JarCastingJson Streaming / JsonPath Matcher
Streaming Json is fast but at the cost of lack of context (previous node / attribute...) and matcher. Matching a json with a path barely more complex than parent/child is cumbersome and imply to implement context saving and matching.
Thanks to JsonPath, a string expression will help to parse the json.
Field matcher
The following code:
try(InputStream is = new FileInputStream("foo.json")){
JsonFactory factory = new JsonFactory();
JsonParser parser = factory.createParser(is);
while(parser.nextToken() != null){
if (JsonToken.FIELD_NAME == parser.getCurrentToken() && "foo".equals(parser.getText())){
//Do something
}
}
}
Can be replaced with a more friendly lambda stream based approach:
JsonStreams.stream("src/test/resources/foo.json")
.field("foo")
.forEach(c -> {
//Do something
});
JsonPath matcher
Things can get tough when the path is complex
Pseudo java code:
try(InputStream is = new FileInputStream("foo.json")){
JsonFactory factory = new JsonFactory();
JsonParser parser = factory.createParser(is);
// Pseudo class to handle a json path
JsonPath jsonPath = new JsonPath();
while(parser.nextToken() != null) {
jsonPath.manageToken(parser.getCurrentToken());
if ("$.foo.bar".equals(jsonPath.toString())) {
//Do something
}
}
}
The JsonPath matcher allows to keep the code clean and focused:
JsonStreams.stream("foo.xml")
.jsonPath("$.foo.bar")
.forEach(c -> {
//Do something
});
Predicates
All matchers are Java 8 Predicate that can be combined.
JsonStreams.consumer("foo.xml"))
.match(jsonPath("@.book").or(jsonPath("@.movie")), c -> {})
.consume();
See the Predicates helper for the list of supported predicates.
Nested Consumer and Streamer
Consumer and Streamer can be nested.
In the following example, a first stream match all the wikipedia page tag. Starting from this tag, a nester consumer extract the title, id, timestamp and contributor name:
try (InputStream fis = new FileInputStream("src/test/resources/wikipedia.json");
JsonStreams.stream("wikipedia.json")
.jsonPath("$.page")
.map(context -> {
Page page = new Page();
context.partialConsumer()
.matchJsonPath("@.title", c -> page.title = c.getText())
.matchJsonPath("@.id", c -> page.id = c.getText())
.matchJsonPath("@.revision.timestamp", c -> page.lastRevision = c.getText())
.matchJsonPath("@.revision.contributor.username", c -> page.lastContributor = c.getText())
.consume();
return page;
})
.forEach(p -> p.toString())
Supported JsonPath
TBD