Use Jackson To Stream Parse an Array of Json Objects

Question

I have a file that contains a json array of objects:

[ { \"test1\": \"abc\" }, { \"test2\": [1, 2, 3] } ]

I wish to use use

Answer 1

This is a late answer that builds on Ian Roberts' answer. You can also use a JsonPointer to find the start position if it is nested into a document. This avoids custom coding the slightly cumbersome streaming token approach to get to the start point. In this case, the basePath is "/", but it can be any path that JsonPointer understands.

Path sourceFile = Paths.get("/path/to/my/file.json");
// Point the basePath to a starting point in the file
JsonPointer basePath = JsonPointer.compile("/");
ObjectMapper mapper = new ObjectMapper();
try (InputStream inputSource = Files.newInputStream(sourceFile);
     JsonParser baseParser = mapper.getFactory().createParser(inputSource);
     JsonParser filteredParser = new FilteringParserDelegate(baseParser,
                    new JsonPointerBasedFilter(basePath), false, false);) {
    // Call nextToken once to initialize the filteredParser
    JsonToken basePathToken = filteredParser.nextToken();
    if (basePathToken != JsonToken.START_ARRAY) {
        throw new IllegalStateException("Base path did not point to an array: found " 
                                       + basePathToken);
    }
    while (filteredParser.nextToken() == JsonToken.START_OBJECT) {
        // Parse each object inside of the array into a separate tree model 
        // to keep a fixed memory footprint when parsing files 
        // larger than the available memory
        JsonNode nextNode = mapper.readTree(filteredParser);
        // Consume/process the node for example:
        JsonPointer fieldRelativePath = JsonPointer.compile("/test1");
        JsonNode valueNode = nextNode.at(fieldRelativePath);
        if (!valueNode.isValueNode()) {
            throw new IllegalStateException("Did not find value at "
                    + fieldRelativePath.toString() 
                    + " after setting base to " + basePath.toString());
        }
        System.out.println(valueNode.asText());
    }
}