Posts by Hubert Klein Ikkink

Groovy Goodness: Use Expanded Variables in SQL GString Query

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Hubert Klein Ikkink

Working with SQL database from Groovy code is very easy using the groovy.sql.Sql class. The class has several methods to execute a SQL query, but we have to take special care if we use methods from Sql that take a GString argument. Groovy will extract all variable expressions and use them as values for placeholders in a PreparedStatement constructed from the SQL query. If we have variable expressions that should not be extracted as parameters for a PreparedStatement we must use the Sql.expand method. This method will make the variable expression a groovy.sql.ExpandedVariable object. This object is not used as parameter for a PreparedStatement query, but the value is evaluated as GString variable expression.

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Spicy Spring: Group Loggers With Logical Name

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Hubert Klein Ikkink

Spring Boot 2.1 introduced log groups. A log group is a logical name for one or more loggers. We can define log groups in our application configuration. Then we can set the log level for a group, so all loggers in the group will get the same log level. This can be very useful to change a log level for multiple loggers that belong together with one setting. Spring Boot already provides two log groups by default: web and sql. In the following list we see which loggers are part of the default log groups:

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Awesome Asciidoctor: Exclude Parts From Included Files

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Hubert Klein Ikkink

In a previous post we learned how to include parts of a document in the generated output. The included parts are defined using tags. The start of a tag is defined in a comment with the format tag::_tagName_[] and the end has the format end::_tagName_[]. Next we must use the tags attribute for the include macro followed by the tagName. If we don’t want to include a tag we must prefix it with an exclamation mark (!).

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Gradle Goodness: Generate Javadoc In HTML5

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Hubert Klein Ikkink

Since Java 9 we can specify that the Javadoc output must be generated in HTML 5 instead of the default HTML 4. We need to pass the option -html5 to the javadoc tool. To do this in Gradle we must add the option to the javadoc task configuration. We use the addBooleanOption method of the options property that is part of the javadoc task. We set the argument to html5 and the value to true.

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Gradle Goodness: Rerun Incremental Tasks At Specific Intervals

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Hubert Klein Ikkink

One of the most important features in Gradle is the support for incremental tasks. Incremental tasks have input and output properties that can be checked by Gradle. When the values of the properties haven’t changed then the task can be marked as up to date by Gradle and it is not executed. This makes a build much faster. Input and output properties can be files, directories or plain object values. We can set a task input property with a date or date/time value to define when a task is up to date for a specific period. As long as the value of the input property hasn’t changed (and of course also the other input and output property values) Gradle will not rerun task and mark it as up to date. This is useful for example if a long running task (e.g. large integration test suite) only needs to run once a day or another period.

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Micronaut Mastery: Configuration Property Name Is Lowercased And Hyphen Separated

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Hubert Klein Ikkink

In Micronaut we can inject configuration properties in different ways into our beans. We can use for example the @Value annotation using a string value with a placeholder for the configuration property name. If we don’t want to use a placeholder we can also use the @Property annotation and set the name attribute to the configuration property name. We have to pay attention to the format of the configuration property name we use. If we refer to a configuration property name using @Value or @Property we must use lowercased and hyphen separated names (also known as kebab casing). Even if the name of the configuration property is camel cased in the configuration file. For example if we have a configuration property sample.theAnswer in our application.properties file, we must use the name sample.the-answer to get the value.

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Micronaut Mastery: Consuming Server-Sent Events (SSE)

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Hubert Klein Ikkink

Normally we would consume server-sent events (SSE) in a web browser, but we can also consume them in our code on the server. Micronaut has a low-level HTTP client with a SseClient interface that we can use to get server-sent events. The interface has an eventStream method with different arguments that return a Publisher type of the Reactive Streams API. We can use the RxSseClient interface to get back RxJava2 Flowable return type instead of Publisher type. We can also use Micronaut’s declarative HTTP client, which we define using the @Client annotation, that supports server-sent events with the correct annotation attributes.

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Micronaut Mastery: Use Micronaut Beans In Spring Applications

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Hubert Klein Ikkink

We can add Micronaut beans to the application context of a Spring application. Micronaut has a MicronautBeanProcessor class that we need to register as Spring bean in the Spring application context. We can define which Micronaut bean types need to be added to the Spring application context via the constructor of the MicronautBeanProcessor class. This way we can use Micronaut from inside a Spring application. For example we can use the declarative HTTP client of Micronaut in our Spring applications.

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Micronaut Mastery: Running Code On Startup

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Hubert Klein Ikkink

When our Micronaut application starts we can listen for the ServiceStartedEvent event and write code that needs to run when the event is fired. We can write a bean that implements the ApplicationEventListener interface with the type ServiceStartedEvent. Or we can use the @EventListener annotation on our method with code we want to run on startup. If the execution of the code can take a while we can also add the @Async annotation to the method, so Micronaut can execute the code on a separate thread.

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Spicy Spring: Dockerize Spring Boot Application With Jib

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Hubert Klein Ikkink

Jib is an open-source Java library from Google for creating Docker images for Java applications. Jib can be used as Maven or Gradle plugin in our Spring Boot project. One of the nice feature of Jib is that it adds layers with our classes, resources and dependency libraries for the Docker image. This means that when only class files have changed, the classes layer is rebuild, but the others remain the same. Therefore the creation of a Docker image with our Spring Boot application is also very fast (after the first creation). Also the Maven and Gradle plugins have sensible defaults, like using the project name and version as image name, so we don’t have to configure anything in our build tool. Although Jib provides options to configure other values for the defaults, for example to change the JVM options passed on to the application.

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Awesome Asciidoctor: Document Attributes With Styling

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Hubert Klein Ikkink

Document attributes in Asciidoctor are very powerful. We can assign values to a document attributes and reference the attribute name in our document enclosed between curly braces. Asciidoctor will fill in the value when the document is transformed. Instead of a plain value we can also use styling markup in the document attribute definition. We must use the passthrough macro and allow for quote substitution.

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