![](\"https:\/\/github.com\/openfaas\/media\/raw\/master\/OpenFaaS_Magnet_3_1_png.png\")
<\/p>\nAt the core of OpenFaaS is a community which is trying to Make Serverless Functions Simple for Docker and Kubernetes. In this blog post I want to show you the new Java template released today which brings Serverless functions to Java developers.<\/p>\n
<\/p>\n
If you’re not familiar with the OpenFaaS CLI, it is used to generate new files with everything you need to start building functions in your favourite programming language.<\/p>\n
The new template made available today provides Java 9 using the OpenJDK, Alpine Linux and gradle<\/a> as a build system. The serverless runtimes for OpenFaaS uses the new accelerated watchdog built out in the OpenFaaS Incubator organisation on GitHub<\/a>.<\/p>\n First of all, set up OpenFaaS on your laptop or the cloud with Kubernetes or Docker Swarm. Follow the quickstart here<\/a><\/p>\n Checklist:<\/p>\n I recommend using Visual Studio Code<\/a> to edit your Java functions. You can also install the Java Extension Pack<\/a> from Microsoft.<\/p>\n You can pull templates from any supported GitHub repository, this means that teams can build their own templates for golden Linux images needed for compliance in the enterprise.<\/p>\n $ faas-cli template pull<\/p>\n You can list all the templates you’ve downloaded like this:<\/p>\n $ faas-cli new –list<\/p>\n … Tip: Before we get started, sign up for a Docker Hub accout<\/a>, or log into your own local Docker registry.<\/p>\n<\/blockquote>\n Below update username=alexellis2 to your Docker Hub user name or private registry address. Now generate a new Java function using the faas-cli which you should have installed.<\/p>\n export username=alexellis2<\/p>\n mkdir -p blog faas-cli new –lang java8 hello-java –prefix=$username<\/p>\n This generates several files:<\/p>\n You then get a function Handler.java and HandlerTest.java file in the .\/src folder.<\/p>\n package com.openfaas.function;<\/p>\n import com.openfaas.model.IHandler; public class Handler implements com.openfaas.model.IHandler {<\/p>\n public IResponse Handle(IRequest req) { return res; Contents of .\/hello-java\/src\/main\/java\/com\/openfaas\/function\/Handler.java<\/em><\/p>\n Now use the faas-cli to build the function, you will see gradle kick in and start downloading the dependencies it needs:<\/p>\n faas-cli build -f hello-java.yml<\/p>\n If you are running on Kubernetes, then you may need to pass the –gateway flag with the URL you used for the OpenFaaS portal. You can also set this in the OPENFAAS_URL environmental-variable.<\/p>\n faas-cli deploy -f hello-java.yml –gateway 127.0.0.1:31112<\/p>\n You can now test the function via the OpenFaaS UI portal, using Postman, the CLI or even curl.<\/p>\n export OPENFAAS_URL=http:\/\/127.0.0.1:31112\/<\/p>\n echo -n “” | faas-cli invoke hello-java<\/p>\n You can now add a third-party dependency such as okhttp which is a popular and easy to use HTTP client. We will create a very rudimentary HTTP proxy which simply fetches the text of any URL passed in via the request.<\/p>\n $ faas-cli new –lang java8 web-proxy<\/p>\n At the end of the dependencies { add the following:<\/p>\n implementation ‘com.squareup.okhttp3:okhttp:3.10.0’ Paste the following into your Handler.java file, this imports the OKHttpClient into scope.<\/p>\n package com.openfaas.function;<\/p>\n import com.openfaas.model.IHandler; import java.io.IOException;<\/p>\n import okhttp3.OkHttpClient;<\/p>\n public class Handler implements IHandler {<\/p>\n public IResponse Handle(IRequest req) { try { okhttp3.Request request = new okhttp3.Request.Builder() okhttp3.Response response = client.newCall(request).execute(); } catch(Exception e) { return res; faas-cli build -f web-proxy.yml Now test it out with a JSON endpoint returning the position of the International Space Station<\/a>.<\/p>\n $ echo -n “http:\/\/api.open-notify.org\/iss-now.json” | faas-cli invoke web-proxy<\/p>\n You can use your preferred JSON library to parse a request in JSON format. This example uses Google’s GSON library and loads a JSON request into a Java POJO.<\/p>\n faas-cli new –lang java8 buildinfo<\/p>\n Within dependencies add:<\/p>\n implementation ‘com.google.code.gson:gson:2.8.5’<\/p>\n package com.openfaas.function;<\/p>\n import com.openfaas.model.IHandler; import com.google.gson.*;<\/p>\n public class Handler implements com.openfaas.model.IHandler {<\/p>\n public IResponse Handle(IRequest req) { Gson gson = new Gson(); res.setBody(“The status of the build is: ” + buildInfo.getStatus());<\/p>\n return res; class BuildInfo { Build, push and deploy your function.<\/p>\n Now invoke it via the CLI:<\/p>\n $ echo ‘{“status”: “queued”}’ | faas invoke buildinfo In this example I will show you how to fetch the manifest file from the OpenFaaS Function Store, we will then deserialize it into an ArrayList and print out the count.<\/p>\n Create a function named deserialize<\/p>\n<\/li>\n Edit build.gradle<\/p>\n<\/li>\n<\/ul>\n Within dependencies add:<\/p>\n implementation ‘com.google.code.gson:gson:2.8.5’ package com.openfaas.function;<\/p>\n import com.openfaas.model.IHandler; import com.google.gson.*; public class Handler implements com.openfaas.model.IHandler {<\/p>\n public IResponse Handle(IRequest req) { Gson gson = new Gson(); int size = functions.size(); public String downloadFromURL(String url) { try { okhttp3.Response response = client.newCall(request).execute(); class Function { Here is the output:<\/p>\n $ echo | faas-cli invoke deserialize ; echo We have now packaged and deployed a Serverless function written in Java. The new OpenFaaS watchdog component keeps your function hot<\/em> and that ensures the JVM is re-used between invocations. This approach enables high-throughput for your code.<\/p>\n Let us know what you think of the new Java template by tweeting to @openfaas<\/a> or join the Slack community<\/a> for one of the special-interest channels like #kubernetes or #templates.<\/p>\n If you would like to use some other JDK version, a different base-image for the Linux container or even a different build-tool like Maven, you can fork the templates repository and add your own variant.<\/p>\n Contributions are welcome, so if you have an enhancement that will benefit the community, please feel free to suggest it over on GitHub.<\/p>\n The Java 8 + Gradle 4.8.1 template is available here:<\/p>\n https:\/\/github.com\/openfaas\/templates\/tree\/master\/template\/java8<\/a><\/p>\nQuickstart<\/h2>\n
\n
Generate a Java function<\/h3>\n
\njava8
\n…<\/p>\n\n
\ncd blog<\/p>\n\n
\nimport com.openfaas.model.IResponse;
\nimport com.openfaas.model.IRequest;
\nimport com.openfaas.model.Response;<\/p>\n
\n Response res = new Response();
\n res.setBody(“Hello, world!”);<\/p>\n
\n }
\n}<\/p>\nBuild and deploy the function<\/h3>\n
Test the function<\/h3>\n
Add a third-party dependency<\/h2>\n
\n
\n
\n implementation ‘com.squareup.okio:okio:1.14.1’<\/p>\n\n
\nimport com.openfaas.model.IResponse;
\nimport com.openfaas.model.IRequest;
\nimport com.openfaas.model.Response;<\/p>\n
\n IResponse res = new Response();<\/p>\n
\n OkHttpClient client = new OkHttpClient();<\/p>\n
\n .url(req.getBody())
\n .build();<\/p>\n
\n String ret = response.body().string();
\n res.setBody(ret);<\/p>\n
\n e.printStackTrace();
\n res.setBody(e.toString());
\n }<\/p>\n
\n }
\n}<\/p>\n\n
\nfaas-cli push -f web-proxy.yml
\nfaas-cli deploy -f web-proxy.yml<\/p>\nParse a JSON request<\/h2>\n
\n
\n
\n
\nimport com.openfaas.model.IResponse;
\nimport com.openfaas.model.IRequest;
\nimport com.openfaas.model.Response;<\/p>\n
\n Response res = new Response();<\/p>\n
\n BuildInfo buildInfo = gson.fromJson(req.getBody(), BuildInfo.class);<\/p>\n
\n }
\n}<\/p>\n
\n private String status = “”;
\n public String getStatus() { return this.status; }
\n}<\/p>\n
\nThe status of the build is: queued<\/p>\nDonwload and parse JSON from an URL<\/h2>\n
\n
\n implementation ‘com.squareup.okhttp3:okhttp:3.10.0’
\n implementation ‘com.squareup.okio:okio:1.14.1’<\/p>\n\n
\nimport com.openfaas.model.IResponse;
\nimport com.openfaas.model.IRequest;
\nimport com.openfaas.model.Response;<\/p>\n
\nimport okhttp3.OkHttpClient;
\nimport com.google.gson.reflect.TypeToken;
\nimport java.util.ArrayList;<\/p>\n
\n Response res = new Response();<\/p>\n
\n String url = “https:\/\/raw.githubusercontent.com\/openfaas\/store\/master\/store.json”;
\n ArrayList<Function> functions = (ArrayList<Function>) gson.fromJson(downloadFromURL(url), new TypeToken<ArrayList<Function>>(){}.getType());<\/p>\n
\n String functionCount = Integer.toString(size);
\n res.setBody(functionCount +” function(s) in the OpenFaaS Function Store”);
\n return res;
\n }<\/p>\n
\n String ret = “{}”;<\/p>\n
\n OkHttpClient client = new OkHttpClient();
\n okhttp3.Request request = new okhttp3.Request.Builder()
\n .url(url)
\n .build();<\/p>\n
\n ret = response.body().string();
\n } catch(Exception e) {
\n e.printStackTrace();
\n System.out.println(e.toString());
\n }
\n return ret;
\n }
\n}<\/p>\n
\n public String Name = “”;
\n}<\/p>\n
\n16 function(s) in the OpenFaaS Function Store<\/p>\nWrapping up<\/h2>\n
Take it further<\/h2>\n