Hi I am try to parse some JSON by GSON which used number as the key.
I reference the post but it give some error and I don't know why.
How to convert json objects with number as field key in Java?
I also see the post but still cannot solve my problem.
"Expected BEGIN_OBJECT but was STRING at line 1 column 1"
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;
public class Main {
public static void main(String[] args) {
Gson gson = new Gson();
Type type = new TypeToken<HashMap<String, HashMap<String, String>>>() {}.getType();
Map<String, Map<String, String>> map = gson.fromJson("./src/main/resources/input.json", type);
}
}
The json file is
{
"1":{"id":"1"}
}
The fromJson method doesn't receive a filename, it receives an actual JSON: look at the docs here
But there is an overload that receives a Reader instead:
try (FileReader reader = new FileReader("./src/main/resources/input.json"))
{
map = gson.fromJson(reader, type)
}
catch (...) { ... }
Related
I have a JSON file(it contains an array of JSON objects.)
I am trying to read it object by object.
Each object I need to convert it to a LinkedHashMap<String,String> where both the key and value are strings. Note that even if the JSON objects contain a non-string value(Integer/Boolean), I want my LinkedHashMap to contain a string.
This is my JSON file (films.json):
[
{
"name": "Fight Club",
"year": 1999,
}
]
Now, this has 1 object. I want to convert it to a LinkedHashMap<String,String>.
So for the above example, my LinkedHashMap should contain(for the 1st JSON object) :
"name" : "Fight CLub"
"year" : "1999"
Notice how the year is String in the LinkedHashMap and not Integer.
This is what I tried.
Map<String, Object> myLinkedHashMap;
JsonParser jsonParser = new JsonFactory().createParser(new File("films.json"));
jsonParser = new JsonFactory().createParser(new File(filePath));
jsonParser.nextToken();
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
while(jsonParser.nextToken() != JsonToken.END_ARRAY){
myLinkedHashMap = mapper.readValue(jsonParser, LinkedHashMap.class);
}
The variable myLinkedHashMap will contain a key/value pair for an object in my JSON file.
But the problem is that for 'year' of the JSON file, I am getting Integer in the LinkedHashMap as the JSON file also contains Integer.
Instead, I want the Integer as String in the LinkedHashMap.
Please help me get String in the LinkedHashMap instead of Integer.
Note: The solution should be generic to other data types also.
So if the JSON object contains boolean true, then my LinkedHashMap should contain "true".
You can construct map type using TypeFactory and constructMapType method to tell exactly what do you need from readValue method. See below example:
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.MapType;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import org.springframework.util.Assert;
import java.io.File;
import java.util.LinkedHashMap;
public class JsonMapApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
JsonParser jsonParser = mapper.getFactory().createParser(jsonFile);
jsonParser.nextToken();
MapType mapType = mapper.getTypeFactory().constructMapType(LinkedHashMap.class, String.class, String.class);
while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
LinkedHashMap<String, String> map = mapper.readValue(jsonParser, mapType);
map.forEach((k, v) -> {
Assert.isInstanceOf(String.class, v);
System.out.println(k + " -> " + v + " (" + v.getClass().getName() + ")");
});
}
}
}
Above code prints:
name -> Fight Club (java.lang.String)
year -> 1999 (java.lang.String)
Change
Map<String, Object> myLinkedHashMap;
to
Map<String, String> myLinkedHashMap;
I'm creating a Spring application on backend and my main goal is to manage properties (add/update/delete) in *.properties file. I want to convert this file to JSON and then manipulate it from UI application.
Is there any possibility to convert structure like this:
a.x=1
a.y=2
b.z=3
To JSON like this:
{
"a": {
"x": 1,
"y": 2
},
"b": {
"z": 3
}
}
I found solution to use GSON library, but it creates for me flat structure, not hierarchical, code I used:
Properties props = new Properties();
try (FileInputStream in = new FileInputStream(classPathResource.getFile())) {
props.load(in);
}
String json = new GsonBuilder().enableComplexMapKeySerialization().create().toJson(props);
Is here someone who was facing same problem and maybe found a working project for this? Maybe GSON library can do that?
This solution does involve loads of work, but you will get what you want to achieve using the below code, basically, the idea is to split the key based on the single dot and then create a JsonObject if the same first key is found.
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Properties;
import org.json.JSONObject;
import com.fasterxml.jackson.annotation.JsonIgnore;
public class SOTest {
public static void main(String[] args) throws IOException {
JSONObject jsonObject = new JSONObject();
FileReader fileReader = new FileReader(new File("C:\\Usrc\\main\\java\\Sample.properties"));
Properties properties = new Properties();
properties.load(fileReader);
Iterator<Entry<Object, Object>> iterator = properties.entrySet().iterator();
while (iterator.hasNext()) {
Entry<Object, Object> entry = iterator.next();
String value = (String) entry.getKey();
String[] values = value.split("\\.");
JSONObject opt = jsonObject.optJSONObject(values[0]);
if(opt!=null) {
opt.put(values[1],entry.getValue());
}else {
JSONObject object = new JSONObject();
object.put(values[1], entry.getValue());
jsonObject.put(values[0], object);
}
}
System.out.println(jsonObject.toString());
}
}
Output
{"a":{"x":"1","y":"3"},"b":{"z":"10"}}
I am trying to convert my hashmap to a JSON pretty print output.
I tried GSON and believe there is some issue with it handling string as inputs inside a map, is there any other way to do this?
Map<String, String> map = new LinkedHashMap();
Gson gson = new GsonBuilder().enableComplexMapKeySerialization().setPrettyPrinting().create();
map.put("Intro", Map_to_String);
map.put("Output", String_Val);
System.out.println(gson.toJson(map));
Output:
{
"Intro": {\"No\":0,\"Cast\":2},
"Output": "123"
}
Required Output:
{
"Intro": {"No":0,"Cast":2},
"Output": "123"
}
You need to deserialise Map_to_String back to object - Map in this case and after that serialise again.
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;
import java.util.LinkedHashMap;
import java.util.Map;
public class GsonApp {
public static void main(String[] args) {
Map<String, Object> map = new LinkedHashMap<>();
Gson gson = new GsonBuilder()
.enableComplexMapKeySerialization()
.setPrettyPrinting()
.create();
String jsonString = "{\"No\":0,\"Cast\":2}";
Type mapType = new TypeToken<Map<String, String>>() {}.getType();
map.put("Intro", gson.fromJson(jsonString, mapType));
map.put("Output", "123");
System.out.println(gson.toJson(map));
}
}
Prints:
{
"Intro": {
"No": "0",
"Cast": "2"
},
"Output": "123"
}
I am struggling with this issue and I can't find an answer anywhere. Ihave a .jsonlist file formatted like this :
example.jsonlist
{"op_author":1, "op_name":2}
{"op_author":3, "op_name":4}
{"op_author":5, "op_name":6}
I would like to parse it into a Java object, but I can't find how to do it with Gson or json-simple libraries since it is not formated like a json object.
Here is what I tried so far :
Modele.java
public class Modele {
private String op_author, op_name;
}
JsonListToJava.java
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class JsonListToJava {
public static void main(String[] args) throws IOException {
try(Reader reader = new InputStreamReader(JsonListToJava.class.getResourceAsStream("example.jsonlist"), "UTF-8")){
Gson gson = new GsonBuilder().create();
Modele p = gson.fromJson(reader, Modele.class);
System.out.println(p);
}
}
}
But I get this error :
Exception in thread "main" com.google.gson.JsonSyntaxException:
com.google.gson.stream.MalformedJsonException: Use
JsonReader.setLenient(true) to accept malformed JSON at line 2 column ...
JSON libraries are usually designed to work with valid JSONs.
In your case you can read the file line by line, then parse:
try(BufferedReader reader = new BufferedReader(new InputStreamReader(JsonListToJava.class.getResourceAsStream("example.jsonlist"), "UTF-8"))){
Gson gson = new GsonBuilder().create();
Stream<String> lines = reader.lines();
lines.forEach((line) -> {
Model p = gson.fromJson(line, Model.class);
System.out.println(p);
});
}
I have a JSON I want a to convert it to a HashMap. I have the following code -
ObjectMapper mapper = new ObjectMapper();
Map<String, String> jsonData = new HashMap<String, String>();
jsonData = mapper.readValue(userPropertyJson, new TypeReference<HashMap<String,String>>(){});
it is working fine if the input JSON is
{"user":1, "entity": "email"}
but fails when the JSON is as below -
{"user":1, "entity": ["email","fname","lname","phone"]}
How do I map to HashMap for array also?
Declare a generic HashMap with String as a key and Object as a value , since you don't know the type of value exactly.
Map<String, Object>
And beware of assigning wrong types while retrieving data
Use Map<String, Object>. Example
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonParser {
public static void main(String[] args) {
String userPropertyJson = "{\"user\":1, \"entity\": [\"email\",\"fname\",\"lname\",\"phone\"]}";
ObjectMapper mapper = new ObjectMapper();
try {
Map<String, Object> jsonData = new HashMap<String, Object>();
jsonData = mapper.readValue(userPropertyJson, new TypeReference<HashMap<String,Object>>(){});
System.out.println(jsonData);
} catch (JsonParseException e) {
System.out.println(e.getMessage());
} catch (JsonMappingException e) {
System.out.println(e.getMessage());
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
If you know in advance that your json will always have the same format (a String key mapped to a List<String>, either with a single element or with many elements), then you could use the ACCEPT_SINGLE_VALUE_AS_ARRAY deserialization feature:
ObjectMapper mapper = new ObjectMapper()
.enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);
String jsonWithArray =
"{\"user\": 1, \"entity\": [\"email\", \"fname\", \"lname\", \"phone\"]}";
Map<String, List<String>> map1 =
mapper.readValue(
jsonWithArray,
new TypeReference<HashMap<String, List<String>>>() {});
System.out.println(map1); // {user=[1], entity=[email, fname, lname, phone]}
String jsonWithoutArray = "{\"user\": 1, \"entity\": \"email\"}";
Map<String, List<String>> map2 =
mapper.readValue(
jsonWithoutArray,
new TypeReference<HashMap<String, List<String>>>() {});
System.out.println(map2); // {user=[1], entity=[email]}
This enables you to either have an array for the values in your json, or a single element.
Check out http://www.jsonschema2pojo.org/
It allows you to convert json to java object automatically. I use it when I need to create DTOs from a web service for which I don't have java mapping or SDK.