Mastering JsonPath: Extract Ordered Objects and Slices from JSON in Java

JSON Data

The article starts with a JSON example representing a store that contains a list of books and a bicycle, then shows how to create a JSONObject from the JSON string in Java.

JSONObject json = JSON.parseObject("{\"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}},\"expensive\":10,\"ss\":[32,32,4,23]}");

Getting an ordered object from the array

Using JsonPath $.store.book[2] retrieves the third book (index starts at 0). The expression $.store.book[-1] returns the last book because a negative index counts from the end.

Indexing begins at 0.

Negative indices select elements from the end of the array.

Object read = JsonPath.read(json, "$.store.book[2]");
output(JSON.parseObject(read.toString()));

An equivalent form using JSONObject directly:

JSONObject read = JsonPath.read(json, "$.store.book[2]");
output(read);

The console output shows the selected book object:

{
  "author":"Herman Melville",
  "price":8.99,
  "isbn":"0-553-21311-3",
  "category":"fiction",
  "title":"Moby Dick"
}

Getting a slice of the array

JsonPath slice syntax mirrors Python's array slicing. $.store.book[:2] returns the first two books, while $.store.book[-2:] returns the last two books.

"[:2]" selects elements from the start up to (but not including) index 2.

"[-2:]" selects the last two elements.

Object slice1 = JsonPath.read(json, "$.store.book[:2]");
output(slice1);
Object slice2 = JsonPath.read(json, "$.store.book[-2:]");
output(slice2);

The console output displays the sliced results, each as a JSON object representing the corresponding books.

{
  "author":"Nigel Rees",
  "price":8.95,
  "category":"reference",
  "title":"Sayings of the Century"
}
...
{
  "author":"J. R. R. Tolkien",
  "price":22.99,
  "isbn":"0-395-19395-8",
  "category":"fiction",
  "title":"The Lord of the Rings"
}