What is the best practice for working with JSON column within Java code? Specifically I am interested in being able to save & query JSON columns in a MySQL DB using hibernate..
@Entity public class MyEntity { private String myField; // this field is a json column public MyEntity() { } } 3 Answers
Answers 1
The mapping between JSON and Java entities JSON.simple maps entities from the left side to the right side while decoding or parsing, and maps entities from the right to the left while encoding.
JSON Java string java.lang.String number java.lang.Number true|false java.lang.Boolean null null array java.util.List object java.util.Map On decoding, the default concrete class of java.util.List is org.json.simple.JSONArray and the default concrete class of java.util.Map is org.json.simple.JSONObject.
Encoding JSON in Java Following is a simple example to encode a JSON object using Java JSONObject which is a subclass of java.util.HashMap. No ordering is provided. If you need the strict ordering of elements, use JSONValue.toJSONString ( map ) method with ordered map implementation such as java.util.LinkedHashMap.
import org.json.simple.JSONObject; class JsonEncodeDemo { public static void main(String[] args){ JSONObject obj = new JSONObject(); obj.put("name", "foo"); obj.put("num", new Integer(100)); obj.put("balance", new Double(1000.21)); obj.put("is_vip", new Boolean(true)); System.out.print(obj); } } On compiling and executing the above program the following result will be generated −
{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"} Following is another example that shows a JSON object streaming using Java JSONObject −
import org.json.simple.JSONObject; class JsonEncodeDemo { public static void main(String[] args){ JSONObject obj = new JSONObject(); obj.put("name","foo"); obj.put("num",new Integer(100)); obj.put("balance",new Double(1000.21)); obj.put("is_vip",new Boolean(true)); StringWriter out = new StringWriter(); obj.writeJSONString(out); String jsonText = out.toString(); System.out.print(jsonText); } } On compiling and executing the above program, the following result is generated −
{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"} Decoding JSON in Java The following example makes use of JSONObject and JSONArray where JSONObject is a java.util.Map and JSONArray is a java.util.List, so you can access them with standard operations of Map or List.
import org.json.simple.JSONObject; import org.json.simple.JSONArray; import org.json.simple.parser.ParseException; import org.json.simple.parser.JSONParser; class JsonDecodeDemo { public static void main(String[] args){ JSONParser parser = new JSONParser(); String s = "[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]"; try{ Object obj = parser.parse(s); JSONArray array = (JSONArray)obj; System.out.println("The 2nd element of array"); System.out.println(array.get(1)); System.out.println(); JSONObject obj2 = (JSONObject)array.get(1); System.out.println("Field \"1\""); System.out.println(obj2.get("1")); s = "{}"; obj = parser.parse(s); System.out.println(obj); s = "[5,]"; obj = parser.parse(s); System.out.println(obj); s = "[5,,2]"; obj = parser.parse(s); System.out.println(obj); }catch(ParseException pe){ System.out.println("position: " + pe.getPosition()); System.out.println(pe); } } } On compiling and executing the above program, the following result will be generated −
The 2nd element of array
{"1":{"2":{"3":{"4":[5,{"6":7}]}}}} Field "1"
{"2":{"3":{"4":[5,{"6":7}]}}} {} [5] [5,2] Answers 2
Use SpringMVC because it implicilty includes jackson and will save your time.
@Autowired MyEntityService myEntityService; @RequestMapping("/myentity") public @ResponseBody MyEntity getEntity(@RequestParam(value = "myField") String myField) { return myEntityService.getMyEntity(myField); } Reference documentation https://www.javadevjournal.com/spring/building-restful-web-services/
Answers 3
There is good library to deal with json types in Hibernate: https://vladmihalcea.com/how-to-map-json-objects-using-generic-hibernate-types/ scroll down to MySQL section to get right example.
And some samples of usage MySQL's JSON API inside query: How to search JSON data in mysql?
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