Strategies for iterating through JsonPath array

Question

I just started exploring JsonPath today. I want to explore not just what's possible to do with it, but some effective strategies.

For instance, let's say I have to iterate through an array contained within one element in the json string.

I'm using the "store" example from https://github.com/jayway/JsonPath#path-examples .

To get the list of books itself, I would imagine I could do something like this:

List<?> allBooks    = JsonPath.<List<?>>read(context, "$.store.book");

Does it make sense to think about it this way?

It's the logic for iterating through this that I'm uncertain about.

I would have thought I could define a "Book" pojo and then do something like this:

    for (int ctr = 0; ctr < allBooks.size(); ++ ctr) {
        Book book   = JsonPath.<Book>read(context, ".[" + ctr + "]");
        System.out.println("book[" + book + "]");
    }

However, this doesn't work. The "read" method at this point returns a JSONArray.

The last line in the code sample at https://github.com/jayway/JsonPath#what-is-returned-when is close to what I'm looking at, but this requires parsing the json in every iteration. It seems like the "DocumentContext" class has "read" methods that can take a type parameter, but not "JsonPath".

What are some reasonable strategies for navigating something like this?

Justas · Accepted Answer · 2017-03-24 15:33:40Z

4

JSON path will just return you a list of Maps as you've no doubt already seen. You need a way to tell it how to map these values to an object - for this you will need a custom configuration. There are other providers like Gson etc., but I've only used Jackson.

Configuration configuration = Configuration
        .builder()
        .jsonProvider(new JacksonJsonProvider())
        .mappingProvider(new JacksonMappingProvider())
        .build();

The second step is to specify generic type information with a TypeRef and pass it along when reading the tag.

List<Book> allBooks = JsonPath.using(configuration)
        .parse(context)
        .read("$.store.book", new TypeRef<List<Book>>() {});

As a result you get a nice list of Book objects.

edited Mar 24, 2017 at 15:33

answered Mar 23, 2017 at 23:08

Justas

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1 Comment

David M. Karr Over a year ago

This works fine, but I notice that the main doc page for JsonPath (github.com/jayway/JsonPath) doesn't even mention TypeRef. I"m guessing using a TypeRef is like using a Class object, but it effectively communicates generic type info. Time for an issue.

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