Develop Reference

TCP Socket Server setup for receive/process/reply

This is a new question following up on this older question and answer (specifically the comment that says "don't comment on old answers, ask a new question"), as well as these examples in GitHub.
I know the answer and examples are minimal working "trivial examples", but I don't know enough about how "things work in Spring" (or should work) to understand how to decompose those generic, trivial examples into separate servers and clients that suit my purpose. I currently have a working Spring-Boot daemon application that is client to / calls on (without any "spring integration") a legacy daemon application over a TCP Socket connection. It's all working, running in production.
But now I am tasked with migrating the legacy daemon to Spring Boot too. So I only need to configure and set up a cached/pooled TCP connection "socket listener" on the server-side. However, the "client parts" of the existing (self contained) examples confuse me. In my case the "client side" (the existing Spring Boot daemon) is not going to change and is a separate app on a separate server, I only need to set up / configure the "server-side" of the socket connection (the "legacy-daemon freshly migrated to Spring Boot" daemon).
I've copied this example configuration (exactly) into my legacy-migration project
#EnableIntegration
#IntegrationComponentScan
#Configuration
public static class Config {
#Value(${some.port})
private int port;
#MessagingGateway(defaultRequestChannel="toTcp")
public interface Gateway {
String viaTcp(String in);
}
#Bean
#ServiceActivator(inputChannel="toTcp")
public MessageHandler tcpOutGate(AbstractClientConnectionFactory connectionFactory) {
TcpOutboundGateway gate = new TcpOutboundGateway();
gate.setConnectionFactory(connectionFactory);
gate.setOutputChannelName("resultToString");
return gate;
}
#Bean
public TcpInboundGateway tcpInGate(AbstractServerConnectionFactory connectionFactory) {
TcpInboundGateway inGate = new TcpInboundGateway();
inGate.setConnectionFactory(connectionFactory);
inGate.setRequestChannel(fromTcp());
return inGate;
}
#Bean
public MessageChannel fromTcp() {
return new DirectChannel();
}
#MessageEndpoint
public static class Echo {
#Transformer(inputChannel="fromTcp", outputChannel="toEcho")
public String convert(byte[] bytes) {
return new String(bytes);
}
#ServiceActivator(inputChannel="toEcho")
public String upCase(String in) {
return in.toUpperCase();
}
#Transformer(inputChannel="resultToString")
public String convertResult(byte[] bytes) {
return new String(bytes);
}
}
#Bean
public AbstractClientConnectionFactory clientCF() {
return new TcpNetClientConnectionFactory("localhost", this.port);
}
#Bean
public AbstractServerConnectionFactory serverCF() {
return new TcpNetServerConnectionFactory(this.port);
}
}
...and the project will start on 'localhost' and "listen" on port 10000. But, when I connect to the socket from another local app and send some test text, nothing returns until I shut down the socket listening app. Only after the socket listening app starts shutting down does a response (the correct 'uppercased' result) go back to the sending app.
How do I get the "listener" to return a response to the "sender" normally, without shutting down the listener's server first?
Or can someone please provide an example that ONLY shows the server-side (hopefully annotation based) setup? (Or edit the example so the server and client are clearly decoupled?)

Samples usually contain both the client and server because it's easier that way. But there is nothing special about breaking apart the client and server sides. Here's an example using the Java DSL:
#SpringBootApplication
public class So60443538Application {
public static void main(String[] args) {
SpringApplication.run(So60443538Application.class, args);
}
#Bean
public IntegrationFlow server() {
return IntegrationFlows.from(Tcp.inboundGateway(Tcp.netServer(1234)))
.transform(Transformers.objectToString()) // byte[] -> String
.<String, String>transform(p -> p.toUpperCase())
.get();
}
}
#SpringBootApplication
public class So604435381Application {
private static final Logger LOG = LoggerFactory.getLogger(So604435381Application.class);
public static void main(String[] args) {
SpringApplication.run(So604435381Application.class, args);
}
#Bean
public IntegrationFlow client() {
return IntegrationFlows.from(Gate.class)
.handle(Tcp.outboundGateway(Tcp.netClient("localhost", 1234)))
.transform(Transformers.objectToString())
.get();
}
#Bean
#DependsOn("client")
public ApplicationRunner runner(Gate gateway) {
return args -> LOG.info(gateway.exchange("foo"));
}
}
interface Gate {
String exchange(String in);
}
2020-02-28 09:14:04.158 INFO 35974 --- [ main] com.example.demo.So604435381Application : FOO

How to stop and start jms listener

I'm using Spring and I have a JMS queue to send messages from client to server. I'd like to stop the messages from being sent when the server is down, and resend them when it's back up.
I know it was asked before but I can't make it work. I created a JmsListener and gave it an ID, but I cannot get it's container in order to stop\start it.
#Resource(name="testId")
private AbstractJmsListeningContainer _probeUpdatesListenerContainer;
public void testSendJms() {
_jmsTemplate.convertAndSend("queue", "working");
}
#JmsListener(destination="queue", id="testId")
public void testJms(String s) {
System.out.println("Received JMS: " + s);
}
The container bean is never created. I also tried getting it from the context or using #Autowired and #Qualifier("testId") with no luck.
How can I get the container?

You need #EnableJms on one of your configuration classes.
You need a jmsListenerContainerFactory bean.
You can stop and start the containers using the JmsListenerEndpointRegistry bean.
See the Spring documentation.

If you use CachingConnectionFactory in your project, you need to call the resetConnection() method between stop and restart, otherwise the old physical connection will remain open, and it will be reused when you restart.

I used JmsListenerEndpointRegistry. Here's my example. I hope this will help.
Bean configuration in JmsConfiguration.java. I changed default autostart option.
#Bean(name="someQueueScheduled")
public DefaultJmsListenerContainerFactory odsContractScheduledQueueContainerFactory() {
DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
ActiveMQConnectionFactory cf = new ActiveMQConnectionFactory(someActiveMQ);
Map<String, Class<?>> typeIds = new HashMap<>();
typeIds.put(SomeDTO);
factory.setMessageConverter(messageConverter(Collections.unmodifiableMap(typeIds)));
factory.setPubSubDomain(false);
factory.setConnectionFactory(cf);
factory.setAutoStartup(false);
return factory;
}
Invoke in SomeFacade.java
public class SomeFacade {
#Autowired
JmsListenerEndpointRegistry someUpdateListener;
public void stopSomeUpdateListener() {
MessageListenerContainer container = someUpdateListener.getListenerContainer("someUpdateListener");
container.stop();
}
public void startSomeUpdateListener() {
MessageListenerContainer container = someUpdateListener.getListenerContainer("someUpdateListener");
container.start();
}
}
JmsListener implementation in SomeService.java
public class SomeService {
#JmsListener(id = "someUpdateListener",
destination = "${some.someQueueName}",
containerFactory ="someQueueScheduled")
public void pullUpdateSomething(SomeDTO someDTO) {
}
}

How to start H2 TCP server on Spring Boot application startup?

I'm able to start the H2 TCP server (database in a file) when running app as Spring Boot app by adding following line into the SpringBootServletInitializer main method:
#SpringBootApplication
public class NatiaApplication extends SpringBootServletInitializer {
public static void main(String[] args) {
Server.createTcpServer().start();
SpringApplication.run(NatiaApplication.class, args);
}
}
But if I run the WAR file on Tomcat it doesn't work because the main method is not called. Is there a better universal way how to start the H2 TCP server on the application startup before beans get initialized? I use Flyway (autoconfig) and it fails on "Connection refused: connect" probably because the server is not running. Thank you.

This solution works for me. It starts the H2 server if the app runs as Spring Boot app and also if it runs on Tomcat. Creating H2 server as a bean did not work because the Flyway bean was created earlier and failed on "Connection refused".
#SpringBootApplication
#Log
public class NatiaApplication extends SpringBootServletInitializer {
public static void main(String[] args) {
startH2Server();
SpringApplication.run(NatiaApplication.class, args);
}
#Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
startH2Server();
return application.sources(NatiaApplication.class);
}
private static void startH2Server() {
try {
Server h2Server = Server.createTcpServer().start();
if (h2Server.isRunning(true)) {
log.info("H2 server was started and is running.");
} else {
throw new RuntimeException("Could not start H2 server.");
}
} catch (SQLException e) {
throw new RuntimeException("Failed to start H2 server: ", e);
}
}
}

Yup, straight from the documentation, you can use a bean reference:
<bean id = "org.h2.tools.Server"
class="org.h2.tools.Server"
factory-method="createTcpServer"
init-method="start"
destroy-method="stop">
<constructor-arg value="-tcp,-tcpAllowOthers,-tcpPort,8043" />
There's also a servlet listener option that auto-starts/stops it.
That answers your question, but I think you should probably be using the embedded mode instead if it's deploying along with your Spring Boot application. This is MUCH faster and lighter on resources. You simply specify the correct URL and the database will start:
jdbc:h2:/usr/share/myDbFolder
(straight out of the cheat sheet).

There's a caveat that hasn't been considered in the other answers. What you need to be aware of is that starting a server is a transient dependency on your DataSource bean. This is due to the DataSource only needing a network connection, not a bean relationship.
The problem this causes is that spring-boot will not know about the h2 database needing to be fired up before creating the DataSource, so you could end up with a connection exception on application startup.
With the spring-framework this isn't a problem as you put the DB server startup in the root config with the database as a child. With spring boot AFAIK there's only a single context.
To get around this what you can do is create an Optional<Server> dependency on the data-source. The reason for Optional is you may not always start the server (configuration parameter) for which you may have a production DB.
#Bean(destroyMethod = "close")
public DataSource dataSource(Optional<Server> h2Server) throws PropertyVetoException {
HikariDataSource ds = new HikariDataSource();
ds.setDriverClassName(env.getProperty("db.driver"));
ds.setJdbcUrl(env.getProperty("db.url"));
ds.setUsername(env.getProperty("db.user"));
ds.setPassword(env.getProperty("db.pass"));
return ds;
}

For WAR packaging you can do this:
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
#Override
protected Class<?>[] getRootConfigClasses() {
return null;
}
#Override
protected Class<?>[] getServletConfigClasses() {
Server.createTcpServer().start();
return new Class[] { NatiaApplication.class };
}
#Override
protected String[] getServletMappings() {
return new String[] { "/" };
}
}

You can do like this:
#Configuration
public class H2ServerConfiguration {
#Value("${db.port}")
private String h2TcpPort;
/**
* TCP connection to connect with SQL clients to the embedded h2 database.
*
* #see Server
* #throws SQLException if something went wrong during startup the server.
* #return h2 db Server
*/
#Bean
public Server server() throws SQLException {
return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", h2TcpPort).start();
}
/**
* #return FlywayMigrationStrategy the strategy for migration.
*/
#Bean
#DependsOn("server")
public FlywayMigrationStrategy flywayMigrationStrategy() {
return Flyway::migrate;
}
}

spring bean startup/shutdown order configuration (start h2 db as server)

I'd like to create configuration/bean to automatically start H2DB in my development profile. I'd like to have it running as a tcp server. It's needed to be started before any DataSource configuration. Can someone tell me how to achieve this?
Wha have I done is
#Profile("h2")
#Component
public class H2DbServerConfiguration implements SmartLifecycle {
private static final Logger logger = LoggerFactory.getLogger(H2DbServerConfiguration.class);
private Server server;
#Override
public boolean isAutoStartup() {
return true;
}
#Override
public void stop(Runnable callback) {
stop();
new Thread(callback).start();
}
#Override
public void start() {
logger.debug("############################################");
logger.debug("############################################");
logger.debug("STARTING SERVER");
logger.debug("############################################");
logger.debug("############################################");
try {
server = Server.createTcpServer("-web", "-webAllowOthers", "-webPort", "8082").start();
} catch (SQLException e) {
throw new RuntimeException("Unable to start H2 server", e);
}
}
#Override
public void stop() {
logger.debug("############################################");
logger.debug("############################################");
logger.debug("STOPPING SERVER");
logger.debug("############################################");
logger.debug("############################################");
if (server != null)
if (server.isRunning(true))
server.stop();
}
#Override
public boolean isRunning() {
return server != null ? server.isRunning(true) : false;
}
#Override
public int getPhase() {
return 0;
}
}
but this isn't an option for me because component is created after datasource (I have liquibase setup so it's too late) and Phase is still the same that means FIFO order and I'd like to be FILO.

Mix #Profile and #Component seams to me a bad idea. Profiles are designed to work with Configuration (documentation)
Do you really need profile? In my opinion it makes sense if you have several possible configurations, one based on H2, and if you want be able to switch between these configurations (typically at start time by setting a properties...)
Manage the H2 server with a bean (documentation) seams correct to me (as suggested by Stefen). Maybe you will prefer annotations... If you want a spring profile, then you will need a Configuration object too. It will simply load the H2 server bean (in my opinion it's better to manage the H2 server lifecycle with a bean than with a context/config).

Create your server as a bean :
#Bean(initMethod = "start", destroyMethod = "stop")
Server h2Server() throws Exception {
return Server.createTcpServer("-tcp","-tcpAllowOthers","-tcpPort","9192");
}
Now you can configure spring to create other beans (e.g the datasource)
after the bean h2Server using #DependsOn
#DependsOn("h2Server")
#Bean
DataSource dataSource(){
...
}
Hi, what about using spring boot? It has automatically configured datasource so I don't want to reconfigure it.
You are right, to use the above approach you have to create your own datasource in order to annotate it with #DependsOn .
But it looks like this is not really necessary.
In one of my projects I am creating the h2Server as a bean as described.
I use the datasource created by spring, so without any #DependsOn.
It works perfectly. Just give it a try.
Your solution with SmartLifecycle does not work, because it creates the server on ApplicationContext refresh, which happens after all beans (including the datasource ) were created.

Updating Dropwizard config at runtime

Is it possible to have my app update the config settings at runtime? I can easily expose the settings I want in my UI but is there a way to allow the user to update settings and make them permanent ie save them to the config.yaml file? The only way I can see it to update the file by hand then restart the server which seems a bit limiting.

Yes. It is possible to reload the service classes at runtime.
Dropwizard by itself does not have the way to reload the app, but jersey has.
Jersey uses a container object internally to maintain the running application. Dropwizard uses the ServletContainer class of Jersey to run the application.
How to reload the app without restarting it -
Get a handle to the container used internally by jersey
You can do this by registering a AbstractContainerLifeCycleListener in Dropwizard Environment before starting the app. and implement its onStartup method as below -
In your main method where you start the app -
//getting the container instance
environment.jersey().register(new AbstractContainerLifecycleListener() {
#Override
public void onStartup(Container container) {
//initializing container - which will be used to reload the app
_container = container;
}
});
Add a method to your app to reload the app. It will take in the list of string which are the names of the service classes you want to reload. This method will call the reload method of the container with the new custom DropWizardConfiguration instance.
In your Application class
public static synchronized void reloadApp(List<String> reloadClasses) {
DropwizardResourceConfig dropwizardResourceConfig = new DropwizardResourceConfig();
for (String className : reloadClasses) {
try {
Class<?> serviceClass = Class.forName(className);
dropwizardResourceConfig.registerClasses(serviceClass);
System.out.printf(" + loaded class %s.\n", className);
} catch (ClassNotFoundException ex) {
System.out.printf(" ! class %s not found.\n", className);
}
}
_container.reload(dropwizardResourceConfig);
}
For more details see the example documentation of jersey - jersey example for reload
Consider going through the code and documentation of following files in Dropwizard/Jersey for a better understanding -
Container.java
ContainerLifeCycleListener.java
ServletContainer.java
AbstractContainerLifeCycleListener.java
DropWizardResourceConfig.java
ResourceConfig.java

No.
Yaml file is parsed at startup and given to the application as Configuration object once and for all. I believe you can change the file after that but it wouldn't affect your application until you restart it.
Possible follow up question: Can one restart the service programmatically?
AFAIK, no. I've researched and read the code somewhat for that but couldn't find a way to do that yet. If there is, I'd love to hear that :).

I made a task that reloads the main yaml file (it would be useful if something in the file changes). However, it is not reloading the environment. After researching this, Dropwizard uses a lot of final variables and it's quite hard to reload these on the go, without restarting the app.
class ReloadYAMLTask extends Task {
private String yamlFileName;
ReloadYAMLTask(String yamlFileName) {
super("reloadYaml");
this.yamlFileName = yamlFileName;
}
#Override
public void execute(ImmutableMultimap<String, String> parameters, PrintWriter output) throws Exception {
if (yamlFileName != null) {
ConfigurationFactoryFactory configurationFactoryFactory = new DefaultConfigurationFactoryFactory<ReportingServiceConfiguration>();
ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
Validator validator = validatorFactory.getValidator();
ObjectMapper objectMapper = Jackson.newObjectMapper();
final ConfigurationFactory<ServiceConfiguration> configurationFactory = configurationFactoryFactory.create(ServiceConfiguration.class, validator, objectMapper, "dw");
File confFile = new File(yamlFileName);
configurationFactory.build(new File(confFile.toURI()));
}
}
}

You can change the configuration in the YAML and read it while your application is running. This will not however restart the server or change any server configurations. You will be able to read any changed custom configurations and use them. For example, you can change the logging level at runtime or reload other custom settings.
My solution -
Define a custom server command. You should use this command to start your application instead of the "server" command.
ArgsServerCommand.java
public class ArgsServerCommand<WC extends WebConfiguration> extends EnvironmentCommand<WC> {
private static final Logger LOGGER = LoggerFactory.getLogger(ArgsServerCommand.class);
private final Class<WC> configurationClass;
private Namespace _namespace;
public static String COMMAND_NAME = "args-server";
public ArgsServerCommand(Application<WC> application) {
super(application, "args-server", "Runs the Dropwizard application as an HTTP server specific to my settings");
this.configurationClass = application.getConfigurationClass();
}
/*
* Since we don't subclass ServerCommand, we need a concrete reference to the configuration
* class.
*/
#Override
protected Class<WC> getConfigurationClass() {
return configurationClass;
}
public Namespace getNamespace() {
return _namespace;
}
#Override
protected void run(Environment environment, Namespace namespace, WC configuration) throws Exception {
_namespace = namespace;
final Server server = configuration.getServerFactory().build(environment);
try {
server.addLifeCycleListener(new LifeCycleListener());
cleanupAsynchronously();
server.start();
} catch (Exception e) {
LOGGER.error("Unable to start server, shutting down", e);
server.stop();
cleanup();
throw e;
}
}
private class LifeCycleListener extends AbstractLifeCycle.AbstractLifeCycleListener {
#Override
public void lifeCycleStopped(LifeCycle event) {
cleanup();
}
}
}
Method to reload in your Application -
_ymlFilePath = null; //class variable
public static boolean reloadConfiguration() throws IOException, ConfigurationException {
boolean reloaded = false;
if (_ymlFilePath == null) {
List<Command> commands = _configurationBootstrap.getCommands();
for (Command command : commands) {
String commandName = command.getName();
if (commandName.equals(ArgsServerCommand.COMMAND_NAME)) {
Namespace namespace = ((ArgsServerCommand) command).getNamespace();
if (namespace != null) {
_ymlFilePath = namespace.getString("file");
}
}
}
}
ConfigurationFactoryFactory configurationFactoryFactory = _configurationBootstrap.getConfigurationFactoryFactory();
ValidatorFactory validatorFactory = _configurationBootstrap.getValidatorFactory();
Validator validator = validatorFactory.getValidator();
ObjectMapper objectMapper = _configurationBootstrap.getObjectMapper();
ConfigurationSourceProvider provider = _configurationBootstrap.getConfigurationSourceProvider();
final ConfigurationFactory<CustomWebConfiguration> configurationFactory = configurationFactoryFactory.create(CustomWebConfiguration.class, validator, objectMapper, "dw");
if (_ymlFilePath != null) {
// Refresh logging level.
CustomWebConfiguration webConfiguration = configurationFactory.build(provider, _ymlFilePath);
LoggingFactory loggingFactory = webConfiguration.getLoggingFactory();
loggingFactory.configure(_configurationBootstrap.getMetricRegistry(), _configurationBootstrap.getApplication().getName());
// Get my defined custom settings
CustomSettings customSettings = webConfiguration.getCustomSettings();
reloaded = true;
}
return reloaded;
}

Although this feature isn't supported out of the box by dropwizard, you're able to accomplish this fairly easy with the tools they give you.
Before I get started, note that this isn't a complete solution for the question asked as it doesn't persist the updated config values to the config.yml. However, this would be easy enough to implement yourself simply by writing to the config file from the application. If anyone would like to write this implementation feel free to open a PR on the example project I've linked below.
Code
Start off with a minimal config:
config.yml
myConfigValue: "hello"
And it's corresponding configuration file:
ExampleConfiguration.java
public class ExampleConfiguration extends Configuration {
private String myConfigValue;
public String getMyConfigValue() {
return myConfigValue;
}
public void setMyConfigValue(String value) {
myConfigValue = value;
}
}
Then create a task which updates the config:
UpdateConfigTask.java
public class UpdateConfigTask extends Task {
ExampleConfiguration config;
public UpdateConfigTask(ExampleConfiguration config) {
super("updateconfig");
this.config = config;
}
#Override
public void execute(Map<String, List<String>> parameters, PrintWriter output) {
config.setMyConfigValue("goodbye");
}
}
Also for demonstration purposes, create a resource which allows you to get the config value:
ConfigResource.java
#Path("/config")
public class ConfigResource {
private final ExampleConfiguration config;
public ConfigResource(ExampleConfiguration config) {
this.config = config;
}
#GET
public Response handleGet() {
return Response.ok().entity(config.getMyConfigValue()).build();
}
}
Finally wire everything up in your application:
ExampleApplication.java (exerpt)
environment.jersey().register(new ConfigResource(configuration));
environment.admin().addTask(new UpdateConfigTask(configuration));
Usage
Start up the application then run:
$ curl 'http://localhost:8080/config'
hello
$ curl -X POST 'http://localhost:8081/tasks/updateconfig'
$ curl 'http://localhost:8080/config'
goodbye
How it works
This works simply by passing the same reference to the constructor of ConfigResource.java and UpdateConfigTask.java. If you aren't familiar with the concept see here:
Is Java "pass-by-reference" or "pass-by-value"?
The linked classes above are to a project I've created which demonstrates this as a complete solution. Here's a link to the project:
scottg489/dropwizard-runtime-config-example
Footnote: I haven't verified this works with the built in configuration. However, the dropwizard Configuration class which you need to extend for your own configuration does have various "setters" for internal configuration, but it may not be safe to update those outside of run().
Disclaimer: The project I've linked here was created by me.