In this article, we will create a Java-based HTTP endpoint, make an executable jar out of it, pack it up in Docker and run it locally in no time.<\/p>\n
This article is intended for beginners, who want to looking for a simple walk-through for running a Java application in Docker.<\/p>\n
The vast majority of examples out there describing Java applications in a Dockerized environment include the usage of heavy frameworks like Spring Boot. We want to show here that you don’t need much to get an endpoint running with Java in Docker.<\/p>\n
In fact, we will only use a single library as a dependency:HttpMate core<\/a>. For this example, we’ll use theLowLevel builder of HttpMate<\/a> with a single HTTP handler.<\/p>\n The environment used for this example<\/p>\n The final result is available inthis git repo<\/a>.<\/p>\n Let’s create our initial project structure: <\/p>\n Let’s start with the project’s pom file in the root directory that we called here\u00a0 Here we have:<\/p>\n This is enough to start developing our endpoint in the IDE of choice. Most of those have support for Maven based Java projects.<\/p>\n To start our little server, we will use a simple main method. Let’s create the entry to our application as an Try to run this class and you will see the current time printed.<\/p>\n Let’s make this more functional and separate the part that prints out the time into a lambda function with no argument, a.k.a The convenience interface provided by the low-level HttpMate does not look much different, except instead of returning a HttpMate also provides a simple Java HttpServer wrapper – All we need to do is give it the instance of the HttpMate:<\/p>\n Notice that we have configured our httpHandler to serve the path It’s time to start our Application and make some requests:<\/p>\n Before we put this all into a Dockerfile, we need to package it as a good-old jar.<\/p>\n We’d need two maven plugins for that:maven-compiler-plugin<\/a> andmaven-assembly-plugin<\/a> to build the executable jar.<\/p>\n Once we have that, let’s build our jar: <\/p>\n And run the resulting jar: <\/p>\n Same curl: <\/p>\n The Dockerfile looks quite simple:<\/p>\n It specifies<\/p>\n To build and tag our docker image, we run the following command from the root of the directory:<\/p>\n This will produce a docker image that we can run: <\/p>\n Notice that we are passing the Same curl:<\/p>\n And that is it: we have our simple HTTP endpoint dockerized! <\/p>\n Of course, this is a simplified example, and the endpoint we wrote is not entirely useful. It demonstrates though that you don’t need tons of libraries just to have a running HTTP endpoint, how easy it is to package a runnable jar, use docker with your java application and the basic usage of the low-level HttpMate.<\/p>\n This kind of two-minute setup can be handy when you need to quickly spin a test HTTP server. The other day I was working on a Twitter-bot (stay tuned for an article about that) and I had to debug what my request really looks like on the receiving side. Obviously, I couldn’t ask Twitter to give me a dump of my request, so I needed a simple endpoint, that would output everything possible about my request.<\/p>\n HttpMate’s handler provides access to an object called Using that object, we can print everything there is to the request.<\/p>\n The request path Running our FakeTwitter server and issuing request:<\/p>\n We’ll see the following output in the console (output formatted for readability: it is a map underneath, so you can format it nicely if you so wish)<\/p>\n HttpMate on its own offers much more functionality. However, it is young, is not yet for production use and needs your support! If you like what you read, let us know, by dropping us an email to opensource@envimate.com, or just by trying out HttpMate and leaving a comment in the feedback issue<\/a>.<\/p>\n\n
Organizing the Project<\/h2>\n
\nmkdir -p simple-java-http-docker\/src\/main\/java\/com\/envimate\/examples\/http\n<\/pre>\n
simple-java-http-docker<\/code>: <\/p>\n\n<project xmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\" xmlns=\"http:\/\/maven.apache.org\/POM\/4.0.0\"\n xsi:schemaLocation=\"http:\/\/maven.apache.org\/POM\/4.0.0 http:\/\/maven.apache.org\/maven-v4_0_0.xsd\">\n <modelVersion>4.0.0<\/modelVersion>\n\n <groupId>com.envimate.examples<\/groupId>\n <artifactId>simple-java-http-docker<\/artifactId>\n <version>0.0.1<\/version>\n\n <dependencies>\n <dependency>\n <groupId>com.envimate.httpmate<\/groupId>\n <artifactId>core<\/artifactId>\n <version>1.0.21<\/version>\n <\/dependency>\n <\/dependencies>\n<\/project>\n<\/pre>\n
\n
Application Entrypoint<\/h2>\n
Application.java<\/code> file in the directory src\/main\/java\/com\/envimate\/examples\/http<\/code> that will for now just output the time to the console.<\/p>\n\npackage com.envimate.examples.http;\n\nimport java.time.LocalDateTime;\nimport java.time.format.DateTimeFormatter;\n\npublic final class Application {\n public static void main(String[] args) {\n final LocalDateTime time = LocalDateTime.now();\n final String dateFormatted = time.format(DateTimeFormatter.ISO_TIME);\n System.out.println(\"current time is \" + dateFormatted);\n }\n}\n<\/pre>\nSupplier<\/code>.<\/p>\n\npackage com.envimate.examples.http;\n\nimport java.time.LocalDateTime;\nimport java.time.format.DateTimeFormatter;\nimport java.util.function.Supplier;\n\npublic final class Application {\n public static void main(String[] args) {\n Supplier handler = () -> {\n final LocalDateTime time = LocalDateTime.now();\n final String dateFormatted = time.format(DateTimeFormatter.ISO_TIME);\n return \"current time is \" + dateFormatted;\n };\n\n System.out.println(handler.get());\n }\n}\n<\/pre>\nString<\/code>, that String<\/code> is set to the response, alongside with the indication that everything went well (a.k.a. response code 200).\nfinal HttpHandler httpHandler = (request, response) -> {\n final LocalDateTime time = LocalDateTime.now();\n final String dateFormatted = time.format(DateTimeFormatter.ISO_TIME);\n\n response.setStatus(200);\n response.setBody(\"current time is \" + dateFormatted);\n};\n<\/pre>\nPureJavaEndpoint<\/code> – that would allow you to start an endpoint without any further dependency.<\/p>\n\npackage com.envimate.examples.http;\n\nimport com.envimate.httpmate.HttpMate;\nimport com.envimate.httpmate.convenience.endpoints.PureJavaEndpoint;\nimport com.envimate.httpmate.convenience.handler.HttpHandler;\n\nimport java.time.LocalDateTime;\nimport java.time.format.DateTimeFormatter;\n\nimport static com.envimate.httpmate.HttpMate.anHttpMateConfiguredAs;\nimport static com.envimate.httpmate.LowLevelBuilder.LOW_LEVEL;\n\npublic final class Application {\n public static void main(String[] args) {\n final HttpHandler httpHandler = (request, response) -> {\n final LocalDateTime time = LocalDateTime.now();\n final String dateFormatted = time.format(DateTimeFormatter.ISO_TIME);\n\n response.setStatus(200);\n response.setBody(\"current time is \" + dateFormatted);\n };\n\n final HttpMate httpMate = anHttpMateConfiguredAs(LOW_LEVEL)\n .get(\"\/time\", httpHandler)\n .build();\n PureJavaEndpoint.pureJavaEndpointFor(httpMate).listeningOnThePort(1337);\n }\n}\n<\/pre>\n\/time<\/code>, when invoked with method GET.<\/p>\n\ncurl http:\/\/localhost:1337\/time\ncurrent time is 15:09:34.458756\n<\/pre>\n
Building the Jar<\/h2>\n
\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<project xmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\" xmlns=\"http:\/\/maven.apache.org\/POM\/4.0.0\"\n xsi:schemaLocation=\"http:\/\/maven.apache.org\/POM\/4.0.0 http:\/\/maven.apache.org\/maven-v4_0_0.xsd\">\n <modelVersion>4.0.0<\/modelVersion>\n\n <groupId>com.envimate.examples<\/groupId>\n <artifactId>simple-java-http-docker<\/artifactId>\n <version>0.0.1<\/version>\n\n <dependencies>\n <dependency>\n <groupId>com.envimate.httpmate<\/groupId>\n <artifactId>core<\/artifactId>\n <version>1.0.21<\/version>\n <\/dependency>\n <\/dependencies>\n\n <build>\n <plugins>\n <plugin>\n <groupId>org.apache.maven.plugins<\/groupId>\n <artifactId>maven-compiler-plugin<\/artifactId>\n <version>3.8.1<\/version>\n <configuration>\n <release>${java.version}<\/release>\n <source>${java.version}<\/source>\n <target>${java.version}<\/target>\n <\/configuration>\n <\/plugin>\n <plugin>\n <groupId>org.apache.maven.plugins<\/groupId>\n <artifactId>maven-assembly-plugin<\/artifactId>\n <executions>\n <execution>\n <phase>package<\/phase>\n <goals>\n <goal>single<\/goal>\n <\/goals>\n <configuration>\n <archive>\n <manifest>\n <mainClass>\n com.envimate.examples.http.Application\n <\/mainClass>\n <\/manifest>\n <\/archive>\n <descriptorRefs>\n <descriptorRef>jar-with-dependencies<\/descriptorRef>\n <\/descriptorRefs>\n <\/configuration>\n <\/execution>\n <\/executions>\n <\/plugin>\n <\/plugins>\n <\/build>\n<\/project>\n<\/pre>\n\nmvn clean verify\n<\/pre>\n
\njava -jar target\/simple-java-http-docker-0.0.1-jar-with-dependencies.jar\n<\/pre>\n
\ncurl http:\/\/localhost:1337\/time\ncurrent time is 15:14:42.992563\n<\/pre>\n
Dockerizing the Jar<\/h2>\n
\nFROM openjdk:12\n\nADD target\/simple-java-http-docker-0.0.1-jar-with-dependencies.jar \/opt\/application.jar\n\nEXPOSE 1337\n\nENTRYPOINT exec java -jar \/opt\/application.jar\n<\/pre>\n
\n
FROM<\/code>: which image to use as a base. We will use an openjdk image.<\/li>\nADD<\/code>: the jar we want to the directory we want<\/li>\nEXPOSE<\/code>: the port we are listening on<\/li>\nENTRYPOINT<\/code>: to the command, we want to execute<\/li>\n<\/ul>\n\ndocker build --tag simple-java-http-docker .\n<\/pre>\n
\ndocker run --publish 1337:1337 simple-java-http-docker\n<\/pre>\n
--publish<\/code> parameter, which indicates that the exposed 1337 port, is available under the 1337 port of the machine.<\/p>\n\ncurl http:\/\/localhost:1337\/time\ncurrent time is 15:23:04.275515\n<\/pre>\n
The Icing<\/h2>\n
MetaData<\/code> which is pretty much what it’s called – the meta-data of your request, meaning everything available about your request.<\/p>\n\npublic final class FakeTwitter {\n public static void main(String[] args) {\n final HttpMate httpMate = HttpMate.aLowLevelHttpMate()\n .callingTheHandler(metaData -> {\n System.out.println(metaData);\n })\n .forRequestPath(\"\/*\").andRequestMethods(GET, POST, PUT)\n .build();\n\n PureJavaEndpoint.pureJavaEndpointFor(httpMate).listeningOnThePort(1337);\n }\n}\n<\/pre>\n\/time<\/code> is now replaced with a pattern, capturing all paths, and we can add all the HTTP methods we are interested in.<\/p>\n\ncurl -XGET http:\/\/localhost:1337\/some\/path\/with?someParameter=someValue\n<\/pre>\n
\n{\n PATH=Path(path=\/some\/path\/with),\n BODY_STRING=,\n RAW_QUERY_PARAMETERS={someParameter=someValue},\n QUERY_PARAMETERS=QueryParameters(\n queryParameters={\n QueryParameterKey(key=someParameter)=QueryParameterValue(value=someValue)\n }\n ),\n RESPONSE_STATUS=200,\n RAW_HEADERS={Accept=*\/*,\n Host=localhost:1337,\n User-agent=curl\/7.61.0},\n RAW_METHOD=GET,\n IS_HTTP_REQUEST=true,\n PATH_PARAMETERS=PathParameters(pathParameters={}),\n BODY_STREAM=sun.net.httpserver.FixedLengthInputStream@6053cef4,\n RESPONSE_HEADERS={},\n HEADERS=Headers(headers={HeaderKey(value=user-agent)=HeaderValue(value=curl\/7.61.0),\n HeaderKey(value=host)=HeaderValue(value=localhost:1337),\n HeaderKey(value=accept)=HeaderValue(value=*\/*)}),\n CONTENT_TYPE=ContentType(value=null),\n RAW_PATH=\/some\/path\/with,\n METHOD=GET,\n LOGGER=com.envimate.httpmate.logger.Loggers$$Lambda$17\/0x000000080118f040@5106c12f,\n HANDLER=com.envimate.examples.http.FakeTwitter$$Lambda$18\/0x000000080118f440@68157191\n}\n<\/pre>\nFinal Words<\/h2>\n