Java - Read (JSON) data from S3 object line by line

Question

I have an S3 object that contains JsonL lines. I want to read this object line by line in Java so that I can recursively keep parsing each line (ie, each json) into a POJO and eventually convert the object contents into a list of POJO.

As I understand, AmazonS3.getObject().getObjectContent() returns a stream to the object's content. My next step is to read a line and convert to string which I can then parse into a POJO. I am not sure how to operate on this InputStream to keep obtaining the next line in String format.

Sample data :

{"key1":"val", "key2":"val1", "key3":"val2"}
{"key1":"val3", "key2":"val4", "key3":"val5"}
{"key1":"val6", "key2":"val7", "key3":"val8"}

Answer 1

You have a lot of options for converting the InputStream to String. Take a look here .

 String json = "{\"key1\":\"val\", \"key2\":\"val1\", \"key3\":\"val2\"}\n" +
        "{\"key1\":\"val3\", \"key2\":\"val4\", \"key3\":\"val5\"}\n" +
        "{\"key1\":\"val6\", \"key2\":\"val7\", \"key3\":\"val8\"}";

InputStream in = new ByteArrayInputStream(json.getBytes());

try (BufferedReader buffer = new BufferedReader(new InputStreamReader(in))) {
    buffer.lines().forEach(System.out::println);
}

Answer 2

If you can afford it you can use the jackson libraries and simplify your implementation:

Maven dependency

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

Code

ObjectMapper mapper = new ObjectMapper();
MyObject obj = mapper.readValue(inputStream, MyObject.class);

For applying this logic to each line then loop over each line as explained here and apply the same readValue method which is overloaded for String as well.