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# Client Management
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Core client functionality for connecting to Flink clusters, managing configuration, and handling client lifecycle operations.
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## Capabilities
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### Client Creation
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Create a QueryableStateClient to connect to a Flink cluster's client proxy.
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```java { .api }
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public QueryableStateClient(String remoteHostname, int remotePort) throws UnknownHostException;
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public QueryableStateClient(InetAddress remoteAddress, int remotePort);
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```
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**Parameters:**
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- `remoteHostname` - Hostname of the client proxy to connect to (throws UnknownHostException if invalid)
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- `remotePort` - Port of the client proxy (must be in range 0-65535)
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- `remoteAddress` - InetAddress of the client proxy to connect to
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**Usage Example:**
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```java
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// Connect using hostname
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QueryableStateClient client = new QueryableStateClient("localhost", 9069);
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// Connect using InetAddress
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InetAddress address = InetAddress.getByName("192.168.1.100");
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QueryableStateClient client = new QueryableStateClient(address, 9069);
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```
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### Configuration Management
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Configure execution settings and classloader for serialization.
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```java { .api }
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public ExecutionConfig getExecutionConfig();
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public ExecutionConfig setExecutionConfig(ExecutionConfig config);
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public ClassLoader setUserClassLoader(ClassLoader userClassLoader);
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```
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**Returns:**
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- `getExecutionConfig()` - Current ExecutionConfig or null if not set
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- `setExecutionConfig()` - Previous ExecutionConfig or null if none was set
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- `setUserClassLoader()` - Previous ClassLoader or null if none was set
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**Usage Example:**
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```java
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QueryableStateClient client = new QueryableStateClient("localhost", 9069);
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// Configure execution config
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ExecutionConfig config = new ExecutionConfig();
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config.enableObjectReuse(); // Example configuration
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ExecutionConfig previous = client.setExecutionConfig(config);
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// Set custom classloader for serialization
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ClassLoader customClassLoader = Thread.currentThread().getContextClassLoader();
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client.setUserClassLoader(customClassLoader);
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```
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### Lifecycle Management
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Manage the client lifecycle with proper shutdown procedures.
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```java { .api }
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public CompletableFuture<?> shutdownAndHandle();
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public void shutdownAndWait();
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```
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**Returns:**
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- `shutdownAndHandle()` - CompletableFuture that completes when shutdown is finished
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- `shutdownAndWait()` - void (blocks until shutdown completes)
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**Behavior:**
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- `shutdownAndHandle()` - Returns a future for asynchronous shutdown handling
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- `shutdownAndWait()` - Blocks the calling thread until shutdown completes; logs warnings on exceptions
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**Usage Example:**
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```java
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QueryableStateClient client = new QueryableStateClient("localhost", 9069);
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// Perform queries...
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// Asynchronous shutdown
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client.shutdownAndHandle().thenRun(() -> {
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    System.out.println("Client shutdown completed");
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}).exceptionally(throwable -> {
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    System.err.println("Shutdown failed: " + throwable.getMessage());
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    return null;
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});
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// Or synchronous shutdown
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client.shutdownAndWait();
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```
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## Internal Components
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The client internally manages:
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- **Network Client**: Netty-based client for communication with the cluster
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- **Message Serialization**: Handles KvStateRequest/KvStateResponse serialization
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- **Statistics**: Optional request statistics tracking (disabled by default)
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- **Remote Address**: Cached connection information for the client proxy
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The client proxy serves as the entry point to the Flink cluster, forwarding requests to the JobManager for location resolution and to TaskManagers for actual state queries.