[BAEL-5553] Check whether a string is valid JSON in Java (#12136)

* [BAEL-5553] Check whether a string is valid JSON in Java

* [BAEL-5553] Move implementation to json-2 package

* [BAEL-5553] Move mapper creation outside method

json-2/pom.xml

@@ -14,6 +14,11 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>org.json</groupId>
+            <artifactId>json</artifactId>
+            <version>${json.version}</version>
+        </dependency>
         <dependency>
             <groupId>com.alibaba</groupId>
             <artifactId>fastjson</artifactId>
@@ -148,6 +153,7 @@
         <jsoniter.version>0.9.23</jsoniter.version>
         <moshi.version>1.9.2</moshi.version>
         <fastjson.version>1.2.21</fastjson.version>
+        <json.version>20211205</json.version>
     </properties>
 
 </project>

json-2/src/main/java/com/baeldung/jsonvalidation/GsonValidator.java

@@ -0,0 +1,32 @@
+package com.baeldung.jsonvalidation;
+
+import java.io.IOException;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParser;
+import com.google.gson.JsonSyntaxException;
+import com.google.gson.TypeAdapter;
+
+public class GsonValidator {
+
+    final TypeAdapter<JsonElement> strictAdapter = new Gson().getAdapter(JsonElement.class);
+
+    public boolean isValid(String json) {
+        try {
+            JsonParser.parseString(json);
+        } catch (JsonSyntaxException e) {
+            return false;
+        }
+        return true;
+    }
+
+    public boolean isValidStrict(String json) {
+        try {
+            strictAdapter.fromJson(json);
+        } catch (JsonSyntaxException | IOException e) {
+            return false;
+        }
+        return true;
+    }
+}

json-2/src/main/java/com/baeldung/jsonvalidation/JacksonValidator.java

@@ -0,0 +1,18 @@
+package com.baeldung.jsonvalidation;
+
+import com.fasterxml.jackson.core.JacksonException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class JacksonValidator {
+
+    final ObjectMapper mapper = new ObjectMapper();
+
+    public boolean isValid(String json) {
+        try {
+            mapper.readTree(json);
+        } catch (JacksonException e) {
+            return false;
+        }
+        return true;
+    }
+}

json-2/src/main/java/com/baeldung/jsonvalidation/JsonValidator.java

@@ -0,0 +1,30 @@
+package com.baeldung.jsonvalidation;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+public class JsonValidator {
+
+    public boolean isValidObject(String json) {
+        try {
+            new JSONObject(json);
+        } catch (JSONException e) {
+            return false;
+        }
+        return true;
+    }
+
+    public boolean isValidJson(String json) {
+        try {
+            new JSONObject(json);
+        } catch (JSONException e) {
+            try {
+                new JSONArray(json);
+            } catch (JSONException ne) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

json-2/src/test/java/com/baeldung/jsonvalidation/GsonValidatorUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.jsonvalidation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class GsonValidatorUnitTest {
+
+    private final GsonValidator validator = new GsonValidator();
+
+    @Test
+    public void givenValidObjectJson_whenValidatingNonStrict_thenValid() {
+        String json = "{\"email\": \"example@com\", \"name\": \"John\"}";
+        assertTrue(validator.isValid(json));
+    }
+
+    @Test
+    public void givenValidArrayJson_whenValidatingNonStrict_thenValid() {
+        String json = "[{\"email\": \"example@com\", \"name\": \"John\"},{\"email\": \"example1@com\", \"name\": \"Bob\"}]";
+        assertTrue(validator.isValid(json));
+    }
+
+    @Test
+    public void givenInvalidJson_whenValidatingNonStrict_thenValid() {
+        String json = "Invalid_Json";
+        assertTrue(validator.isValid(json));
+    }
+
+    @Test
+    public void givenInvalidJson_whenValidatingStrict_thenInvalid() {
+        String json = "Invalid_Json";
+        assertFalse(validator.isValidStrict(json));
+    }
+}

json-2/src/test/java/com/baeldung/jsonvalidation/JacksonValidatorUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.jsonvalidation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class JacksonValidatorUnitTest {
+
+    private final JacksonValidator validator = new JacksonValidator();
+
+    @Test
+    public void givenValidObjectJson_whenValidating_thenValid() {
+        String json = "{\"email\": \"example@com\", \"name\": \"John\"}";
+        assertTrue(validator.isValid(json));
+    }
+
+    @Test
+    public void givenValidArrayJson_whenValidating_thenValid() {
+        String json = "[{\"email\": \"example@com\", \"name\": \"John\"},{\"email\": \"example1@com\", \"name\": \"Bob\"}]";
+        assertTrue(validator.isValid(json));
+    }
+
+    @Test
+    public void givenInvalidJson_whenValidating_thenInvalid() {
+        String json = "Invalid_Json";
+        assertFalse(validator.isValid(json));
+    }
+}

json-2/src/test/java/com/baeldung/jsonvalidation/JsonValidatorUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.jsonvalidation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class JsonValidatorUnitTest {
+
+    private final JsonValidator validator = new JsonValidator();
+
+    @Test
+    public void givenValidObjectJson_whenValidatingObject_thenValid() {
+        String json = "{\"email\": \"example@com\", \"name\": \"John\"}";
+        assertTrue(validator.isValidObject(json));
+    }
+
+    @Test
+    public void givenInvalidJson_whenValidating_thenInvalid() {
+        String json = "Invalid_Json";
+        assertFalse(validator.isValidObject(json));
+    }
+
+    @Test
+    public void givenValidArrayJson_whenValidatingObject_thenInvalid() {
+        String json = "[{\"email\": \"example@com\", \"name\": \"John\"},{\"email\": \"example1@com\", \"name\": \"Bob\"}]";
+        assertFalse(validator.isValidObject(json));
+    }
+
+    @Test
+    public void givenValidJson_whenValidatingJson_thenValid() {
+        String json = "[{\"email\": \"example@com\", \"name\": \"John\"},{\"email\": \"example1@com\", \"name\": \"Bob\"}]";
+        assertTrue(validator.isValidJson(json));
+    }
+}