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, "$.store.book");
Does it make sense to think about it this way?
It's the logic for iterating through this that I'm uncertain about.
I would have thought I could define a "Book" pojo and then do something like this:
for (int ctr = 0; ctr < allBooks.size(); ++ ctr) {
Book book = JsonPath.<Book>read(context, ".[" + ctr + "]");
System.out.println("book[" + book + "]");
}
However, this doesn't work. The "read
" method at this point returns a JSONArray
.
The last line in the code sample at https://github.com/jayway/JsonPath#what-is-returned-when is close to what I'm looking at, but this requires parsing the json in every iteration. It seems like the "DocumentContext
" class has "read
" methods that can take a type parameter, but not "JsonPath
".
What are some reasonable strategies for navigating something like this?
JSON path will just return you a list of Maps
as you've no doubt already seen. You need a way to tell it how to map these values to an object - for this you will need a custom configuration. There are other providers like Gson etc., but I've only used Jackson.
Configuration configuration = Configuration
.builder()
.jsonProvider(new JacksonJsonProvider())
.mappingProvider(new JacksonMappingProvider())
.build();
The second step is to specify generic type information with a TypeRef
and pass it along when reading the tag.
List<Book> allBooks = JsonPath.using(configuration)
.parse(context)
.read("$.store.book", new TypeRef<List<Book>>() {});
As a result you get a nice list of Book
objects.