Jackson Simple Data Binding: Difference between revisions

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=Overview=
=Overview=


Simple data binding extracts data from JSON and initializes an in-memory Java object hierarchy. Unlike the [[Jackson#Tree_Model|tree model]], which uses <tt>JsonNode</tt>s, simple data binding assembles the hierarchy representing the JSON data out of Maps, Lists, Strings, Numbers, Booleans and nulls. A Map/List/String/Number/Boolean hierarchy can be written out as JSON content.
Simple data binding extracts data from JSON and initializes an in-memory Java object hierarchy. Unlike the [[Jackson#Tree_Model|tree model]], which uses <tt>JsonNode</tt>s, simple data binding assembles the hierarchy representing the JSON data out of '''Maps, Lists, Strings, Numbers, Booleans and nulls'''. A Map/List/String/Number/Boolean hierarchy can be written out as JSON content.


=JSON to Java=
=JSON to Java=
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JSON to Java parsing is done by <tt>ObjectMapper.readValue()</tt>, which must be called with an Object.class type:
JSON to Java parsing is done by <tt>ObjectMapper.readValue()</tt>, which must be called with an Object.class type:


<pre>
<syntaxhighlight lang='java'>
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectMapper;


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}
}
...
...
</pre>
</syntaxhighlight>


This is the conversion table:
This is the conversion table:
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It is possible to call readValue() with a more specific type. For example, if the top level JSON value is an Object, readValue() can be called upon a Map.
It is possible to call readValue() with a more specific type. For example, if the top level JSON value is an Object, readValue() can be called upon a Map.


<pre>
<syntaxhighlight lang='java'>
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectMapper;


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Map root = mapper.readValue(inputStream, Map.class);
Map root = mapper.readValue(inputStream, Map.class);
</pre>
</syntaxhighlight>


However, if the top level JSON value is a List, the code above will throw an exception:
However, if the top level JSON value is a List, the code above will throw an exception:
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The Map/List/String/Number/Boolean hierarchy can be written out as JSON by <tt>ObjectMapper.writeValue()</tt>.
The Map/List/String/Number/Boolean hierarchy can be written out as JSON by <tt>ObjectMapper.writeValue()</tt>.


<pre>
<syntaxhighlight lang='java'>
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();


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System.out.println(new String(baos.toByteArray()));
System.out.println(new String(baos.toByteArray()));
</pre>
</syntaxhighlight>


==Java to JSON Code Example==
==Java to JSON Code Example==


{{External|[https://github.com/NovaOrdis/playground/blob/master/json/jackson/05-simple-data-binding-java-to-json/src/main/java/io/novaordis/playground/json/jackson/simpledatabinding/java2json/Main.java Java to JSON Simple Data Binding Example]}}
{{External|[https://github.com/NovaOrdis/playground/blob/master/json/jackson/05-simple-data-binding-java-to-json/src/main/java/io/novaordis/playground/json/jackson/simpledatabinding/java2json/Main.java Java to JSON Simple Data Binding Example]}}

Latest revision as of 00:32, 14 November 2018

Internal

Overview

Simple data binding extracts data from JSON and initializes an in-memory Java object hierarchy. Unlike the tree model, which uses JsonNodes, simple data binding assembles the hierarchy representing the JSON data out of Maps, Lists, Strings, Numbers, Booleans and nulls. A Map/List/String/Number/Boolean hierarchy can be written out as JSON content.

JSON to Java

JSON to Java parsing is done by ObjectMapper.readValue(), which must be called with an Object.class type:

import com.fasterxml.jackson.databind.ObjectMapper;

ObjectMapper mapper = new ObjectMapper();

Object root = mapper.readValue(src, Object.class);

if (root instance of Map) {
    ...
}
else if (root instanceof List) {
    ...
}
...

This is the conversion table:

JSON Type Java Type
object LinkedHashMap<String,Object>
array ArrayList<Object>
string String
number (no fraction) Integer, Long or BigInteger (smallest applicable)
number (fraction) Double (configurable to use BigDecimal)
false Boolean
null null

It is possible to call readValue() with a more specific type. For example, if the top level JSON value is an Object, readValue() can be called upon a Map.

import com.fasterxml.jackson.databind.ObjectMapper;

ObjectMapper mapper = new ObjectMapper();

Map root = mapper.readValue(inputStream, Map.class);

However, if the top level JSON value is a List, the code above will throw an exception:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.LinkedHashMap out of START_ARRAY token

JSON to Java Code Example

JSON to Java Simple Data Binding Example

Generics Support

It is possible to enable generic type information (like Map<String, Object>). For details, see Full Data Binding.

Java to JSON

The Map/List/String/Number/Boolean hierarchy can be written out as JSON by ObjectMapper.writeValue().

ByteArrayOutputStream baos = new ByteArrayOutputStream();

ObjectMapper om = new ObjectMapper();

Map root = ...

om.writeValue(baos, root);

System.out.println(new String(baos.toByteArray()));

Java to JSON Code Example

Java to JSON Simple Data Binding Example