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List of HashMap into JSONs string with new line in Java

I have to convert a List into jsons string with new line.
Right now the code which i am using converts the List of HashMap into single jsons string. like below:
List<HashMap> mapList= new ArrayList<>();
HashMap hashmap = new HashMap();
hashmap.add("name","SO");
hashmap.add("rollNo","1");
mapList.put(hashmap);
HashMap hashmap1 = new HashMap();
hashmap1.add("name","SO1");
hashmap1.add("rollNo","2");
mapList.put(hashmap1 );
Now I am converting it into jsons string using ObjectMapper and the output would be
ObjectMapper mapper = new ObjectMapper();
String output = mapper.writeValueAsString(mapList);
Output:
[{"name":"SO","rollNo":1},{"name":"SO1","rollNo":2}]
Its working fine but I need the output inthe format shown below, i.e for every HashMap there should be new line in the JSON string.
[{"name":"SO","rollNo":1},
{"name":"SO1","rollNo":2}]

If i clearly understand the question, you can use:
output.replaceAll(",",",\n");
or you can go through each HashMap.Entry and call
mapper.writeValueAsString(entry);
or use configuration
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationConfig.Feature.INDENT_OUTPUT, true);

I suggest a slightly different path, and that is use a custom serializer, as outlined here for example.
It boils down to have your own
public static class MgetSerializer extends JsonSerializer<Mget> {
Which works for List for example.
The point is: I would avoid to "mix" things, as: having a solution where your code writes part of the output, and jackson creates other parts of the output. Rather enable jackson to do exactly what you want it to do.
Beyond that, I find the whole approach a bit dubious in the first place. JSON strings do not care about newlines. So, if you care how things are formatted, rather look into the tools you are using to look at your JSON.
Meaning: why waste your time formatting a string that isn't meant for direct human consumption in the first place? Browser consoles will show you JSON strings in a "folded" way, and any decent editor has similar capabilities these days.
In other words: I think you are investing your energy in the wrong place. JSON is a transport format, and you should only worry about the content you want to transmit, not in (essentially meaningless formatting effects).

You can use String methods to change/replace the output's String. However, this is not correct for json Strings as they may contain commas or other characters that you should escape in the String replace methods.
Alternatively, you should parse the Json String and use JsonNode on the Json as below:
ObjectMapper mapper = new ObjectMapper();
String output = mapper.writeValueAsString(mapList);
JsonNode jsonNode = mapper.readTree(output);
Iterator<JsonNode> iter=jsonNode.iterator();
String result = "[";
while(iter.hasNext()){
result+=iter.next().toString() + ",\n";
}
result =result.substring(0,result.length()-2) + "]";
System.out.println(result);
Result:
[{"rollNo":"1","name":"SO"},
{"rollNo":"2","name":"SO1"}]
This approach will work for String containing characters like comma, for example consider the input hashmap.put("n,,,ame","SO");
The result is:
[{"n,,,ame":"SO","rollNo":"1"},
{"rollNo":"2","name":"SO1"}]
Update: Output updated to include [ and ] and commas between rows.
Update: Fixed the output accordingly

Interpolate JSON values into a string

I am writing an application/class that will take in a template text file and a JSON value and return interpolated text back to the caller.
The format of the input template text file needs to be determined. For example: my name is ${fullName}
Example of the JSON:
{"fullName": "Elon Musk"}
Expected output:
"my name is Elon Musk"
I am looking for a widely used library/formats that can accomplish this.
What format should the template text file be?
What library would support the template text file format defined above and accept JSON values?
Its easy to build my own parser but there are many edge cases that needs to be taken care of and I do not want to reinvent the wheel.
For example, if we have a slightly complex JSON object with lists, nested values etc. then I will have to think about those as well and implement it.

I have always used org.json library. Found at http://www.json.org/.
It makes it really easy to go through JSON Objects.
For example if you want to make a new object:
JSONObject person = new JSONObject();
person.put("fullName", "Elon Musk");
person.put("phoneNumber", 3811111111);
The JSON Object would look like:
{
"fullName": "Elon Musk",
"phoneNumber": 3811111111
}
It's similar to retrieving from the Object
String name = person.getString("fullName");
You can read out the file with BufferedReader and parse it as you wish.
Hopefully I helped out. :)

This is how we do it.
Map inputMap = ["fullName": "Elon Musk"]
String finalText = StrSubstitutor.replace("my name is \${fullName}", inputMap)

You can try this：
https://github.com/alibaba/fastjson
Fastjson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Fastjson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of.

How to consider JSON structure when write into file

I want to save the entities in our program into .json files to get a better connection between backend and our Angular frontend. For this, I wrote some tests and during the execution, the structure is saved in the files as desired.
The structure is sampled by
ObjectMapper objectMapper = new ObjectMapper();
try{
ObjectWriter writer = objectMapper.wrtier(new DefaultPrettyPrinter());
String result = objectMapper.writerWirthDefaultPrettyPrinter().writeValueAsString(new OurObject());
writer.writerValue(new File("path"), result);
}
What I got
"{\r\n \"firstProp\": something,\r\n \"secondProp\": anything,\r\n...
But I want, that the file contains the classical JSON structure to make it better readable, this means:
{
"firstProp": something,
"secondProp": anything,
...
What can I do, to write it in the desired JSON structure?
Thanks for any help
Matthias

You're double-encoding the json string
Remove writeValueAsString and try to directly use writer.writerValue(file, object)
But if you're emitting this from a Java backend, it's typically best practice to serve it from an HTTP request, not as a file to any front-end

Formatting JSON before writing to File

Currently I'm using the Jackson JSON Processor to write preference data and whatnot to files mainly because I want advanced users to be able to modify/backup this data. Jackson is awesome for this because its incredibly easy to use and, apparently performs decently (see here), however the only problem I seem to be having with it is when I run myObjectMapper.writeValue(myFile, myJsonObjectNode) it writes all of the data in the ObjectNode to one line. What I would like to do is to format the JSON into a more user friendly format.
For example, if I pass a simple json tree to it, it will write the following:
{"testArray":[1,2,3,{"testObject":true}], "anotherObject":{"A":"b","C":"d"}, "string1":"i'm a string", "int1": 5092348315}
I would want it to show up in the file as:
{
"testArray": [
1,
2,
3,
{
"testObject": true
}
],
"anotherObject": {
"A": "b",
"C": "d"
},
"string1": "i'm a string",
"int1": 5092348315
}
Is anyone aware of a way I could do this with Jackson, or do I have to get the String of JSON from Jackson and use another third party lib to format it?
Thanks in advance!

try creating Object Writer like this
ObjectWriter writer = mapper.defaultPrettyPrintingWriter();

You need to configure the mapper beforehand as follows:
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationConfig.Feature.INDENT_OUTPUT, true);
mapper.writeValue(myFile, myJsonObjectNode);

As per above mentioned comments this worked for me very well,
Object json = mapper.readValue(content, Object.class);
mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json);
Where content is your JSON string response
Jackson version:2.12

To enable standard indentation in Jackson 2.0.2 and above use the following:
ObjectMapper myObjectMapper = new ObjectMapper();
myObjectMapper.enable(SerializationFeature.INDENT_OUTPUT);
myObjectMapper.writeValue(myFile, myJsonObjectNode)
source:https://github.com/FasterXML/jackson-databind

write json string in JAVA

I am using json developing android sdk.
I found writing json string is annoying, take a look:
post_my_server("{\"cmd\":\"new_comment\"}");
I need to manually escape quotes, is there any clean way to do this?

You can use single quotes "{'cmd':'new_comment'}".
Alternatively, there is free code at http://json.org/java/ for implementing JSON at an object level. It's free as in very permissive, I am no lawyer, but it would seem that the only stipulation is that the software you include it in is good, and not evil.

To create json string use jackson core jars. The code snippet to generate a sample json string ,
JsonFactory jFactory = new JsonFactory();
StringWriter writer = new StringWriter();
/*** write to string ***/
JsonGenerator jsonGenerator = jFactory.createJsonGenerator(writer);
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField("company", [Value]);
jsonGenerator.writeNumberField("salary", [value]);
jsonGenerator.writeEndObject();
jsonGenerator.close();
String jsonString = writer.toString();

I use the jackson json parsers and serializers , they are completely self contained, and allow for reading, writing of any java object to and from json.
Assume you have a file called "user.json" which contains a big json in it....
private static void convert(){
Map<String,Object> userData = mapper.readValue(new File("user.json"), Map.class);
}