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# Apache Flink Twitter Connector
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Apache Flink Twitter connector provides streaming data ingestion from the Twitter API. It implements a RichSourceFunction that emits tweets as strings, using Twitter's Hosebird Client (HBC) library for reliable streaming connections with OAuth1 authentication and rate limiting support.
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## Package Information
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- **Package Name**: flink-connector-twitter_2.12
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- **Group ID**: org.apache.flink
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- **Package Type**: Maven
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- **Language**: Java
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- **Installation**: Add to Maven dependencies:
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```xml
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<dependency>
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    <groupId>org.apache.flink</groupId>
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    <artifactId>flink-connector-twitter_2.12</artifactId>
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    <version>1.14.6</version>
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</dependency>
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```
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## Core Imports
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```java
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import org.apache.flink.streaming.connectors.twitter.TwitterSource;
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import org.apache.flink.streaming.connectors.twitter.TwitterSource.EndpointInitializer;
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import org.apache.flink.streaming.api.functions.source.SourceFunction.SourceContext;
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import org.apache.flink.configuration.Configuration;
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import com.twitter.hbc.core.endpoint.StreamingEndpoint;
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import java.util.Properties;
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```
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## Basic Usage
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```java
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import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
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import org.apache.flink.streaming.connectors.twitter.TwitterSource;
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import java.util.Properties;
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// Configure Twitter credentials
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Properties props = new Properties();
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props.setProperty(TwitterSource.CONSUMER_KEY, "your-consumer-key");
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props.setProperty(TwitterSource.CONSUMER_SECRET, "your-consumer-secret");
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props.setProperty(TwitterSource.TOKEN, "your-access-token");
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props.setProperty(TwitterSource.TOKEN_SECRET, "your-access-token-secret");
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// Create and configure the source
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TwitterSource twitterSource = new TwitterSource(props);
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// Use in Flink streaming job
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StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
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env.addSource(twitterSource)
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   .print();
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env.execute("Twitter Stream Job");
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```
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## Advanced Usage Examples
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### Custom Endpoint with Error Handling
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```java
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import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
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import org.apache.flink.streaming.connectors.twitter.TwitterSource;
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import com.twitter.hbc.core.endpoint.StatusesFilterEndpoint;
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import java.util.Arrays;
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import java.util.Properties;
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try {
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    // Configure properties
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    Properties props = new Properties();
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    props.setProperty(TwitterSource.CONSUMER_KEY, "your-consumer-key");
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    props.setProperty(TwitterSource.CONSUMER_SECRET, "your-consumer-secret");
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    props.setProperty(TwitterSource.TOKEN, "your-access-token");
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    props.setProperty(TwitterSource.TOKEN_SECRET, "your-access-token-secret");
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    props.setProperty(TwitterSource.CLIENT_NAME, "my-flink-app");
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    props.setProperty(TwitterSource.CLIENT_BUFFER_SIZE, "100000");
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    // Create source with custom endpoint
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    TwitterSource twitterSource = new TwitterSource(props);
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    twitterSource.setCustomEndpointInitializer(() -> {
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        StatusesFilterEndpoint endpoint = new StatusesFilterEndpoint();
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        endpoint.trackTerms(Arrays.asList("apache", "flink", "bigdata"));
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        return endpoint;
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    });
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    // Setup streaming environment
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    StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
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    env.enableCheckpointing(10000); // Enable checkpointing for fault tolerance
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    env.addSource(twitterSource)
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       .filter(tweet -> tweet.contains("apache"))
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       .print();
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    env.execute("Filtered Twitter Stream");
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} catch (IllegalArgumentException e) {
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    System.err.println("Configuration error: " + e.getMessage());
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} catch (Exception e) {
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    System.err.println("Execution error: " + e.getMessage());
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}
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```
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### Resource Management Pattern
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```java
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import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
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import org.apache.flink.streaming.connectors.twitter.TwitterSource;
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public class TwitterStreamingJob {
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    public static void main(String[] args) throws Exception {
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        Properties props = loadTwitterProperties(); // Your property loading logic
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        TwitterSource twitterSource = new TwitterSource(props);
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        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
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        // Configure proper resource management
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        env.enableCheckpointing(5000);
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        env.setRestartStrategy(RestartStrategies.fixedDelayRestart(3, 10000));
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        env.addSource(twitterSource)
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           .name("Twitter Source")
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           .setParallelism(1) // TwitterSource is not parallelizable
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           .map(tweet -> processTweet(tweet))
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           .print();
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        env.execute("Robust Twitter Stream");
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    }
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    private static String processTweet(String rawTweet) {
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        // Your tweet processing logic
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        return rawTweet;
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    }
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}
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```
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## Capabilities
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### Twitter Source Creation
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Creates a Twitter streaming source with OAuth authentication and configurable properties. The TwitterSource extends RichSourceFunction<String> and implements Flink's SourceFunction interface.
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```java { .api }
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/**
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 * Creates a TwitterSource for streaming tweets from Twitter API
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 * @param properties Configuration properties containing OAuth credentials and optional settings
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 * @throws IllegalArgumentException if required properties are missing
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 */
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public class TwitterSource extends RichSourceFunction<String> {
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    public TwitterSource(Properties properties);
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}
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```
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**Required Properties:**
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- `twitter-source.consumerKey` - Twitter application consumer key
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- `twitter-source.consumerSecret` - Twitter application consumer secret  
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- `twitter-source.token` - Twitter access token
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- `twitter-source.tokenSecret` - Twitter access token secret
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**Optional Properties:**
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- `twitter-source.name` - Client name (default: "flink-twitter-source")
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- `twitter-source.hosts` - Twitter API hosts (default: Constants.STREAM_HOST from HBC library)
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- `twitter-source.bufferSize` - Buffer size for reading (default: "50000")
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### Source Lifecycle Methods
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Core lifecycle methods inherited from RichSourceFunction for managing the Twitter streaming connection.
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```java { .api }
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/**
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 * Initializes the source with configuration parameters
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 * @param parameters Configuration from Flink runtime
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 * @throws Exception if initialization fails
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 */
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public void open(Configuration parameters) throws Exception;
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/**
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 * Main execution method that establishes Twitter connection and streams data
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 * @param ctx Source context for emitting collected tweets
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 * @throws Exception if connection or streaming fails
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 */
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public void run(SourceContext<String> ctx) throws Exception;
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/**
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 * Closes the Twitter connection and releases resources
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 */
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public void close();
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/**
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 * Cancels the source operation and stops streaming
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 */
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public void cancel();
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```
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### Custom Endpoint Configuration
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Allows customization of the Twitter streaming endpoint beyond the default sample stream.
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```java { .api }
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/**
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 * Sets a custom endpoint initializer for the Twitter source
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 * @param initializer Custom endpoint initializer implementation
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 * @throws NullPointerException if initializer is null
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 */
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public void setCustomEndpointInitializer(EndpointInitializer initializer)
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```
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### Property Constants
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Pre-defined property key constants for configuration.
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```java { .api }
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// Required property keys
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public static final String CONSUMER_KEY = "twitter-source.consumerKey";
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public static final String CONSUMER_SECRET = "twitter-source.consumerSecret";
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public static final String TOKEN = "twitter-source.token";
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public static final String TOKEN_SECRET = "twitter-source.tokenSecret";
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// Optional property keys  
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public static final String CLIENT_NAME = "twitter-source.name";
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public static final String CLIENT_HOSTS = "twitter-source.hosts";
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public static final String CLIENT_BUFFER_SIZE = "twitter-source.bufferSize";
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```
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## Interfaces
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### EndpointInitializer
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Interface for creating custom Twitter streaming endpoints to override the default sample endpoint behavior.
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```java { .api }
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/**
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 * Interface for creating custom Twitter streaming endpoints
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 */
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public interface EndpointInitializer {
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    /**
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     * Creates and returns a Twitter streaming endpoint
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     * @return StreamingEndpoint instance for Twitter API connection
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     */
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    StreamingEndpoint createEndpoint();
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}
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```
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**Usage Example:**
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```java
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TwitterSource twitterSource = new TwitterSource(properties);
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// Custom endpoint that filters tweets by keywords
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twitterSource.setCustomEndpointInitializer(() -> {
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    StatusesFilterEndpoint endpoint = new StatusesFilterEndpoint();
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    endpoint.trackTerms(Arrays.asList("apache", "flink", "streaming"));
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    return endpoint;
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});
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```
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## Type Definitions
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### Core Flink Types
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```java { .api }
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/**
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 * Base source function interface from Flink
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 */
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public abstract class RichSourceFunction<T> implements SourceFunction<T> {
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    // Lifecycle methods implemented by TwitterSource
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}
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/**
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 * Context for emitting data from sources
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 */
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public interface SourceContext<T> {
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    void collect(T element);
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    // Additional methods for checkpointing and timestamps
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}
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/**
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 * Flink configuration object
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 */
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public class Configuration {
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    // Configuration parameters passed to open() method
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}
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```
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### Twitter HBC Types
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```java { .api }
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/**
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 * Base interface for Twitter streaming endpoints from HBC library
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 */
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public interface StreamingEndpoint {
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    // Twitter endpoint configuration methods
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}
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/**
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 * Sample endpoint implementation (used by default)
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 */
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public class StatusesSampleEndpoint implements StreamingEndpoint {
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    public StatusesSampleEndpoint stallWarnings(boolean stallWarnings);
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    public StatusesSampleEndpoint delimited(boolean delimited);
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}
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/**
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 * Filter endpoint for tracking specific terms
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 */
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public class StatusesFilterEndpoint implements StreamingEndpoint {
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    public StatusesFilterEndpoint trackTerms(List<String> terms);
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    // Additional filtering methods
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}
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```
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## Architecture Notes
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- **Non-parallel Source**: TwitterSource is not parallelizable due to Twitter API connection limitations
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- **Fault Tolerance**: Integrates with Flink's checkpointing mechanism for exactly-once processing
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- **Authentication**: Uses OAuth1 protocol for secure Twitter API access
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- **Rate Limiting**: Handles Twitter API rate limits automatically through HBC library
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- **Data Format**: Emits raw tweet JSON strings for downstream processing
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- **Dependencies**: Built on Twitter's Hosebird Client (HBC) library version 2.2.0
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## Error Handling
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The connector handles several types of errors:
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- **Configuration Errors**: `IllegalArgumentException` thrown during constructor if required properties (`CONSUMER_KEY`, `CONSUMER_SECRET`, `TOKEN`, `TOKEN_SECRET`) are missing
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- **Endpoint Initialization Errors**: `NullPointerException` thrown by `setCustomEndpointInitializer()` if initializer parameter is null
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- **Connection and Runtime Errors**: Handled by the underlying HBC library and Flink's fault tolerance mechanisms
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- **Authentication Errors**: OAuth authentication failures are handled by the HBC client during connection establishment
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- **Stream Processing Errors**: `IOException` and `InterruptedException` can be thrown during stream processing and are propagated to Flink's error handling
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**Exception Hierarchy:**
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```java { .api }
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// Constructor exceptions
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public TwitterSource(Properties properties) throws IllegalArgumentException
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// Lifecycle method exceptions  
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public void open(Configuration parameters) throws Exception
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public void run(SourceContext<String> ctx) throws Exception
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// Configuration method exceptions
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public void setCustomEndpointInitializer(EndpointInitializer initializer) throws NullPointerException
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```