Frequently Asked Questions

General

1. If I use a LinkedHasMap to create a JSONObject the order is not preserved, why ?
2. Json-lib creates empty JSONObjects from my bean class, help me!
3. How do I configure Json-lib as a dependency with Maven2 ?
4. How can I transform a JSON string into a bean with an Enum property ?
5. How can I transform a simple value into a complex one when serializing back to Java ?
6. Json-lib does not find my inner bean, help!
7. I'd like to use XPath-like expressions with JSON, how do I do it ?
8. Where can I get the code for the source code syntax highlighter ?

General

If I use a LinkedHasMap to create a JSONObject the order is not preserved, why ?

The answer is in the JSON specification "An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).".

JSONObject uses a HashMap for its properties representation because the order of its properties is not important.

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Json-lib creates empty JSONObjects from my bean class, help me!

Json-lib uses the JavaBeans convention to inspect your beans and create JSONObjects. If the properties of your beans do not adhere to the convention, the resulting JSONObject will be empty or half empty. You must provide a read/write method pair for each property.

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How do I configure Json-lib as a dependency with Maven2 ?

As Json-lib comes in two flavors (for the time being) you'll have to add <classifier> to your dependency declaration, like the following:

<dependency> <groupId>net.sf.json-lib</groupId> <artifactId>json-lib</artifactId> <version>1.0</version> <classifier>jdk15</classifier> </dependency>

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How can I transform a JSON string into a bean with an Enum property ?

You'll have to register a Morpher that can handle your Enum. Json-lib conveniently includes such a Morpher, so the only thing left to do is configure it and register the Morpher into the MorpherRegistry as follows JSONUtils.getMorpherRegistry().registerMorpher( new EnumMorpher( MyEnum.class ) );

This step is optional since Json-lib 2.2

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How can I transform a simple value into a complex one when serializing back to Java ?

Perhaps you've come across a scenario where you'll want a JSON string like "{'id':1}" transformed back to a Java class, but the catch is that the id property is not a simple value but another class (a complex value), say a wrapper around a primitive long. If you try to serialize such a string back to Java you'll get a ClassCastException. The solution to this problem is registering a Morpher that can handle the input and transform it into an instance of the expected type, in this case the class of the id property.

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Json-lib does not find my inner bean, help!

In order for Json-lib (in fact the PropertyDescriptors) to find and inspect your beans they have to be declared public, and all desired properties must have a public pair of reader/writer. The same applies to beans declared as inner classes (which by the way must also be declared static). Its a good practice to define each bean in its own file, but if you can't please make your inner beans public and static if possible.

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I'd like to use XPath-like expressions with JSON, how do I do it ?

Use JXPath, which is a simple yet powerful project that enables XPath-like expressions to be used with java beans and maps.

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Where can I get the code for the source code syntax highlighter ?

The SintaxHighlighter is availabe from Alex Gorbatchev at http://www.dreamprojections.com/SyntaxHighlighter.

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