288 lines
16 KiB
Plaintext
288 lines
16 KiB
Plaintext
// Do not edit this file (e.g. go instead to docs/src/main/asciidoc)
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image::https://travis-ci.org/spring-cloud/spring-cloud-stream.svg?branch=master[Build Status, link=https://travis-ci.org/spring-cloud/spring-cloud-stream]
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This project allows a user to develop and run messaging microservices using Spring Integration and run them locally, or in the cloud, or even on Spring XD. Just add `@EnableModule` and run your app as a Spring Boot app (single application context). You just need to connect to the physical broker for the bus, which is automatic if the relevant bus implementation is available on the classpath. The sample uses Redis.
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Here's a sample source module (output channel only):
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[source,java]
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----
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@SpringBootApplication
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@ComponentScan(basePackageClasses=TimerSource.class)
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public class ModuleApplication {
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public static void main(String[] args) throws InterruptedException {
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SpringApplication.run(ModuleApplication.class, args);
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}
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}
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@Configuration
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@EnableModule(Source.class)
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public class TimerSource {
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@Value("${format}")
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private String format;
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@Bean
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@InboundChannelAdapter(value = Source.OUTPUT, autoStartup = "false", poller = @Poller(fixedDelay = "${fixedDelay}", maxMessagesPerPoll = "1"))
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public MessageSource<String> timerMessageSource() {
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return () -> new GenericMessage<>(new SimpleDateFormat(format).format(new Date()));
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}
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}
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----
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The `application.yml` has the mapping from channel names to external broker handles (queues, topics, routing keys, etc. depending on the broker), e.g.
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.application.yml
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----
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---
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spring:
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cloud:
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stream:
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bindings:
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output: ${spring.application.name:ticker}
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----
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`@EnableModule` is parameterized by an interface (in this case `Source`) which declares input and output channels. `Source`, `Sink` and `Processor` are provided off the shelf, but you can define others. Here's the definition of `Source`
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[source,java]
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----
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public interface Source {
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@Output("output")
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MessageChannel output();
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}
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----
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The `@Output` annotation is used to identify output channels (messages leaving the module) and `@Input` is used to identify input channels (messages entering the module). It is optionally parameterized by a channel name - if the name is not provided the method name is used instead. An implementation of the interface is created for you and can be used in the application context by autowiring it, e.g. into a test case:
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[source,java]
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----
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@RunWith(SpringJUnit4ClassRunner.class)
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@SpringApplicationConfiguration(classes = ModuleApplication.class)
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@WebAppConfiguration
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@DirtiesContext
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public class ModuleApplicationTests {
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@Autowired
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private Source source
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@Test
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public void contextLoads() {
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assertNotNull(this.sink.output());
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}
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}
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----
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NOTE: In this case there is only one `Source` in the application context so there is no need to qualify it when it is autowired. If there is ambiguity, e.g. if you are composing one module from some others, you can use `@ModuleChannels` qualifier to inject a specific channel set. The `@ModuleChannels` qualifier takes a parameter which is the class that carries the `@EnableModule` annotation (in this case the `TimerSource`).
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== Multiple Input or Output Channels
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A module can have multiple input or output channels all defined either as `@Input` and `@Output` methods in an interface (preferrable) or as bean definitions. Instead of just one channel named "input" or "output" you can add multiple `MessageChannel` methods annotated `@Input` or `@Output` and the names are converted to external channel names on the broker. The external channel names can be specified as properties that consist of the channel names prefixed with `spring.cloud.stream.bindings` (e.g. `spring.cloud.stream.bindings.input` or `spring.cloud.stream.bindings.output`). External channel names can have a channel type as a colon-separated prefix, and the semantics of the external bus channel changes accordingly (a tap is like a topic). For example, you can have two `MessageChannels` called "output" and "foo" in a module with `spring.cloud.stream.bindings.output=bar` and `spring.cloud.stream.bindings.foo=topic:foo`, and the result is 2 external channels called "bar" and "topic:foo".
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== Samples
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There are several samples, all running on the redis transport (so you need redis running locally to test them).
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NOTE: The main set of samples are "vanilla" in the sense that they are not deployable as XD modules by the current generation (1.x) of XD. You can still interact with an XD system using the appropriate naming convention for input and output channel names (`<stream>.<index>` format).
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* `source` is a Java config version of the classic "timer" module from Spring XD. It has a "fixedDelay" option (in milliseconds) for the period between emitting messages.
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* `sink` is a Java config version of the classic "log" module from Spring XD. It has no options (but some could easily be added), and just logs incoming messages at INFO level.
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* `transform` is a simple pass through logging transformer (just logs the incoming message and passes it on).
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* `double` is a combination of 2 modules defined locally (a source and a sink, so the whole app is self contained).
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* `extended` is a multi-module mashup of `source | transform | transform | sink`, where the modules are defined in the other samples and referred to in this app just as dependencies.
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If you run the source and the sink and point them at the same redis instance (e.g. do nothing to get the one on localhost, or the one they are both bound to as a service on Cloud Foundry) then they will form a "stream" and start talking to each other. All the samples have friendly JMX and Actuator endpoints for inspecting what is going on in the system.
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== Module or App
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Code using this library can be deployed as a standalone app or as an XD module. In standalone mode you app will run happily as a service or in any PaaS (Cloud Foundry, Lattice, Heroku, Azure, etc.). Depending on whether your main aim is to develop an XD module and you just want to test it locally using the standalone mode, or if the ultimate goal is a standalone app, there are some things that you might do differently.
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=== Fat JAR
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You can run in standalone mode from your IDE for testing. To run in production you can create an executable (or "fat") JAR using the standard Spring Boot tooling.
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// To be confirmed...
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// the executable JAR has a load of stuff in it that isn't needed if it's going to be deployed as an XD module. In that case you are better off with the normal JAR packaging provided by Maven or Gradle.
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== Making Standalone Modules Talk to Each Other
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The `[input,output]ChannelName` are used to create physical endpoints in the external broker (e.g. `queue.<channelName>` in Redis).
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For an XD module the channel names are `<group>.<index>` and a source (output only) has `index=0` (the default) and downstream modules have the same group but incremented index, with a sink module (input only) having the highest index. To listen to the output from a running XD module, just use the same "group" name and an index 1 larger than the app before it in the chain.
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> Note: since the same naming conventions are used in XD, you can steal messages from or send messages to an existing XD stream by copying the stream name (to `spring.cloud.streams.group`) and knowing the index of the XD module you want to interact with.
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== Taps
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All output channels can be also tapped so you can also attach a module to a pub-sub endpoint and listen to the tap if you know the module metadata. To tap an existing vanilla module you need to know its `outputChannelName` and the tap name is then `tap:<outputChannelName>`, so you can listen to it on an input channel named `input.topic.tap:<outputChannelName>`. The tap is only active if you explicitly ask for it: you can do that by POSTing to the HTTP endpoint `/taps/<channelName>` (where the channel name can be the internal or external name, e.g. "output" or the external name mapped to the output channel).
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To tap an existing output channel in an XD module you just need to know its group, name and index, e.g.
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```
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spring:
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cloud:
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stream:
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group: tocktap
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name: logger
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index: 0
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tap:
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group: testtock
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name: ticker
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index: 0
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```
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The `spring.cloud.stream.tap` section tells the module runner which topic you want to subscribe to. It creates a new group (a tap can't be in the same group as the one it is tapping) and starts a new index count, in case anyone wants to listen downstream.
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== Building
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:jdkversion: 1.8
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=== Basic Compile and Test
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To build the source you will need to install
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http://maven.apache.org/run-maven/index.html[Apache Maven] v3.0.6 or above and JDK {jdkversion}.
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Spring Cloud uses Maven for most build-related activities, and you
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should be able to get off the ground quite quickly by cloning the
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project you are interested in and typing
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----
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$ mvn install -s .settings.xml
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----
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NOTE: You may need to increase the amount of memory available to Maven by setting
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a `MAVEN_OPTS` environment variable with the value `-Xmx512m -XX:MaxPermSize=128m`
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The `.settings.xml` is only required the first time (or after updates
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to dependencies). It is there to provide repository declarations so
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that those do not need to be hard coded in the project poms.
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For hints on how to build the project look in `.travis.yml` if there
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is one. There should be a "script" and maybe "install" command. Also
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look at the "services" section to see if any services need to be
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running locally (e.g. mongo or rabbit). Ignore the git-related bits
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that you might find in "before_install" since they will be able git
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credentials and you already have those.
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If you need mongo, rabbit or redis, see the README in the https://github.com/spring-cloud-samples/scripts[scripts
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demo repository] for
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instructions. For example consider using the "fig.yml" with
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http://www.fig.sh/[Fig] to run them in Docker containers.
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=== Documentation
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The spring-cloud-build module has a "docs" profile, and if you switch
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that on it will try to build asciidoc sources from
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`src/main/asciidoc`. As part of that process it will look for a
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`README.adoc` and process it by loading all the includes, but not
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parsing or rendering it, just copying it to `${main.basedir}`
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(defaults to `${basedir}`, i.e. the root of the project). If there are
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any changes in the README it will then show up after a Maven build as
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a modified file in the correct place. Just commit it and push the change.
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=== Working with the code
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If you don't have an IDE preference we would recommend that you use
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http://www.springsource.com/developer/sts[Spring Tools Suite] or
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http://eclipse.org[Eclipse] when working with the code. We use the
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http://eclipse.org/m2e/[m2eclipe] eclipse plugin for maven support. Other IDEs and tools
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should also work without issue.
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==== Importing into eclipse with m2eclipse
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We recommend the http://eclipse.org/m2e/[m2eclipe] eclipse plugin when working with
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eclipse. If you don't already have m2eclipse installed it is available from the "eclipse
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marketplace".
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Once the projects are imported into Eclipse you will also need to tell m2eclipse
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to use the `.settings.xml` file for the projects. If you do not do this you may
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see errors many different errors related to the POMs in the projects.
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Open your Eclipse preferences, expand the Maven preferences, and select User Settings.
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In the User Settings field click Browse and navigate to the Spring Cloud project you
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imported selecting the `.settings.xml` file in that project. Click Apply and then OK to
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save the preference changes.
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==== Importing into eclipse without m2eclipse
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If you prefer not to use m2eclipse you can generate eclipse project metadata using the
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following command:
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[indent=0]
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----
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$ mvn eclipse:eclipse
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----
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The generated eclipse projects can be imported by selecting `import existing projects`
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from the `file` menu.
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==== Adding Project Lombok Agent
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Spring Cloud uses [Project
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Lombok](http://projectlombok.org/features/index.html) to generate
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getters and setters etc. Compiling from the command line this
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shouldn't cause any problems, but in an IDE you need to add an agent
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to the JVM. Full instructions can be found in the Lombok website. The
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sign that you need to do this is a lot of compiler errors to do with
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missing methods and fields, e.g.
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[indent=0]
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----
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The method getInitialStatus() is undefined for the type EurekaInstanceConfigBean EurekaDiscoveryClientConfiguration.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka line 120 Java Problem
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The method getInitialStatus() is undefined for the type EurekaInstanceConfigBean EurekaDiscoveryClientConfiguration.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka line 121 Java Problem
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The method setNonSecurePort(int) is undefined for the type EurekaInstanceConfigBean EurekaDiscoveryClientConfiguration.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka line 112 Java Problem
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The type EurekaInstanceConfigBean.IdentifyingDataCenterInfo must implement the inherited abstract method DataCenterInfo.getName() EurekaInstanceConfigBean.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka line 131 Java Problem
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The method getId() is undefined for the type ProxyRouteLocator.ProxyRouteSpec PreDecorationFilter.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/pre line 60 Java Problem
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The method getLocation() is undefined for the type ProxyRouteLocator.ProxyRouteSpec PreDecorationFilter.java /spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/pre line 55 Java Problem
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----
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==== Importing into other IDEs
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Maven is well supported by most Java IDEs. Refer to you vendor documentation.
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== Contributing
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Spring Cloud is released under the non-restrictive Apache 2.0 license,
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and follows a very standard Github development process, using Github
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tracker for issues and merging pull requests into master. If you want
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to contribute even something trivial please do not hesitate, but
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follow the guidelines below.
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=== Sign the Contributor License Agreement
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Before we accept a non-trivial patch or pull request we will need you to sign the
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https://support.springsource.com/spring_committer_signup[contributor's agreement].
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Signing the contributor's agreement does not grant anyone commit rights to the main
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repository, but it does mean that we can accept your contributions, and you will get an
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author credit if we do. Active contributors might be asked to join the core team, and
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given the ability to merge pull requests.
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=== Code Conventions and Housekeeping
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None of these is essential for a pull request, but they will all help. They can also be
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added after the original pull request but before a merge.
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* Use the Spring Framework code format conventions. If you use Eclipse
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you can import formatter settings using the
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`eclipse-code-formatter.xml` file from the
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https://github.com/spring-cloud/build/tree/master/eclipse-coding-conventions.xml[Spring
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Cloud Build] project. If using IntelliJ, you can use the
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http://plugins.jetbrains.com/plugin/6546[Eclipse Code Formatter
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Plugin] to import the same file.
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* Make sure all new `.java` files to have a simple Javadoc class comment with at least an
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`@author` tag identifying you, and preferably at least a paragraph on what the class is
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for.
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* Add the ASF license header comment to all new `.java` files (copy from existing files
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in the project)
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* Add yourself as an `@author` to the .java files that you modify substantially (more
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than cosmetic changes).
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* Add some Javadocs and, if you change the namespace, some XSD doc elements.
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* A few unit tests would help a lot as well -- someone has to do it.
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* If no-one else is using your branch, please rebase it against the current master (or
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other target branch in the main project).
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* When writing a commit message please follow http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[these conventions],
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if you are fixing an existing issue please add `Fixes gh-XXXX` at the end of the commit
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message (where XXXX is the issue number). |