[CHANGE][ISSUE#7426] Add support to convert variant to JSON

Author: carpecodeum

parquet-variant/Cargo.toml

@@ -33,5 +33,6 @@ rust-version = { workspace = true }
 [dependencies]
 arrow-schema = "55.1.0"
 chrono = { workspace = true }
+serde_json = "1.0"
 
 [lib]

parquet-variant/examples/variant_to_json.rs

@@ -0,0 +1,108 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Example showing how to convert Variant values to JSON
+
+use parquet_variant::{
+    variant_to_json, variant_to_json_string, variant_to_json_value, Variant,
+};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let variants = vec![
+        ("Null", Variant::Null),
+        ("Boolean True", Variant::BooleanTrue),
+        ("Boolean False", Variant::BooleanFalse),
+        ("Integer 42", Variant::Int8(42)),
+        ("Negative Integer", Variant::Int8(-123)),
+        ("String", Variant::String("Hello, World!")),
+        ("Short String", Variant::ShortString("Hi!")),
+    ];
+
+    for (name, variant) in variants {
+        let json_string = variant_to_json_string(&variant)?;
+        println!("   {} -> {}", name, json_string);
+    }
+
+    // Example 2: String escaping
+    println!("\n🔤 2. String Escaping:");
+    
+    let special_string = Variant::String("Line 1\nLine 2\tTabbed\r\nWith \"quotes\" and \\backslashes");
+    let escaped_json = variant_to_json_string(&special_string)?;
+    println!("   Original: Line 1\\nLine 2\\tTabbed\\r\\nWith \"quotes\" and \\\\backslashes");
+    println!("   JSON:     {}", escaped_json);
+
+    // Example 3: Unicode support
+    println!("\n🌍 3. Unicode Support:");
+    
+    let unicode_variants = vec![
+        Variant::String("Hello 世界 🌍"),
+        Variant::String("Emoji: 💻"),
+        Variant::String("Math: α + β = γ"),
+    ];
+
+    for variant in unicode_variants {
+        let json_string = variant_to_json_string(&variant)?;
+        println!("   {}", json_string);
+    }
+    
+    let test_variant = Variant::String("Buffer test");
+    
+    // Write to Vec<u8>
+    let mut vec_buffer = Vec::new();
+    variant_to_json(&mut vec_buffer, &test_variant)?;
+    println!("   Vec<u8> buffer: {}", String::from_utf8(vec_buffer)?);
+    
+    // Write to String (through write! macro)
+    let mut string_buffer = String::new();
+    use std::fmt::Write;
+    write!(string_buffer, "Prefix: ")?;
+    
+    // Convert to bytes temporarily to use the Write trait
+    let mut temp_buffer = Vec::new();
+    variant_to_json(&mut temp_buffer, &test_variant)?;
+    string_buffer.push_str(&String::from_utf8(temp_buffer)?);
+    println!("   String buffer: {}", string_buffer);
+    
+    let variants_for_value = vec![
+        Variant::Null,
+        Variant::BooleanTrue,
+        Variant::Int8(100),
+        Variant::String("Value conversion"),
+    ];
+
+    for variant in variants_for_value {
+        let json_value = variant_to_json_value(&variant)?;
+        println!("   {:?} -> {:?}", variant, json_value);
+    }
+    
+    let start = std::time::Instant::now();
+    for i in 0..1000 {
+        let variant = Variant::Int8((i % 128) as i8);
+        let _json = variant_to_json_string(&variant)?;
+    }
+    let duration = start.elapsed();
+    println!("   Converted 1000 variants in {:?}", duration);
+    
+    // This would demonstrate error handling if we had invalid variants
+    // For now, all our examples work, so we'll just show the pattern
+    match variant_to_json_string(&Variant::String("Valid string")) {
+        Ok(json) => println!("   Success: {}", json),
+        Err(e) => println!("   Error: {}", e),
+    }
+
+    Ok(())
+} 

parquet-variant/src/encoder.rs

@@ -0,0 +1,20 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Encoder module for converting Variant values to other formats
+
+pub mod json;