How to check whether a given string is valid JSON in Java

Question

How do I validate a JSON string in Java  Or could I parse it using regular expressions

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A solution using the javax json library   import javax json     public boolean isTextJson String text        try           Json createReader new StringReader text   readObject          catch  JsonException ex            try               Json createReader new StringReader text   readArray              catch  JsonException ex2                return false                      return true

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It depends on what you are trying to prove with your validation  Certainly parsing the json as others have suggested is better than using regexes  because the grammar of json is more complicated than can be represented with just regexes   If the json will only ever be parsed by your java code  then use the same parser to validate it   But just parsing won t necessarily tell you if it will be accepted in other environments   e g     many parsers ignore trailing commas in an object or array  but old versions of IE can fail when they hit a trailing comma    Other parsers may accept a trailing comma  but add an undefined null entry after it  Some parsers may allow unquoted property names    Some parsers may react differently to non-ASCII characters in strings    If your validation needs to be very thorough  you could    try different parsers until you find one that fails on all the corner cases I mentioned above or you could probably run jsonlint using javax script      http   npmjs org package jsonlint  or combine using a parser with running jshint using javax script     https   www npmjs org package jshint https   github com webjars jshint

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With Google Gson you can use JsonParser   import com google gson JsonParser   JsonParser parser   new JsonParser    parser parse json string      throws JsonSyntaxException

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You can use WellFormedJson class from Validol declarative validation library   The declaration itself could look like the following   new WellFormedJson      new Unnamed lt  gt  Either right new Present lt  gt  jsonRequestString        The check phase looks like that       Result lt JsonElement gt  result            new WellFormedJson              new Named lt  gt                    vasya                   Either right                      new Present lt  gt                               guest      name     Vadim Samokhin     email     samokhinvadim gmail com      source   1   items       id   1900     id   777                                                                                   result         assertTrue result isSuccessful         assertEquals              guest      name     Vadim Samokhin     email     samokhinvadim gmail com      source   1   items       id   1900     id   777              result value   raw   toString              assertEquals              name     Vadim Samokhin     email     samokhinvadim gmail com              result value   raw   getAsJsonObject   get  guest   toString            It might seem like an overkill for such a simple task  but it shines when you have to validate a complex request  Check out validol s quick start section

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I have found a very simple solution for it    Please first install this library net sf json-lib for it       import net sf json JSONException       import net sf json JSONSerializer       private static boolean isValidJson String jsonStr            boolean isValid   false          try               JSONSerializer toJSON jsonStr               isValid   true            catch  JSONException je                isValid   false                    return isValid             public static void testJson             String vjson       employees         firstName     John       lastName     Doe         firstName     Anna       lastName     Smith         firstName     Peter       lastName     Jones                 String ivjson       employees         firstName     John        lastName     Doe         firstName     Anna       lastName     Smith         firstName     Peter       lastName     Jones                 System out println    isValidJson vjson       true         System out println    isValidJson ivjson       false         Done  Enjoy

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JACKSON Library  One option would be to use Jackson library  First import the latest version  now is     lt dependency gt       lt groupId gt com fasterxml jackson core lt  groupId gt       lt artifactId gt jackson-databind lt  artifactId gt       lt version gt 2 7 0 lt  version gt   lt  dependency gt    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    lt dependency gt       lt groupId gt com google code gson lt  groupId gt       lt artifactId gt gson lt  artifactId gt       lt version gt 2 5 lt  version gt   lt  dependency gt    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

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A bit about parsing   Json  and in fact all languages  use a grammar which is a set of rules that can be used as substitutions  in order to parse json  you need to basically work out those substitutions in reverse  Json is a context free grammar  meaning you can have infinitely nested objects arrays and the json would still be valid  regex only handles regular grammars  hence the  reg  in the name   which is a subset of context free grammars that doesn t allow infinite nesting  so it s impossible to use only regex to parse all valid json  you could use a complicated set of regex s and loops with the assumption that nobody will nest past say  100 levels deep  but it would still be very difficult   if you ARE up for writing your own parser you could make a recursive descent parser after you work out the grammar

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public static boolean isJSONValid String test        try           isValidJSON test           JsonFactory factory   new JsonFactory            JsonParser parser   factory createParser test           while   parser isClosed                  parser nextToken                    catch  Exception e            LOGGER error  exception     e           return false            return true     private static void isValidJSON String test        try           new JSONObject test         catch  JSONException ex            try               LOGGER error  exception     ex               new JSONArray test             catch  JSONException ex1                LOGGER error  exception     ex1               throw new Exception  Invalid JSON                         Above solution covers both the scenarios     duplicate key mismatched quotes or missing parentheses etc

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Check whether a given string is valid JSON in Kotlin  I Converted answer of MByD Java to Kotlin  fun isJSONValid test  String   Boolean       try           JSONObject test         catch  ex  JSONException            try               JSONArray test             catch  ex1  JSONException                return false                      return true

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As you can see  there is a lot of solutions  they mainly parse the JSON  to check it and at the end you will have to parse it to be sure   But  depending on the context  you may improve the performances with a pre-check   What I do when I call APIs  is just checking that the first character is     and the last is      If it s not the case  I don t bother creating a parser

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import static net minidev json JSONValue isValidJson    and then call this function passing in your JSON String

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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

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The answers are partially correct  I also faced the same problem  Parsing the json and checking for exception seems the usual way but the solution fails for the input json something like    outputValueSchemaFormat       sortByIndexInRecord   0  sortOrder  847874874387209 descending  kajhfsadkjh  As you can see the json is invalid as there are trailing garbage characters  But if you try to parse the above json using jackson or gson then you will get the parsed map of the valid json and garbage trailing characters are ignored  Which is not the required solution when you are using the parser for checking json validity    For solution to this problem see here    PS  This question was asked and answered by me

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You can try below code  worked for me   import org json JSONObject   import org json JSONTokener    public static JSONObject parseJsonObject String substring       return new JSONObject new JSONTokener substring

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String jsonInput       mob no     9846716175       Read input Here JSONReader reader   new JSONValidatingReader    Object result   reader read jsonInput   System out println  Validation Success         Please download stringtree-json library

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Here you can find a tool that can validate a JSON file  or you could just deserialize your JSON file with any JSON library and if the operation is successful then it should be valid  google-json for example that will throw an exception if the input it is parsing is not valid JSON

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Here is a working example for strict json parsing with gson library   public static JsonElement parseStrict String json           throws on almost any non-valid json     return new Gson   getAdapter JsonElement class  fromJson json        See also my other detailed answer in How to check if JSON is valid in Java using GSON with more info and extended test case with various non-valid examples

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You could use the  mayBeJSON String str  available in the JSONUtils library

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Using Playframework 2 6  the Json library found in the java api can also be used to simply parse the string  The string can either be a json element of json array  Since the returned value is not of importance here we just catch the parse error to determine that the string is a correct json string or not       import play libs Json       public static Boolean isValidJson String value            try              Json parse value               return true            catch final Exception e               return false

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IMHO  the most elegant way is using the Java API for JSON Processing  JSON-P   one of the  JavaEE standards that conforms to the JSR 374   try StringReader sr   new StringReader jsonStrn         Json createReader sr  readObject      catch JsonParsingException e        System out println  The given string is not a valid json        e printStackTrace        Using Maven  add the dependency on JSON-P    lt dependency gt       lt groupId gt org glassfish lt  groupId gt       lt artifactId gt javax json lt  artifactId gt       lt version gt 1 1 4 lt  version gt   lt  dependency gt    Visit the JSON-P official page for more informations

[java] How to check whether a given string is valid JSON in Java

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