Merge json objects with java

Question

I have two JSON files. I want to combine them into one in such a way that the second file has a greater priority. That is:

if 1 has the property foo and 2 has no property foo, 3 will have the property foo with the value from 1.
if 2 has the property foo and 1 has no property foo, 3 will have the property foo with the value from 2.
if 1 and 2 both have the property foo, 3 will have the property foo with the value from 2.

I need to do this in Java. The final JSON object will be deserialized to a Java object with Google Gson.

Welcome to StackOverflow! Remember to include what you've tried and what you know about why it didn't work. Refer to stackoverflow.com/help/mcve — Nathaniel Ford
– Nathaniel Ford, Commented Mar 4, 2016 at 0:56

Darshan Mehta · Accepted Answer · 2016-03-04 01:34:55Z

3

Here you go:

Gson gson = new Gson();
//read both jsons
Map<String, Object> json1 = gson.fromJson("<json1>", Map.class);
Map<String, Object> json2 = gson.fromJson("<json2>", Map.class);
//create combined json with contents of first json
Map<String, Object> combined = new HashMap<>(json1);
//Add the contents of first json. It will overwrite the values of keys are 
//same. e.g. "foo" of json2 will take precedence if both json1 and json2 have "foo" 
combined.putAll(json2);
gson.toJson(combined);

edited Mar 4, 2016 at 1:34

answered Mar 3, 2016 at 23:02

Darshan Mehta

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2 Comments

Nathaniel Ford Over a year ago

I think this is the reverse of what the OP wanted, but is trivial to correct.

Darshan Mehta Over a year ago

Corrected the logic :)

Oswaldo Junior · Accepted Answer · 2022-08-12 12:38:00Z

To deep-merge JSON files with custom priorities and return as Gson, you should use confectory-datamapper-gson https://github.com/oswaldobapvicjr/confectory/wiki/Download.

Here's how you could do it:

Configuration<JsonObject> json1 = Configuration.<JsonObject>builder()
                .mapper(new GsonJsonObjectMapper())
                .source("classpath://file1.json")
                .precedence(9) // Higher priority
                .build();

Configuration<JsonObject> json2 = Configuration.<JsonObject>builder()
                .mapper(new GsonJsonObjectMapper())
                .source("classpath://file2.json")
                .precedence(1) // Lower priority
                .build();

JsonObject merged = json1.merge(json2).getBean();

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