JSOG part of Stefan Goessner's JSONPath implementation. Only basic expressions are supported, specifically dot and bracket navigation.
Any help in expanding JSOG's capabilites in this area are most welcome.
Consider the following JSON object graph, and code sample:
{ "store": {
"book": [
{ "category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{ "category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{ "category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{ "category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
}
}JSOG jsog = ...;
// Standard get-based style
assertEquals("Sayings of the Century",
jsog.get("store")
.get("book")
.get(0)
.get("title").getStringValue());
// On-the-fly compilation
assertEquals("Sayings of the Century",
jsog.path("$.store.book[0].title").getStringValue());
// Pre-compilation
JsogPath pcPath = JsogPath.compile("$.store.book[0].title");
assertEquals("Sayings of the Century",
jsog.path(pcPath).getStringValue());JSOG uses a JsogPath object to navigate between nodes of the object graph.
JSOG allows you to compile the expression on-the-fly, in which case a JsogPath object is created and disposed of after one use. You can also precompile the expression and reuse the JsogPath object.
If you're going to be using the same path often, perhaps in a loop, you should definitely use a precompiled JsogPath.
When using JsogPath, keep in mind that the result of evaluating a JsogPath object is always another JSOG. If you've nagivated to a value node, you will need to use the appropriate get...Value method to retrieve the node's value.
JsogPath has two navigation methods, dot and bracket. Dot navigation can be used when key names are simple alpha-numerics. Bracket navigation is more powerful and can be used to represent any string. Bracket navigation is also used for navigating an array.
Both methods work approximately how they would in JavaScript.
All path expressions begin with the dollar sign character.
Dot navigation is simple and straight forward. You can use dot navigation to walk the object graph of any object-type node. Arrays must use bracket navigation.
Below are some more examples based on the JSON object graph above.
| Left-aligned Path Expression | Left-aligned Value |
| $.store | {"book": [...], "bicycle": ...} |
| $.store.bicycle | {"color": "red", "price": 19.95} |
| $.store.bicycle.color | "red" |
Bracket navigation can be as simple as dot navigation, but it is slightly more verbose. It also supports escape sequences and arrays.
When navigating with brackets, keys are quoted with either single or double quotes.
| Left-aligned Path Expression | Left-aligned Value |
| $['store'] | {"book": [...], "bicycle": ...} |
| $['store'].bicycle | {"color": "red", "price": 19.95} |
| $.store['bicycle'].color | "red" |