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This directory contains two reusable Metadata Adapters, called FileBasedProvider and LiteralBasedProvider.
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README.md

Lightstreamer - Reusable Metadata Adapters - Java Adapter

This project includes two simple full implementations of Metadata Adapter in Java made available as sample for inspiration and/or extension.

LiteralBasedProvider Metadata Adapter

The LiteralBasedProvider extends the MetadataProviderAdapter abstract class (which in turn implements the MetadataProvider interface). It is used in many Lightstreamer examples and demos, in combination with different Data Adapters and Clients. It is also useful when developing proof of concepts and prototypes, where the main focus is on the Data Adapter. Its binaries are included in the Server distribution.

FileBasedProvider Metadata Adapter

The FileBasedProvider extends the LiteralBasedProvider, but is rarely used.



Build

Before you can compile the adapters, some dependencies need to be solved:

  • Get the ls-adapter-interface.jar file from the Lightstreamer 6 distribution, you can find it in the Lightstreamer/DOCS-SDKs/sdk_adapter_java_inprocess/lib folder, and put it in a temporary folder, let's call it compile_libs.

Note that ls-adapter-interface.jar already includes the class files for com.lightstreamer.adapters.metadata.LiteralBasedProvider; we can ignore that for a moment. If you are testing your own modified version of the LiteralBasedProvider code, take care of changing the package name, or, at least, the class name.

Now you can generate the jar for the sample Metadata Adapters, let's call it ls-generic-adapters.jar, with the following commands:

  >mkdir tmp_classes

  >javac -source 1.7 -target 1.7 -nowarn -g -classpath compile_libs/ls-adapter-interface.jar -sourcepath src -d tmp_classes src/com/lightstreamer/adapters/metadata/LiteralBasedProvider.java src/com/lightstreamer/adapters/metadata/FileBasedProvider.java

  >jar cvf ls-generic-adapters.jar -C tmp_classes com/lightstreamer

Deploy

To use one of the Metadata Adapters just built in some adapter set, just copy the ls-generic-adapters.jar file to the lib directory of the Adapter Set installation. To use these Metadata Adapters in multiple Adapter Sets, you may also copy the ls-generic-adapters.jar file in the shared/lib directory of your Lightstreamer Server installation. As said, the class files for com.lightstreamer.adapters.metadata.LiteralBasedProvider are already included in ls-adapter-interface.jar, which is part of Lightstreamer Server installation; hence this step is not needed for the LiteralBasedProvider.

Then configure the right Metadata provider and its properties in the adapters.xml descriptor file within your adapters' subfolder. The following code snippet shows an example:

  <!-- Mandatory. Define the Metadata Provider. -->
  <metadata_provider>
    <!-- Mandatory. Java class name of the adapter. -->
    <adapter_class>com.lightstreamer.adapters.metadata.LiteralBasedProvider</adapter_class>

    <!-- Optional. List of initialization parameters specific for the adapter. -->

    <!-- Optional (specific for adapters that inherit from
             com.lightstreamer.adapters.metadata.FileBasedProvider).
             search_dir: path of the directory containing all *.items and
             *.schema files, relative to the config directory.
             static: define whether to cache the files or refresh them any time
             they are needed.
             See the FileBasedProvider javadoc. -->
     <!--
    <param name="search_dir">.</param>
    <param name="static">Y</param>
     -->
    <!-- Optional (specific for adapters that inherit from
             com.lightstreamer.adapters.metadata.FileBasedProvider or
             com.lightstreamer.adapters.metadata.LiteralBasedProvider).
             Define values to be returned in getAllowedMaxBandwidth(),
             getAllowedMaxItemFrequency(), getAllowedBufferSize() and
             getDistinctSnapshotLength() methods, for any User and Item
             supplied and optional comma-separated list of User names
             to be allowed by the notifyUser() method.
             See LiteralBasedProvider javadoc. -->
     <!--
    <param name="max_bandwidth">40</param>
    <param name="max_frequency">3</param>
    <param name="buffer_size">30</param>
    <param name="distinct_snapshot_length">10</param>
    <param name="allowed_users">user123,user456</param>
     -->
     <!-- Optional (specific for adapters that inherit from
             com.lightstreamer.adapters.metadata.FileBasedProvider or
             com.lightstreamer.adapters.metadata.LiteralBasedProvider).
             Define how the modeMayBeAllowed method should behave, by
             associating to each item the modes in which it can be managed
             by the Server.
             Each pair of parameters of the form "item_family_<n>" and
             "modes_for_item_family_<n>" define respectively the item name
             pattern (in java.util.regex.Pattern format) and the allowed
             modes (in comma separated format) for a family of items.
             Each item is assigned to the first family that matches its name.
             If no families are specified at all, then modeMayBeAllowed
             always returns true, though this is not recommended, because
             the Server does not support more than one mode out of MERGE,
             DISTINCT, and COMMAND for the same item. In such a case, the
             Server would just manage each item in the mode specified by the
             first Client request it receives for the item and would be up to
             the Clients to ensure that the same item cannot be requested in
             two conflicting Modes.
             See LiteralBasedProvider javadoc. -->
    <param name="item_family_1">item.*</param>
    <param name="modes_for_item_family_1">MERGE</param>
    <!--
    <param name="item_family_2">item.*</param>
    <param name="modes_for_item_family_2">MERGE,RAW</param>
     -->
  </metadata_provider>

Above, are shown only the specific parameters of LiteralBasedProvider Metadata Adapter. Use the generic template, DOCS-SDKs/sdk_adapter_java_inprocess/doc/adapter_conf_template/adapters.xml, as a reference for a complete overview of configuration options.

See Also

Lightstreamer Compatibility Notes

  • Compatible with Lightstreamer SDK for Java In-Process Adapters since 6.0
  • For a version of this example compatible with Lightstreamer SDK for Java Adapters version 5.1, please refer to this tag.
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