists
</blockquote>

blocks|key|186214|text|就在读取密钥之前检查它，就像读取之前一样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|186215|JSONObject+json_obj=new+JSONObject(yourjsonstr);
if(!json_obj.isNull("club"))
{
++//it's+contain+value+to+be+read+operation
}
else
{
++//it's+not+contain+key+club+or+isnull+so+do+this+operation+here
}|code-block|syntax|javascript|186216|isNull函数定义|186217|Returns+true+if+this+object+has+no+mapping+for+name+or
if+it+has+a+mapping+whose+value+is+NULL.+|186218|以下是isNull函数的官方文档链接|offset|length|style|CODE|186219|http://developer.android.com/reference/org/json/JSONObject.html#isNull(java.lang.String)|186220|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|0|3|6|0|0|2G|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|11|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|13|8|@$M|14|N|15|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|16|8|@]|9|@$M|17|N|18|1|19]]|A|$]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|R]]]]

just before read key check it like before read

<pre><code>JSONObject json_obj=new JSONObject(yourjsonstr);
if(!json_obj.isNull("club"))
{
 //it's contain value to be read operation
}
else
{
 //it's not contain key club or isnull so do this operation here
}
</code></pre>

isNull function definition 

<pre><code>Returns true if this object has no mapping for name or
if it has a mapping whose value is NULL. 
</code></pre>

official documentation below link for <code>isNull</code> function

<a href="http://developer.android.com/reference/org/json/JSONObject.html#isNull(java.lang.String)" rel="noreferrer">http://developer.android.com/reference/org/json/JSONObject.html#isNull(java.lang.String)</a>

blocks|key|183389|text|您可以使用has|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|183390|public+boolean+has(String+key)|code-block|syntax|javascript|183391|确定是否包含特定于的密钥。|BOLD|183392|示例|183393|JSONObject+JsonObj+=+new+JSONObject(Your_API_STRING);+//JSONObject+is+an+unordered+collection+of+name/value+pairs

if+(JsonObj.has("address"))+{+
++++//Checking+address+Key+Present+or+not
++++String+get_address+=+JsonObj+.getString("address");+//+Present+Key
}
else+{
++++//Do+Your+Staff
}|183394|entityMap^0|5|3|0|0|9|3|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|W|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|X|8|@$9|Y|A|Z|B|M]]|D|@]|E|$]]|$1|N|3|O|5|6|7|10|8|@$9|11|A|12|B|M]]|D|@]|E|$]]|$1|P|3|Q|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|R|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|S|$]]

You can use <code>has</code>

<pre><code>public boolean has(String key)
</code></pre>

Determine if the <a href="https://developer.android.com/reference/org/json/JSONObject.html" rel="noreferrer">JSONObject</a> contains a specific key.

Example

<pre><code>JSONObject JsonObj = new JSONObject(Your_API_STRING); //JSONObject is an unordered collection of name/value pairs

if (JsonObj.has("address")) { 
 //Checking address Key Present or not
 String get_address = JsonObj .getString("address"); // Present Key
}
else {
 //Do Your Staff
}
</code></pre>

blocks|key|184231|text|一种更好的方法，而不是使用条件，如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|184232|if+(json.has("club"))+{
++++String+club+=+json.getString("club"));
+}|code-block|syntax|javascript|184233|就是简单地使用现有方法optString()，如下所示：|184234|String+club+=+json.optString("club);|184235|如果键不存在，optString("+key+")方法将返回一个空字符串，因此不会抛出异常。|184236|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

A better way, instead of using a conditional like:

<pre><code>if (json.has("club")) {
 String club = json.getString("club"));
 }
</code></pre>

is to simply use the existing method optString(), like this:

<pre><code>String club = json.optString("club);
</code></pre>

the optString("key") method will return an empty String if the key does not exist and won't, therefore, throw you an exception.

blocks|key|183508|text|Json有一个名为containsKey()的方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|183509|您可以使用它来检查Json集合中是否包含某个键。|183510|File+jsonInputFile+=+new+File("jsonFile.json");+
InputStream+is+=+new+FileInputStream(jsonInputFile);
JsonReader+reader+=+Json.createReader(is);
JsonObject+frameObj+=+reader.readObject();
reader.close();

if+frameObj.containsKey("person")+{
++++++//Do+stuff
}|code-block|syntax|javascript|183511|entityMap^0|9|D|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Json has a method called <code>containsKey()</code>. 

You can use it to check if a certain key is contained in the Json set. 

<pre class="lang-java prettyprint-override"><code>File jsonInputFile = new File("jsonFile.json"); 
InputStream is = new FileInputStream(jsonInputFile);
JsonReader reader = Json.createReader(is);
JsonObject frameObj = reader.readObject();
reader.close();

if frameObj.containsKey("person") {
 //Do stuff
}
</code></pre>

blocks|key|3011076|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3011077|let+json=yourJson

if(json.hasOwnProperty(yourKey)){
++++value=json[yourKey]
}|code-block|syntax|javascript|3011078|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try this:

<pre><code>let json=yourJson

if(json.hasOwnProperty(yourKey)){
 value=json[yourKey]
}
</code></pre>

blocks|key|2798508|text|尝尝这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2798509|if(!jsonObj.isNull("club")){
++++jsonObj.getString("club");
}|code-block|syntax|javascript|2798510|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try this

<pre><code>if(!jsonObj.isNull("club")){
 jsonObj.getString("club");
}
</code></pre>

blocks|key|181953|text|I+used+hasOwnProperty('club')

var+myobj+=+{+"regatta_name":"ProbaRegatta",
++++"country":"Congo",
++++"status":"invited"
+};

+if+(+myobj.hasOwnProperty("club"))
+++++//+do+something+with+club+(will+be+false+with+above+data)
+++++var+data+=+myobj.club;
+if+(+myobj.hasOwnProperty("status"))
+++++//+do+something+with+the+status+field.+(will+be+true+with+above+..)
+++++var+data+=+myobj.status;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|181954|适用于所有当前浏览器。|unstyled|181955|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>I used hasOwnProperty('club')

var myobj = { "regatta_name":"ProbaRegatta",
 "country":"Congo",
 "status":"invited"
 };

 if ( myobj.hasOwnProperty("club"))
 // do something with club (will be false with above data)
 var data = myobj.club;
 if ( myobj.hasOwnProperty("status"))
 // do something with the status field. (will be true with above ..)
 var data = myobj.status;
</code></pre>

works in all current browsers.

blocks|key|184274|text|您可以尝试执行此操作来检查密钥是否存在：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|184275|JSONObject+object+=+new+JSONObject(jsonfile);
if+(object.containskey("key"))+{
++object.get("key");
++//etc.+etc.
}|code-block|syntax|javascript|184276|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can try this to check wether the key exists or not:

<pre><code>JSONObject object = new JSONObject(jsonfile);
if (object.containskey("key")) {
 object.get("key");
 //etc. etc.
}
</code></pre>

blocks|key|184266|text|我只是补充一件事，如果你只是想检查是否在JSONObject中创建了任何东西，你可以使用length()，因为在默认情况下，当JSONObject初始化时，没有插入键，它只有空花括号{}，使用有(字符串键)没有任何意义。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|184267|因此，您可以直接编写if+(jsonObject.length()+>+0)并执行您的操作。|184268|祝您学习愉快！|184269|entityMap^0|18|6|2O|1|2J|2|0|A|S|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|T|8|@$9|U|A|V|B|D]]|E|@]|F|$]]|$1|I|3|J|5|6|7|W|8|@]|E|@]|F|$]]|$1|K|3|-4|5|6|7|X|8|@]|E|@]|F|$]]]|L|$]]

I am just adding another thing, In case you just want to check whether anything is created in JSONObject or not you can use length(), because by default when JSONObject is initialized and no key is inserted, it just has empty braces <code>{}</code> and using has(String key) doesn't make any sense.

So you can directly write <code>if (jsonObject.length() &gt; 0)</code> and do your things.

Happy learning!

blocks|key|182101|text|您可以使用JsonNode#hasNonNull(String+fieldName)，它混合了的方法和验证它是否是null值|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|182102|entityMap^0|5|11|1B|1|1L|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

You can use the JsonNode#hasNonNull(String fieldName), it mix the has method and the verification if it is a null value or not

So, I get some JSON values from the server but I don't know if there will be a particular field or not.
So like:
<pre><code>{ &quot;regatta_name&quot;:&quot;ProbaRegatta&quot;,
 &quot;country&quot;:&quot;Congo&quot;,
 &quot;status&quot;:&quot;invited&quot;
}
</code></pre>
And sometimes, there will be an extra field like:
<pre><code>{ &quot;regatta_name&quot;:&quot;ProbaRegatta&quot;,
 &quot;country&quot;:&quot;Congo&quot;,
 &quot;status&quot;:&quot;invited&quot;,
 &quot;club&quot;:&quot;somevalue&quot;
}
</code></pre>
I would like to check if the field named &quot;club&quot; exists so that at parsing I won't get
<blockquote>
org.json.JSONException: No value for club
</blockquote>

How to check if a JSON key exists?

服务器

JSON

因此，我从服务器获得了一些JSON值，但我不知道是否会有特定的字段。就像这样：{ "regatta_name":"ProbaRegatta",  "country":"Congo",  "status":"invited"}有时，还会有一个额外的字段，如：{ "regatta_name":"ProbaRegatta",  "country":"Congo",  "status":"invited"

问如何检查JSON密钥是否存在？
EN

回答 13

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问如何检查JSON密钥是否存在？EN

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问如何检查JSON密钥是否存在？
EN