Complete DataFrame Spring integration implementation with issue-speci…

…fic demo

Co-authored-by: zaleslaw <[email protected]>

dataframe-spring/src/main/kotlin/org/jetbrains/kotlinx/dataframe/spring/examples/IssueDemo.kt

@@ -0,0 +1,98 @@
+package org.jetbrains.kotlinx.dataframe.spring.examples
+
+import org.jetbrains.kotlinx.dataframe.DataFrame
+import org.jetbrains.kotlinx.dataframe.annotations.DataSchema
+import org.jetbrains.kotlinx.dataframe.spring.DataFramePostProcessor
+import org.jetbrains.kotlinx.dataframe.spring.annotations.DataSource
+import org.springframework.stereotype.Component
+import java.io.File
+
+/**
+ * This example demonstrates the exact usage pattern specified in the GitHub issue.
+ * It shows how to use @DataSource annotation in Spring DI style to automatically
+ * populate DataFrame properties from CSV files.
+ */
+
+@DataSchema
+interface MyRowType {
+    val id: Int
+    val name: String
+    val value: Double
+}
+
+/**
+ * Example service class using @DataSource annotation exactly as specified in the issue
+ */
+@Component
+class MyDataService {
+    @DataSource(csvFile = "data.csv")
+    lateinit var df: DataFrame<MyRowType>
+
+    fun process() {
+        println("Processing DataFrame with ${df.rowsCount()} rows")
+
+        // Access data using DataFrame API
+        if (df.rowsCount() > 0) {
+            println("First row: ${df[0]}")
+            println("Column names: ${df.columnNames()}")
+        }
+    }
+}
+
+/**
+ * Demonstration of the complete Spring-style integration
+ */
+fun main() {
+    println("=== DataFrame Spring Integration Demo ===")
+    println("Demonstrating exact usage pattern from GitHub issue #1321")
+    println()
+
+    // Create sample data file
+    createSampleDataFile()
+
+    try {
+        // This simulates Spring's bean initialization process
+        println("1. Creating Spring bean...")
+        val myDataService = MyDataService()
+
+        println("2. Running DataFramePostProcessor...")
+        val postProcessor = DataFramePostProcessor()
+        postProcessor.postProcessBeforeInitialization(myDataService, "myDataService")
+
+        println("3. DataFrame loaded successfully!")
+        println("   - CSV file: data.csv")
+        println("   - Rows loaded: ${myDataService.df.rowsCount()}")
+        println("   - Columns: ${myDataService.df.columnNames()}")
+
+        println("4. Running business logic...")
+        myDataService.process()
+
+        println()
+        println("✅ SUCCESS: Spring-style DataFrame initialization completed!")
+        println("✅ The @DataSource annotation automatically loaded CSV data")
+        println("✅ No manual DataFrame construction required")
+        println("✅ Follows Spring DI patterns perfectly")
+
+    } catch (e: Exception) {
+        println("❌ ERROR: ${e.message}")
+        e.printStackTrace()
+    } finally {
+        // Clean up
+        File("data.csv").delete()
+    }
+}
+
+/**
+ * Creates the sample CSV file used in the example
+ */
+private fun createSampleDataFile() {
+    File("data.csv").writeText("""
+        id,name,value
+        1,First Item,100.5
+        2,Second Item,200.0
+        3,Third Item,150.75
+        4,Fourth Item,300.25
+    """.trimIndent())
+
+    println("Created sample data.csv file")
+}