We have a scenario in which we need to retrieve the description info for EC2 instances running on AWS. To accomplish this, we are using the AWS Java SDK. In 90% of our use case, the com.amazonaws.services.ec2.model.Instance class is exactly what we need. However, there is also a small use-case where it would be beneficial to get the raw XML describing the instance. That is, the XML data before it is converted into the Instance object. Is there any way to obtain both the Instance object and the XML string using the AWS Java SDK? Is there a way to manually convert from one to the other? Or, would we be forced to make a separate call using HttpClient or something similar to get the XML data?
Make an EC2Client by adding request handler and override the beforeUnmarshalling() method like below
AmazonEC2ClientBuilder.standard().withRegion("us-east-1")
.withRequestHandlers(
new RequestHandler2() {
#Override
public HttpResponse beforeUnmarshalling(Request<?> request, HttpResponse httpResponse) {
// httpResponse.getContent() is the raw xml response from AWS
// you either save it to a file or to a XML document
return new HTTPResponse(...);
// if you consumed httpResponse.getContent(), you need to provide new HTTPResponse
}
}
).build():
If you have xml (e.g. from using AWS rest API directly), then you can use com.amazonaws.services.ec2.model.transform.* classes to convert xml to java objects. Unfortunately, it only provides classes required for SDK itself. So you, for example, can convert raw XML to an Instance using InstanceStaxUnmarshaller, but can't convert Instance to XML unless you write such converter.
Here is an example how to parse an Instance XML:
XMLEventReader eventReader = XMLInputFactory.newInstance().createXMLEventReader(new StringReader(instanceXml));
StaxUnmarshallerContext suc = new StaxUnmarshallerContext(eventReader, new TreeMap<>());
InstanceStaxUnmarshaller isu = new InstanceStaxUnmarshaller();
Instance i = isu.unmarshall(suc);
System.out.println(i.toString());
You probably can try to intercept raw AWS response, so that you can keep raw XML while still using SDK most of the time. But I wouldn't call that easy as it will require quite a bit of coding.
You could use JAXB.marshal like following. JAXB (Java Architecture for XML Binding) could convert Java object to / from XML file.
StringWriter sw = new StringWriter();
JAXB.marshal(instance, sw);
String xmlString = sw.toString();
You can use AWS rest API to replace Java SDK. A bonus will be slight performance gain because you'll not send statistic data to Amazon as the SDK does.
Related
I am using AWS Textract to OCR images and create a searchable PDF as outlined in this AWS blog post.
The basic request code looks like this:
AmazonTextractClientBuilder builder = AmazonTextractClientBuilder.standard();
DetectDocumentTextRequest request = new DetectDocumentTextRequest()
.withDocument(new Document()
.withBytes(imageBytes));
DetectDocumentTextResult result = client.detectDocumentText(request);
List<Block> blocks = result.getBlocks()
This works out great however I would also like to write out and keep the original response JSON that contains all the information on what was detected where etc.
Is there a way to get to the response JSON using the JAVA SDK?
AWS doesn't return the response JSON to you in raw form. The assumption may have been that it wouldn't be required once it has been converted to a DetectDocumentTextResult object.
You are able to convert the DetectDocumentTextResult object to JSON (example) which should provide identical values. Note that the variable names will not be identical (e.g.: DocumentMetadata vs documentMetadata) but the values of those variables will be the same.
EDIT: I changed my mind. I would find a way to generate the Java class and load the JSON as an object of that class.
I just discovered that exists a variant of JSON called JSON-LD.
It seems to me a more structured way of defining JSON, that reminds me XML with an associated schema, like XSD.
Can I create a Java class from JSON-LD, load it at runtime and use it to convert JSON-LD to an instantiation of that class?
I read the documentation of both the implementations but I found nothing about it. Maybe I read them bad?
Doing a Google search brought me to a library that will decode the JSON-LD into an "undefined" Object.
// Open a valid json(-ld) input file
InputStream inputStream = new FileInputStream("input.json");
// Read the file into an Object (The type of this object will be a List, Map, String, Boolean,
// Number or null depending on the root object in the file).
Object jsonObject = JsonUtils.fromInputStream(inputStream);
// Create a context JSON map containing prefixes and definitions
Map context = new HashMap();
// Customise context...
// Create an instance of JsonLdOptions with the standard JSON-LD options
JsonLdOptions options = new JsonLdOptions();
// Customise options...
// Call whichever JSONLD function you want! (e.g. compact)
Object compact = JsonLdProcessor.compact(jsonObject, context, options);
// Print out the result (or don't, it's your call!)
System.out.println(JsonUtils.toPrettyString(compact));
https://github.com/jsonld-java/jsonld-java
Apparently, it can take it from just a string as well, as if reading it from a file or some other source. How you access the contents of the object, I can't tell. The documentation seems to be moderately decent, though.
It seems to be an active project, as the last commit was only 4 days ago and has 30 contributors. The license is BSD 3-Clause, if that makes any difference to you.
I'm not in any way associate with this project. I'm not an author nor have I made any pull requests. It's just something I found.
Good luck and I hope this helped!
see this page: JSON-LD Module for Jackson
The question can seem simple, but I didn't find a good answer yet. I need to send a JSon structure (build with an unspecified libretry I'm currently developing) from a Servlet to a remote page.
I'm interested in the best way to send the structure.
I mean, in my Servlet, inside the doPost() event, how should I manage the send?
I was thinking about 2 scenarios:
try (PrintWriter out = response.getWriter()) {
out.print(myJSon.toString(); // <- recursive function that overrides
// toString() and returns the entire JSon
// structure
} (...)
or
try (OutputStream os = response.getOutputStream()) {
myJSon.write(os, StandardCharsets.UTF8); // <- function that
// recursively writes chunk of my JSon structure
// in a BufferWriter created inside the root write function
// forcing UTF-8 encoding
} (...)
Or something different, if there's a better approch.
Note that the JSon structure contains an array of objects with long text fields (descriptions with more than 1000 characterd), so it can be quite memory consuming.
For why I'm not using standard JSon libreries, it's because I don't know them and I don't know if I can trust them yet. And also I don't know if I will be able to install them on the production server.
Thanks for your answers.
From your question i see multiple points to adress:
How to send your JSon
What JSon library can you use
How to use the library in production
How to send your JSon
From your code this seems to be an HTTP response rather than a POST on your Servlet so you need to know how to send a JSON string as an HTTP response's body
Do you use a framework for your web server or are you handling everything manually ? If you use a framework it usually does it for you, just pass the JSON String
If your doing it manually:
try (PrintWriter pw = response.getWriter()) {
pw.write(myJson.toString());
}
or
try (OutputStream os = response.getOutputStream()) {
os.write(myJson.toString().getBytes());
}
Both are valid, see Writer or OutputStream?
Your JSON's size shouldn't matter given what your saying, it's just text so it won't be big enough to matter.
What libraries can you use
There are a lot of JSON libraries for Java, mainly:
Jackson
GSon
json-io
Genson
Go for the one you prefer, there will be extensive documentation and resources all over google
How to use in production
If you are not sure you are able to install dependencies on the production server, you can always create an uber-jar (See #Premraj' answer)
Basically, you bundle the dependency in your Jar
Using Gson is good way to send json
Gson gson = new Gson();
String jsonData = gson.toJson(student);
PrintWriter out = response.getWriter();
try {
out.println(jsonData);
} finally {
out.close();
}
for detail json response from servlet in java
I have a couchbase database that is shared between multiple applications, storing documents as json. I cannot seem to get data into my java app, since it appears to be dependent on native java binary serialization.
This code:
CouchbaseClient client = new CouchbaseClient(hosts,"bucket","");
System.out.println((String)client.get("someKey"));
results in
net.spy.memcached.transcoders.SerializingTranscoder: Failed to decompress data
java.util.zip.ZipException: Not in GZIP format
since it is trying to deserialize by default. I notice that I can provide my own transcoder, but I really only want the raw string data so I can json parse it myself using gson or whatever. None of the available transcoders seem to give me this.
The couchbase docs have an example for setting json, but none for reading it. How are people reading json into java?
First off, this problem will go away soon in that the Couchbase "2.0 SDKs" implement common flags between each other so this kind of problem doesn't come up. Michael's blogs are a good read if you want to see what's happening here. The reason for the problem in the first place is that in the 1.x series, Couchbase was trying to stay compatible with existing application code and memcached. In the memcached world, the clients were all written by different people at different times.
Based on the exception, I believe you're probably trying to read an item stored by .NET. I have a sample transcoder you can use for this from a few weeks ago.
Make sure you are using latest CB java client:
<dependencies>
<dependency>
<groupId>com.couchbase.client</groupId>
<artifactId>couchbase-client</artifactId>
<version>1.4.4</version>
</dependency>
</dependencies>
see: Couchbase Java Client Library 1.4
I have my service that uses CB client running just fine. Here is how I create client:
CouchbaseConnectionFactoryBuilder cfb = new CouchbaseConnectionFactoryBuilder();
cfb.setOpTimeout(10000);
cfb.setOpQueueMaxBlockTime(5000);
CouchbaseClient client = new CouchbaseClient(cfb.buildCouchbaseConnection(baseURIs, bucketName, ""));
And here is an example how I get a raw string and convert it to POJOs:
MyPOJO get(CouchbaseClient client, String key)
{
com.google.gson.Gson gson = new com.google.gson.Gson();
String jsonValue = (String) client.get(key);
return gson.fromJson(jsonValue, MyPOJO.class);
}
Also, update your question with the sample JSON doc that causing this issue. Perhaps it has something to do with the format of the document itself.
I asked something like this previously, but upon re-reading my original post, it was not easy to understand what I was really asking. I have the following situation. We have (or at least I'm trying to get working) a custom file upload procedure that will take in the file, a set number of 'known' metadata values (and they will always be there), as well as potentially an unknown number of additional metadata values. The service that exists currently uses the Jersey framework (1.16)
I currently have both client and server code that handles dealing with the file upload portion and the known metadata values (server code below)
#POST
#Path("asset/{obfuscatedValue0}/")
#Consumes(MediaType.MULTIPART_FORM_DATA)
public UUID uploadBlob(#PathParam("obfuscatedValue0") Integer obfuscatedValue0,
#FormDataParam("obfuscatedValue1") String obfuscatedValue1,
#FormDataParam("obfuscatedValue2") String obfuscatedValue2,
#FormDataParam("obfuscatedValue3") String obfuscatedValue3,
#FormDataParam("obfuscatedValue4") String obfuscatedValue4,
#FormDataParam("obfuscatedValue5") String obfuscatedValue5,
#FormDataParam("file") InputStream uploadedInputStream) {
.....
}
...and excerpt of client code:
Builder requestBuilder = _storageService
.path("asset")
.path(obfuscatedValue0.toString())
.type(MediaType.MULTIPART_FORM_DATA)
.accept(MediaType.APPLICATION_JSON);
FormDataMultiPart part = new FormDataMultiPart()
.field("file", is, MediaType.TEXT_PLAIN_TYPE) // 'is' is an inputstream from earlier in code.
.field("obfuscatedValue1", obfuscatedValue1)
.field("obfuscatedValue2", obfuscatedValue2)
.field("obfuscatedValue3", obfuscatedValue3)
.field("obfuscatedValue4", obfuscatedValue4)
.field("obfuscatedValue5", obfuscatedValue5);
storedAsset = requestBuilder.post(UUID.class, part);
However, I need to pass a map of additional parameters that will have an unknown number of values/names. From what I've seen, there is no easy way to do this using the FormDataParam annotation like my previous example.
Based upon various internet searches related to Jersey file uploads, I've attempted to convert it to use MultivaluedMap with the content type set to "application/x-www-form-urlencoded" so it resembles this:
#POST
#Path("asset/{value}/")
#Consumes("application/x-www-form-urlencoded")
public UUID uploadBlob(#PathParam(value), MultivaluedMap<String,String> formParams) {
....
}
It's my understanding that MultivaluedMap is intended to obtain a general map of form parameters (and as such, cannot play nicely together in the same method bearing #FormDataParam annotations.) If I can pass all this information from the Client inside some sort of map, I think I can figure out how to handle parsing the map to grab and 'doMagic()' on the data to get what I want done; I don't think I'll have a problem there.
What I AM fairly confused about is how to format the request client-side code when using this second method within the jersey framework. Can anyone provide some guidance for the situation, or some suggestions on how to proceed? I'm considering trying the solution proposed here and developing a custom xml adapter to deal with this situation, and sending xml instead of multipart-form-data but I'm still confused how this would interact with the InputStream value that will need to be passed. It appears the examples with MultivaluedMap that I've seen only deal with String data.