How to check whether a given string is valid JSON in Java
JACKSON Library
One option would be to use Jackson library. First import the latest version (now is):
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.7.0</version>
</dependency>
Then, you can implement the correct answer as follows:
import com.fasterxml.jackson.databind.ObjectMapper;
public final class JSONUtils {
private JSONUtils(){}
public static boolean isJSONValid(String jsonInString ) {
try {
final ObjectMapper mapper = new ObjectMapper();
mapper.readTree(jsonInString);
return true;
} catch (IOException e) {
return false;
}
}
}
Google GSON option
Another option is to use Google Gson. Import the dependency:
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.5</version>
</dependency>
Again, you can implement the proposed solution as:
import com.google.gson.Gson;
public final class JSONUtils {
private static final Gson gson = new Gson();
private JSONUtils(){}
public static boolean isJSONValid(String jsonInString) {
try {
gson.fromJson(jsonInString, Object.class);
return true;
} catch(com.google.gson.JsonSyntaxException ex) {
return false;
}
}
}
A simple test follows here:
//A valid JSON String to parse.
String validJsonString = "{ \"developers\": [{ \"firstName\":\"Linus\" , \"lastName\":\"Torvalds\" }, " +
"{ \"firstName\":\"John\" , \"lastName\":\"von Neumann\" } ]}";
// Invalid String with a missing parenthesis at the beginning.
String invalidJsonString = "\"developers\": [ \"firstName\":\"Linus\" , \"lastName\":\"Torvalds\" }, " +
"{ \"firstName\":\"John\" , \"lastName\":\"von Neumann\" } ]}";
boolean firstStringValid = JSONUtils.isJSONValid(validJsonString); //true
boolean secondStringValid = JSONUtils.isJSONValid(invalidJsonString); //false
Please, observe that there could be a "minor" issue due to trailing commas that will be fixed in release 3.0.0
.
A wild idea, try parsing it and catch the exception:
import org.json.*;
public boolean isJSONValid(String test) {
try {
new JSONObject(test);
} catch (JSONException ex) {
// edited, to include @Arthur's comment
// e.g. in case JSONArray is valid as well...
try {
new JSONArray(test);
} catch (JSONException ex1) {
return false;
}
}
return true;
}
This code uses org.json JSON API implementation that is available on github, in maven and partially on Android.