This little code example shows how a Jsonnet config using object-oriented features can be transliterated (in a structure-preserving manner) to use the object-oriented features of Java. Not all Jsonnet programs can be converted to Java because Jsonnet has mixins and virtual inner classes. Execution order is also different, as Jsonnet is lazy and Java is eager. Likewise, Java programs cannot all be converted to Jsonnet because they have mutable state and I/O.

However said all this, there is a significant overlap between the two languages. This example fits within that overlap.

jsonnet sub-template.jsonnet

We pipe into jsonnet - to pretty-print the output JSON.

javac *.java && java Test | jsonnet -

The translation is as as follows:

• Everything is typed as Object, as Jsonnet is dynamically typed. Everything is public, as is implicit in Jsonnet.
• Jsonnet arrays are Object[], and primitives are Boolean / Double / String.
• Jsonnet objects are singleton instances of named Java classes that extend JsonnetObject.
• Jsonnet fields become Java methods with no parameters (fields are virtual in Jsonnet).
• Jsonnet hidden field status is represented with a method nonHiddenFields which returns a set of field names. Other fields are considered hidden.
• There are 2 liberties taken -- output strings are not escaped properly, and the JSON is printed on a single line instead of pretty-printed with indenting.

The Java code has a number of auxiliary framework functions to provide Jsonnet functionality that is implicit in the Jsonnet language.

• The Test class chooses an object and manifests it to stdout.
• The JsonnetValue class implements manifestation, as a visitor over possible JSON values that builds JSON strings. For objects, it iterates over the non-hidden fields and manifests each value by reflectively calling that function.

For reference, the JSON that should be output is given in sub-template.json