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# Configuration Management
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Centralized configuration system with hierarchical property management, secure configuration handling, and comprehensive constants for all CDAP settings.
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## Capabilities
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### Core Configuration Classes
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Main configuration classes for managing CDAP settings and properties.
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```java { .api }
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/**
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 * Main configuration class for CDAP
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 */
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public class CConfiguration extends Configuration {
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    public static CConfiguration create();
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    public static CConfiguration create(Configuration baseConf);
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    public String get(String name);
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    public String get(String name, String defaultValue);
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    public int getInt(String name, int defaultValue);
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    public long getLong(String name, long defaultValue);
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    public boolean getBoolean(String name, boolean defaultValue);
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    public void set(String name, String value);
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    public void setInt(String name, int value);
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    public void setLong(String name, long value);
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    public void setBoolean(String name, boolean value);
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}
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/**
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 * Secure configuration management for sensitive data
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 */
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public class SConfiguration extends Configuration {
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    public static SConfiguration create();
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    public static SConfiguration create(Configuration baseConf);
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    public String get(String name);
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    public String get(String name, String defaultValue);
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    public void set(String name, String value);
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}
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```
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**Usage Examples:**
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```java
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import io.cdap.cdap.common.conf.CConfiguration;
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import io.cdap.cdap.common.conf.SConfiguration;
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// Create and use CConfiguration
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CConfiguration cConf = CConfiguration.create();
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// Read configuration values
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String appFabricHost = cConf.get(Constants.AppFabric.SERVER_ADDRESS, "localhost");
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int appFabricPort = cConf.getInt(Constants.AppFabric.SERVER_PORT, 11015);
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boolean sslEnabled = cConf.getBoolean(Constants.Security.SSL.EXTERNAL_ENABLED, false);
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// Set configuration values
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cConf.set("custom.property", "custom-value");
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cConf.setInt("custom.port", 8080);
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// Secure configuration for sensitive data
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SConfiguration sConf = SConfiguration.create();
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sConf.set("database.password", "secret-password");
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String dbPassword = sConf.get("database.password");
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```
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### Configuration Constants
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Central location for all CDAP configuration constants organized by functional area.
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```java { .api }
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/**
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 * Central location for all CDAP configuration constants
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 */
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public final class Constants {
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    /**
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     * Service names and configurations
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     */
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    public static final class Service {
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        public static final String MASTER_SERVICES = "master.services";
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        public static final String APP_FABRIC_HTTP = "app.fabric.http";
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        public static final String DATASET_MANAGER = "dataset.service";
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        public static final String METRICS = "metrics";
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        public static final String METRICS_PROCESSOR = "metrics.processor";
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        public static final String LOGSAVER = "log.saver";
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        public static final String TRANSACTION = "transaction";
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        public static final String STREAMS = "streams";
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    }
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    /**
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     * Security-related constants
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     */
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    public static final class Security {
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        public static final String ENABLED = "security.enabled";
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        public static final String AUTHORIZATION_ENABLED = "security.authorization.enabled";
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        public static final class SSL {
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            public static final String EXTERNAL_ENABLED = "security.server.ssl.enabled";
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            public static final String EXTERNAL_KEYSTORE_PATH = "security.server.ssl.keystore.path";
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            public static final String EXTERNAL_KEYSTORE_PASSWORD = "security.server.ssl.keystore.password";
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            public static final String EXTERNAL_KEYSTORE_TYPE = "security.server.ssl.keystore.type";
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        }
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        public static final class Authentication {
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            public static final String HANDLERCLASSNAME = "security.authentication.handlerClassName";
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            public static final String LOGINMODULE = "security.authentication.loginmodule.className";
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        }
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        public static final class Authorization {
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            public static final String EXTENSION_JAR_PATH = "security.authorization.extension.jar.path";
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            public static final String EXTENSION_EXTRA_CLASSPATH = "security.authorization.extension.extra.classpath";
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        }
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    }
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    /**
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     * Metrics configuration constants
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     */
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    public static final class Metrics {
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        public static final String ADDRESS = "metrics.bind.address";
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        public static final String PORT = "metrics.bind.port";
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        public static final String RETENTION_SECONDS = "metrics.retention.seconds";
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        public static final String NUM_INSTANCES = "metrics.num.instances";
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        public static final String NUM_CORES = "metrics.num.cores";
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        public static final String MEMORY_MB = "metrics.memory.mb";
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    }
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    /**
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     * Dataset-related constants  
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     */
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    public static final class Dataset {
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        public static final String MANAGER_ADDRESS = "dataset.service.bind.address";
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        public static final String MANAGER_PORT = "dataset.service.bind.port";
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        public static final String EXECUTOR_ADDRESS = "dataset.executor.bind.address";
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        public static final String EXECUTOR_PORT = "dataset.executor.bind.port";
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    }
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    /**
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     * API versioning constants
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     */
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    public static final class Gateway {
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        public static final String API_VERSION_3_TOKEN = "v3";
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        public static final String API_VERSION_3 = "/" + API_VERSION_3_TOKEN;
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        public static final String INTERNAL_API_VERSION_3_TOKEN = "v3Internal";
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        public static final String INTERNAL_API_VERSION_3 = "/" + INTERNAL_API_VERSION_3_TOKEN;
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    }
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    /**
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     * Router configuration
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     */
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    public static final class Router {
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        public static final String ADDRESS = "router.bind.address";
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        public static final String BIND_PORT = "router.bind.port";
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        public static final String SERVER_BOSS_THREADS = "router.server.boss.threads";
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        public static final String SERVER_WORKER_THREADS = "router.server.worker.threads";
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    }
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    /**
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     * Logging configuration
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     */
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    public static final class Logging {
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        public static final String COMPONENT_NAME = "component.name";
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        public static final String KAFKA_TOPIC = "kafka.topic";
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    }
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    /**
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     * Messaging system configuration
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     */
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    public static final class MessagingSystem {
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        public static final String HTTP_SERVER_BIND_ADDRESS = "messaging.bind.address";
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        public static final String HTTP_SERVER_BIND_PORT = "messaging.bind.port";
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        public static final String CONTAINER_VIRTUAL_CORES = "messaging.container.virtual.cores";
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        public static final String CONTAINER_MEMORY_MB = "messaging.container.memory.mb";
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    }
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}
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```
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### Configuration Interfaces
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Base interfaces for configuration management and property storage.
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```java { .api }
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/**
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 * Base configuration interface
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 */
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public interface Configuration {
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    String get(String name);
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    String get(String name, String defaultValue);
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    void set(String name, String value);
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    Iterable<Map.Entry<String, String>> iterator();
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}
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/**
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 * Interface for configurable components
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 */
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public interface Configurable {
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    void configure(Configuration conf);
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}
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/**
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 * Property storage abstraction
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 */
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public interface PropertyStore<T> {
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    T get(String key);
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    void put(String key, T value);
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    void remove(String key);
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    boolean exists(String key);
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}
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/**
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 * Interface for property change notifications
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 */
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public interface PropertyChangeListener {
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    void onPropertyChange(String key, String oldValue, String newValue);
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}
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```
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**Advanced Usage Examples:**
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```java
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import io.cdap.cdap.common.conf.*;
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// ZooKeeper configuration helper
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public class ZooKeeperConfig {
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    public static String getZkQuorum(CConfiguration cConf) {
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        return Constants.Zookeeper.getZkQuorum(cConf);
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    }
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    public static String getZkNamespace(CConfiguration cConf) {
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        return cConf.get(Constants.Zookeeper.CFG_SESSION_TIMEOUT_MILLIS, "default");
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    }
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}
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// Custom configurable component
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public class MyService implements Configurable {
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    private String bindAddress;
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    private int bindPort;
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    @Override
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    public void configure(Configuration conf) {
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        this.bindAddress = conf.get("my.service.bind.address", "localhost");
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        this.bindPort = conf.getInt("my.service.bind.port", 8080);
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    }
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    public void start() {
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        // Start service with configured address and port
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        System.out.println("Starting service on " + bindAddress + ":" + bindPort);
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    }
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}
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// Property change monitoring
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public class ConfigMonitor implements PropertyChangeListener {
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    @Override
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    public void onPropertyChange(String key, String oldValue, String newValue) {
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        System.out.println("Configuration changed: " + key + " = " + newValue);
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        // React to specific configuration changes
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        if (Constants.Security.ENABLED.equals(key)) {
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            // Reconfigure security settings
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            reconfigureSecurity(Boolean.parseBoolean(newValue));
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        }
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    }
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    private void reconfigureSecurity(boolean enabled) {
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        // Update security configuration
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    }
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}
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// Using property store
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public class ConfigCache {
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    private final PropertyStore<String> cache;
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    public ConfigCache(PropertyStore<String> cache) {
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        this.cache = cache;
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    }
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    public String getCachedProperty(String key, CConfiguration cConf) {
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        if (cache.exists(key)) {
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            return cache.get(key);
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        }
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        String value = cConf.get(key);
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        cache.put(key, value);
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        return value;
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    }
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}
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```