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# Configuration Utilities
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Utility functions for handling Hadoop configuration, command-line argument parsing, and integration between Hadoop and Flink execution environments. Provides helper methods for common configuration tasks and parameter management.
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## Capabilities
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### Command-Line Parameter Parsing
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Utility for parsing Hadoop-style command-line arguments using GenericOptionsParser.
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```java { .api }
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/**
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 * Returns ParameterTool for the arguments parsed by GenericOptionsParser
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 * @param args Input array arguments that should be parsable by GenericOptionsParser
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 * @return A ParameterTool containing the parsed parameters
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 * @throws IOException If arguments cannot be parsed by GenericOptionsParser
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 * @see GenericOptionsParser
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 */
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public static ParameterTool paramsFromGenericOptionsParser(String[] args) throws IOException;
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```
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**Usage Example:**
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```java
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import org.apache.flink.hadoopcompatibility.HadoopUtils;
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import org.apache.flink.util.ParameterTool;
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public class HadoopCompatibleFlinkJob {
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    public static void main(String[] args) throws Exception {
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        // Parse Hadoop-style command line arguments
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        // Supports arguments like: -D property=value -files file1,file2 -archives archive1
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        ParameterTool parameters = HadoopUtils.paramsFromGenericOptionsParser(args);
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        // Access parsed parameters
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        String inputPath = parameters.get("input.path", "hdfs://default/input");
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        String outputPath = parameters.get("output.path", "hdfs://default/output");
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        int parallelism = parameters.getInt("parallelism", 1);
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        // Use parameters in Flink job configuration
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        ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
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        env.setParallelism(parallelism);
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        // Create configuration from parameters
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        Configuration config = Configuration.fromMap(parameters.toMap());
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        System.out.println("Input path: " + inputPath);
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        System.out.println("Output path: " + outputPath);
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        System.out.println("Parallelism: " + parallelism);
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    }
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}
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```
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### Hadoop Configuration Integration
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Working with Hadoop configuration objects and integrating them with Flink.
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**JobConf Integration:**
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```java
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import org.apache.hadoop.mapred.JobConf;
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import org.apache.flink.util.ParameterTool;
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// Create JobConf from parsed parameters
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public static JobConf createJobConf(ParameterTool parameters) {
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    JobConf jobConf = new JobConf();
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    // Set common Hadoop properties from parameters
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    if (parameters.has("mapred.job.name")) {
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        jobConf.setJobName(parameters.get("mapred.job.name"));
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    }
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    if (parameters.has("mapred.reduce.tasks")) {
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        jobConf.setNumReduceTasks(parameters.getInt("mapred.reduce.tasks"));
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    }
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    // Copy all parameters as properties
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    for (String key : parameters.getProperties().stringPropertyNames()) {
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        jobConf.set(key, parameters.get(key));
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    }
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    return jobConf;
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}
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// Usage example
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String[] args = {"-D", "mapred.job.name=MyFlinkJob", "-D", "input.path=/data/input"};
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ParameterTool params = HadoopUtils.paramsFromGenericOptionsParser(args);
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JobConf jobConf = createJobConf(params);
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```
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**Job (mapreduce API) Integration:**
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```java
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import org.apache.hadoop.mapreduce.Job;
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import org.apache.flink.util.ParameterTool;
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// Create Job from parsed parameters
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public static Job createJob(ParameterTool parameters) throws IOException {
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    Job job = Job.getInstance();
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    // Set common mapreduce properties from parameters
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    if (parameters.has("mapreduce.job.name")) {
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        job.setJobName(parameters.get("mapreduce.job.name"));
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    }
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    if (parameters.has("mapreduce.job.reduces")) {
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        job.setNumReduceTasks(parameters.getInt("mapreduce.job.reduces"));
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    }
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    // Copy all parameters as configuration properties
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    for (String key : parameters.getProperties().stringPropertyNames()) {
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        job.getConfiguration().set(key, parameters.get(key));
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    }
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    return job;
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}
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// Usage example
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String[] args = {"-D", "mapreduce.job.name=MyFlinkJob", "-D", "output.path=/data/output"};
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ParameterTool params = HadoopUtils.paramsFromGenericOptionsParser(args);
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Job job = createJob(params);
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```
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## Advanced Configuration Patterns
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### Environment Variable Integration
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Combining command-line arguments with environment variables.
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```java
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public static ParameterTool createConfigurationFromMultipleSources(String[] args) throws IOException {
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    // Parse command-line arguments
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    ParameterTool cmdLineParams = HadoopUtils.paramsFromGenericOptionsParser(args);
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    // Merge with environment variables
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    ParameterTool envParams = ParameterTool.fromSystemProperties();
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    // Merge with properties file if specified
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    ParameterTool allParams = cmdLineParams;
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    if (cmdLineParams.has("config.file")) {
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        ParameterTool fileParams = ParameterTool.fromPropertiesFile(cmdLineParams.get("config.file"));
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        allParams = fileParams.mergeWith(cmdLineParams); // Command line overrides file
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    }
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    // Environment variables have lowest priority
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    allParams = allParams.mergeWith(envParams);
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    return allParams;
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}
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// Usage
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String[] args = {"-D", "parallelism=4", "--config.file", "app.properties"};
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ParameterTool config = createConfigurationFromMultipleSources(args);
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```
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### Configuration Validation
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Validating and processing configuration parameters.
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```java
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public static class ConfigurationValidator {
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    public static void validateRequiredParameters(ParameterTool params, String... requiredKeys) 
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            throws IllegalArgumentException {
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        for (String key : requiredKeys) {
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            if (!params.has(key)) {
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                throw new IllegalArgumentException("Required parameter missing: " + key);
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            }
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        }
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    }
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    public static void validatePaths(ParameterTool params) throws IOException {
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        if (params.has("input.path")) {
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            String inputPath = params.get("input.path");
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            // Validate input path exists (for HDFS paths, would need Hadoop FileSystem)
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            if (!inputPath.startsWith("hdfs://") && !inputPath.startsWith("file://")) {
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                throw new IllegalArgumentException("Invalid input path format: " + inputPath);
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            }
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        }
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        if (params.has("output.path")) {
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            String outputPath = params.get("output.path");
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            // Validate output path format
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            if (!outputPath.startsWith("hdfs://") && !outputPath.startsWith("file://")) {
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                throw new IllegalArgumentException("Invalid output path format: " + outputPath);
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            }
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        }
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    }
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    public static int getValidatedParallelism(ParameterTool params, int defaultValue, int maxValue) {
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        int parallelism = params.getInt("parallelism", defaultValue);
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        if (parallelism < 1 || parallelism > maxValue) {
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            throw new IllegalArgumentException(
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                "Parallelism must be between 1 and " + maxValue + ", got: " + parallelism);
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        }
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        return parallelism;
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    }
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}
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// Usage example
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public static void main(String[] args) throws Exception {
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    ParameterTool params = HadoopUtils.paramsFromGenericOptionsParser(args);
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    // Validate configuration
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    ConfigurationValidator.validateRequiredParameters(params, "input.path", "output.path");
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    ConfigurationValidator.validatePaths(params);
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    int parallelism = ConfigurationValidator.getValidatedParallelism(params, 1, 100);
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    // Use validated configuration
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    ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
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    env.setParallelism(parallelism);
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}
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```
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### Resource Management Integration
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Integrating with Hadoop resource management and file systems.
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```java
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import org.apache.hadoop.fs.FileSystem;
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import org.apache.hadoop.fs.Path;
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import org.apache.hadoop.conf.Configuration;
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public static class ResourceManager {
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    public static Configuration createHadoopConfiguration(ParameterTool params) {
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        Configuration conf = new Configuration();
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        // Set HDFS configuration from parameters
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        if (params.has("fs.defaultFS")) {
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            conf.set("fs.defaultFS", params.get("fs.defaultFS"));
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        }
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        if (params.has("hadoop.conf.dir")) {
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            // Add Hadoop configuration directory to classpath
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            String confDir = params.get("hadoop.conf.dir");
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            conf.addResource(new Path(confDir + "/core-site.xml"));
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            conf.addResource(new Path(confDir + "/hdfs-site.xml"));
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            conf.addResource(new Path(confDir + "/mapred-site.xml"));
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        }
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        // Copy all hadoop.* properties
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        for (String key : params.getProperties().stringPropertyNames()) {
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            if (key.startsWith("hadoop.") || key.startsWith("fs.") || key.startsWith("dfs.")) {
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                conf.set(key, params.get(key));
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            }
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        }
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        return conf;
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    }
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    public static boolean validateInputPath(String inputPath, Configuration hadoopConf) throws IOException {
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        FileSystem fs = FileSystem.get(hadoopConf);
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        Path path = new Path(inputPath);
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        return fs.exists(path);
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    }
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    public static void ensureOutputPath(String outputPath, Configuration hadoopConf) throws IOException {
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        FileSystem fs = FileSystem.get(hadoopConf);
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        Path path = new Path(outputPath);
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        if (fs.exists(path)) {
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            fs.delete(path, true); // Delete existing output directory
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        }
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        // Create parent directories if they don't exist
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        Path parent = path.getParent();
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        if (parent != null && !fs.exists(parent)) {
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            fs.mkdirs(parent);
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        }
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    }
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}
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```
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## Common Usage Patterns
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### Complete Job Configuration
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Example of a complete Flink job using Hadoop utilities for configuration.
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```java
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public class CompleteHadoopFlinkJob {
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    public static void main(String[] args) throws Exception {
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        // Parse Hadoop-style arguments
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        ParameterTool params = HadoopUtils.paramsFromGenericOptionsParser(args);
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        // Validate required parameters
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        if (!params.has("input") || !params.has("output")) {
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            System.err.println("Usage: program -D input=<path> -D output=<path> [options]");
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            System.exit(1);
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        }
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        // Set up execution environment
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        ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
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        env.getConfig().setGlobalJobParameters(params);
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        // Configure parallelism
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        if (params.has("parallelism")) {
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            env.setParallelism(params.getInt("parallelism"));
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        }
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        // Create Hadoop configuration
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        JobConf jobConf = new JobConf();
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        jobConf.set("mapred.input.dir", params.get("input"));
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        jobConf.set("mapred.output.dir", params.get("output"));
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        // Create input format
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        HadoopInputFormat<LongWritable, Text> inputFormat = 
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            HadoopInputs.readHadoopFile(
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                new TextInputFormat(),
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                LongWritable.class,
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                Text.class,
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                params.get("input"),
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                jobConf
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            );
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        // Process data
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        DataSet<Tuple2<LongWritable, Text>> input = env.createInput(inputFormat);
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        DataSet<Tuple2<Text, IntWritable>> result = input
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            .flatMap(new WordCountMapper())
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            .groupBy(0)
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            .sum(1);
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        // Create output format
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        JobConf outputJobConf = new JobConf();
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        outputJobConf.set("mapred.output.dir", params.get("output"));
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        outputJobConf.setOutputFormat(TextOutputFormat.class);
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        HadoopOutputFormat<Text, IntWritable> outputFormat = 
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            new HadoopOutputFormat<>(
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                new TextOutputFormat<Text, IntWritable>(),
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                outputJobConf
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            );
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        // Write results
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        result.output(outputFormat);
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        // Execute job
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        env.execute("Hadoop Compatible Flink Job");
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    }
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}
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```
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### Parameter Processing Utilities
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Utility methods for common parameter processing tasks.
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```java
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public static class ParameterUtils {
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    public static String[] getInputPaths(ParameterTool params) {
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        String input = params.get("input", "");
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        return input.split(",");
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    }
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    public static String getOutputPath(ParameterTool params) {
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        return params.getRequired("output");
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    }
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    public static Map<String, String> getHadoopProperties(ParameterTool params) {
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        Map<String, String> hadoopProps = new HashMap<>();
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        for (String key : params.getProperties().stringPropertyNames()) {
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            if (key.startsWith("hadoop.") || key.startsWith("mapred.") || 
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                key.startsWith("mapreduce.") || key.startsWith("fs.") || key.startsWith("dfs.")) {
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                hadoopProps.put(key, params.get(key));
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            }
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        }
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        return hadoopProps;
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    }
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    public static JobConf createJobConfFromParams(ParameterTool params) {
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        JobConf jobConf = new JobConf();
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        getHadoopProperties(params).forEach(jobConf::set);
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        return jobConf;
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    }
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    public static Job createJobFromParams(ParameterTool params) throws IOException {
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        Job job = Job.getInstance();
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        getHadoopProperties(params).forEach((key, value) -> 
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            job.getConfiguration().set(key, value));
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        return job;
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    }
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}
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```
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## Key Design Patterns
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### Parameter Inheritance
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Command-line parameters parsed by GenericOptionsParser can be easily converted to ParameterTool and then propagated to both Flink and Hadoop configurations.
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### Configuration Layering
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Multiple configuration sources (command-line, files, environment variables) can be layered with appropriate precedence rules.
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### Validation and Error Handling
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Configuration validation should be performed early in the application lifecycle with clear error messages for missing or invalid parameters.
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### Resource Management
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Integration with Hadoop FileSystem and resource management APIs enables proper handling of distributed file operations and cluster resources.