Replacing JSON string with another string in java

Question

String str = "{"id":"4ebd7e4f","start_page_ui_id":"","business_unit":["5b65aced"],"props":{"metadata":"[]","postsPerPage":"20","network_id":"1b375ffd"},"render_engine":"twig"}"

Here I want to replace "metadata":"[]" to "metadata":"["key":"value,value1","key1":"value2"]"

for this i tried to replace as

str =str.replace("\"metadata\":\"[\"", "\"metadata\": \"[{\"key\":\"key\",\"val\":\"value,value1\"},{\"key\":\"key1\",\"val\":\"value2\"}");

But it is not getting replaced. I don't understand why?? Can any one please help me to solve this issue.

I want to replace another string "postsPerPage":"20" to "postsPerPage":"6"

for this i tried with

str = str .replace("\"postsPerPage\": \"20\",", "\"postsPerPage\": \"9\",");

Here also the value is not changing.

Check this. You can then reassign values in your Java object, before converting it back to JSON with your desired output. — Junaid
– Junaid, Commented Jun 19, 2018 at 7:30
The content was in a Json format. I have used toString() method to convert into string. After converting it into string I was trying to replace. — Tusar
– Tusar, Commented Jun 19, 2018 at 7:35
That is not a long term solution and is bound to get unwieldy in the near future and is also known as a shortcut! Lol its your choice how you do it, but maintainable and understandable is the better way out! — Junaid
– Junaid, Commented Jun 19, 2018 at 7:37

jannis · Accepted Answer · 2018-06-19 10:58:32Z

1

Use a JSON third-party lib for this, GSON or Jackson being the most popular ones.

For example with GSON (only for small samples! for large blobs of JSON you should consider using the stream API):

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;

public class Main {

    public static void main(String[] args) {
        Gson gson = new Gson();
        String str = "{\"id\":\"4ebd7e4f\",\"start_page_ui_id\":\"\",\"business_unit\":[\"5b65aced\"],\"props\":{\"metadata\":\"[]\",\"postsPerPage\":\"20\",\"network_id\":\"1b375ffd\"},\"render_engine\":\"twig\"}";
        String metadataReplacementJson = "[{\"key\":\"key\",\"val\":\"value,value1\"},{\"key\":\"key1\",\"val\":\"value2\"}]";
        JsonObject jsonObject = gson.fromJson(str, JsonObject.class);

        jsonObject
                .get("props")
                .getAsJsonObject()
                .remove("metadata");

        jsonObject
                .get("props")
                .getAsJsonObject()
                .add("metadata", gson.fromJson(metadataReplacementJson, JsonArray.class));

        System.out.println(gson.toJson(jsonObject));
    }
}

Console output:

{"id":"4ebd7e4f","start_page_ui_id":"","business_unit":["5b65aced"],"props":{"metadata":[{"key":"key","val":"value,value1"},{"key":"key1","val":"value2"}],"postsPerPage":"20","network_id":"1b375ffd"},"render_engine":"twig"}

edited Jun 19, 2018 at 10:58

answered Jun 19, 2018 at 8:33

jannis

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2 Comments

jannis Over a year ago

What is the error you're getting? Anyway you might try removing the property first - see the updated answer

jannis Over a year ago

Also what GSON version are you using?

Junaid · Accepted Answer · 2018-06-19 07:34:29Z

0

Rather a lengthy process, I will outline here what you need to do inorder to manuplate your JSON.

Create a POJO for your JSON.
Parse your JSON and create a POJO Object.
Now manipulate the POJO Object with your new data (Update values, replace etc..)
Write back the fresh JSON.

Libraries: GSON, Jackson are of help here. You can also use online JSON to POJO converters to make your task even more easier.

answered Jun 19, 2018 at 7:34

Junaid

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2 Comments

Thilo Over a year ago

The POJO is not strictly necessary, you can use the JSON tree objects returned by your JSON library directly. But yes, definitely use a JSON parser, don't work on Strings.

Junaid Over a year ago

@Thilo Yes I agree, GSON and Jackson being the best ones so far.

Christopher Jung · Accepted Answer · 2018-06-19 12:16:06Z

0

You have to replace with

"\"metadata\":\"["

not

"\"metadata\":\"[\""

and

"\"postsPerPage\": \"20\","

should be

"\"postsPerPage\":\"20\""

edited Jun 19, 2018 at 12:16

answered Jun 19, 2018 at 7:46

Christopher Jung

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Comments

Umapathi · Accepted Answer · 2018-06-19 12:45:32Z

0

String objects are immutable, so whenever we perform any operation in existing string object at that time a new string object is created.The new Stirng object is not assign to any any String object.

so str = str .replace("\"postsPerPage\": \"20\",", "\"postsPerPage\": \"9\",");

In above line created new object it is automatically eligible for garbage collection.

String str2 = str .replace("\"postsPerPage\": \"20\",", "\"postsPerPage\": \"9\",");

here new String object created. str2 is point to String object.

now you can use str2 will work.

edited Jun 19, 2018 at 12:45

answered Jun 19, 2018 at 12:25

Umapathi

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ErEcTuS · Accepted Answer · 2023-12-14 16:56:24Z

0

For those who are still interested, java 21 has introduced an STR Template

STR."Invalid order quantity : \{qty}";

answered Dec 14, 2023 at 16:56

ErEcTuS

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