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variable-replacers

README.md

Pluggable Variable Replacers

This code sample shows how to implement and use the pluggable configuration replacer feature introduced in Hazelcast 3.10.

Build and run the samples

Build this sample with Maven.

mvn clean install

There are several Maven profiles prepared to execute the samples in the pom.xml. Use following command to run them:

mvn exec:java -P [profileName]
Profile name Related XML file Description
show.encryption-help Executes the EncryptionReplacer without parameters. It just prints a help.
generate.encrypted-variable hazelcast-with-replacers.xml Executes the EncryptionReplacer with arguments provided. It encrypts the provided String with configuration loadad from the XML file. The resulting Variable is printed to standard output.
run.hazelcast-plain hazelcast-plain.xml Starts Hazelcast server without replacers used.
run.hazelcast-with-replacers hazelcast-with-replacers.xml Starts Hazelcast server with EncryptionReplacer and sample IdReplacer used in the configuration.
run.hazelcast-exec-linux hazelcast-exec-linux.xml Starts Hazelcast server with sample ExecReplacer used in the configuration. The command used (echo) should be available on most Unix/Linux-like systems.
run.hazelcast-exec-windows hazelcast-exec-windows.xml Starts Hazelcast server with sample ExecReplacer used in the configuration. The commands used (cmd.exe and its echo) should be available on Windows systems.

Background

The Variable Replacers are implementations of ConfigReplacer interface. They replaces placeholder strings called Variables in the Hazelcast and Hazelcast client XML configuration files.

The Strings are replaced during loading the configuration.

A Variable to be replaced within the configuration file has the following form:

"$" PREFIX "{" VALUE "}"

The PREFIX is a value returned by getPrefix() method and the VALUE is a value provided to the getReplacement(String) method. The result of ConfigReplacer.getReplacement(String) method call replaces the whole Variable string.

Sample ConfigReplacer implementations

IdReplacer
Full class name com.hazelcast.sample.replacer.IdReplacer
Replacer prefix Id

The IdReplacer A very simple variable replacer, which just returns provided value (i.e. identity function). It's easy to use it as a starting point for other custom ConfigReplacer implementations.

The IdReplacer has no configurable options.

ExecReplacer
Full class name com.hazelcast.sample.replacer.ExecReplacer
Replacer prefix EXEC

The ExecReplacer is a ready to use implementation, which runs external command and uses its standard output as the value for the variable.

Options

Option Mandatory Default value Description
argumentSeparator no "\s+" (whitespaces) A regular expression used as a separator betwen arguments. It can be used when command path or argument contains whitespaces.
requiresZeroExitCode no true A true/false flag which controls if a non-zero exit code is allowed to continue with the replacement.

Example

<hazelcast>
    <config-replacers>
        <replacer class-name="com.hazelcast.config.replacer.ExecReplacer">
            <properties>
                <property name="argumentSeparator">#</property>
            </properties>
        </replacer>
    </config-replacers>
    <group>
        <!-- read group name from "hazelcast group.txt" file -->
        <name>$EXEC{cat#/opt/hazelcast group.txt}</name>
    </group>
</hazelcast>