fix: put java commands behind feature flag

Cargo.toml

@@ -41,3 +41,4 @@ rifgen = { git = "https://github.com/Kofituo/rifgen.git", rev = "d27d9785b2febcf
 [features]
 default = []
 java = ["lazy_static", "jni", "jni-sys", "flapigen", "rifgen", "log"]
+java-artifact = ["java"]

build.rs

@@ -37,7 +37,12 @@ fn main() {
 			out_dir.join("glue.rs")
 		);
 
-		//TODO panic if no jdk
+		#[cfg(feature = "java-artifact")] {
+			// panic if no jdk
+			std::process::Command::new("javac")
+				.arg("--version")
+				.status()
+				.expect("java not found");
 
 			// compile java code
 			let mut java_compiled = java_target.clone(); // target/debug/java/classes
@@ -68,6 +73,7 @@ fn main() {
 
 			println!("cargo:rerun-if-changed={}", generated_glue_file.display());
 		}
+	}
 }
 
 fn recreate_path(path: &std::path::PathBuf) {