Arez-Persist

This library provides annotation driven infrastructure for persisting observable properties on Arez components. The library has built-in support for storing properties in memory, within a browser session or across browser sessions but allows users to supply their own mechanisms for persisting state.

Quick Start

The simplest way to use the library;

• add the following dependencies into the build system. i.e.

<dependency>
   <groupId>org.realityforge.arez.persist</groupId>
   <artifactId>arez-persist-core</artifactId>
   <version>0.46</version>
</dependency>

• To enable the annotation processor used by the framework, you need add the following snippet to configure the maven compiler plugin from within the pom.xml:

<project>
  ...
  <plugins>
    ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.5.1</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
          <useIncrementalCompilation>false</useIncrementalCompilation>
          <annotationProcessorPaths>
            <path>
               <groupId>org.realityforge.arez.persist</groupId>
               <artifactId>arez-persist-processor</artifactId>
               <version>0.46</version>
            </path>
          </annotationProcessorPaths>
        </configuration>
      </plugin>
      ...
    </plugins>
  </build>
</project>

• If you are using ArezPersist within a GWT application you will also need to inherit the appropriate GWT module in your .gwt.xml file. It is usually sufficient to add:

<module>
  ...
  <inherits name='arez.persist.Persist'/>
  ...
</module>

If you want the framework to perform validation and invariant checking you can instead inherit the Dev module instead. The Dev module is very useful during development as it adds a level of safety and error checking, but it should not be used in production environments as it adds some overhead in terms of code size and execution speed. The Dev module can be added via:

<module>
  ...
  <inherits name='arez.persist.PersistDev'/>
  ...
</module>

• Configure the stores used to persist component state. There are 3 types of store included in the library. One store is purely in memory and is lost on application reload, one persists to the browser's session storage and thus will be restored even when the tab is reloaded and the last is stored in the browser's local storage and is persisted even after the tab is closed.

  The in-memory store is automatically created unless disable at compile time. (See the compile-time settings in the Persist.gwt.xml module). While the other two stores must be explicitly created via:

// register a "session" store using the browsers session storage. Store state under
// the "myapp" key in the session storage.
ArezPersistBrowserUtil.registerSessionStore( "myapp" );

// register a "local" store using the browsers local storage. Store state under
// the "myapp" key in the local storage.
ArezPersistBrowserUtil.registerLocalStore( "myapp" );

• Explicitly register converters for any types that may need them. The converters are responsible for encoding values in a form compatible with the stores. The actual converters needed will depend on the types of the properties marked with the @Persist annotation and the requirements of the store.

  This library is expected to be used within a browser context where all non-double values are represented as doubles when stored as json objects which is how the inbuilt local and session stores persist state. As such, the library defines several converters that can be registered by invoking methods on the ArezPersistBrowserUtil class. If these converters are not used then they should not be registered as each converter adds some overhead. However, the converters useful in a browser may be registered via:

ArezPersistBrowserUtil.registerCharacterConverter();
ArezPersistBrowserUtil.registerByteConverter();
ArezPersistBrowserUtil.registerShortConverter();
ArezPersistBrowserUtil.registerIntegerConverter();
ArezPersistBrowserUtil.registerLongConverter();
ArezPersistBrowserUtil.registerFloatConverter();

A developer can also register custom converters via:

ArezPersist.registerConverter( SomeType.class, new SomeTypeConverter() );

• Next, the arez component that you want to persist the state of must be annotated with the @PersistType annotation. The state of an @Observable annotated property can be persisted by annotating the getter with @Persist. The store used to persist the proeprty can be specified as a parameter on the @Persist annotation. See the javadocs for the @Persist and @PersistType annotations for further details.

  It should be noted that the @ArezComponent.requireId and @ArezComponent.disposeNotifier parameters must resolve to ENABLE for ArezPersist to work but the annotation processor will not yet generate errors if this is not the case. The arez component should also have a string component id or one maps to a string in stable manner.

@PersistType
@ArezComponent( requireId = Feature.ENABLE, disposeNotifier = Feature.ENABLE )
public abstract class TreeNode
{
  ...
  // Store the "expanded" flag for tree node in local storage
  @Persist( store = StoreTypes.LOCAL )
  @Observable
  public abstract boolean isExpanded();

  public abstract void setExpanded( boolean expanded );
  ...
}

More Information

For more information about component, please see the Website. For the source code and project support please visit the GitHub project.

Contributing

The component was released as open source so others could benefit from the project. We are thankful for any contributions from the community. A Code of Conduct has been put in place and a Contributing document is under development.

License

The component is licensed under Apache License, Version 2.0.

Credit

• Stock Software for providing significant support in building and maintaining Arez-Persist.