feat(binding/java): make Metadata a POJO (#3277)

bindings/java/src/blocking_operator.rs

@@ -19,12 +19,14 @@ use jni::objects::JByteArray;
 use jni::objects::JClass;
 use jni::objects::JObject;
 use jni::objects::JString;
-use jni::sys::{jbyteArray, jlong};
+use jni::sys::jbyteArray;
+use jni::sys::jobject;
 use jni::JNIEnv;
 
 use opendal::BlockingOperator;
 
 use crate::jstring_to_string;
+use crate::make_metadata;
 use crate::Result;
 
 /// # Safety
@@ -98,17 +100,17 @@ pub unsafe extern "system" fn Java_org_apache_opendal_BlockingOperator_stat(
     _: JClass,
     op: *mut BlockingOperator,
     path: JString,
-) -> jlong {
+) -> jobject {
     intern_stat(&mut env, &mut *op, path).unwrap_or_else(|e| {
         e.throw(&mut env);
-        0
+        JObject::default().into_raw()
     })
 }
 
-fn intern_stat(env: &mut JNIEnv, op: &mut BlockingOperator, path: JString) -> Result<jlong> {
+fn intern_stat(env: &mut JNIEnv, op: &mut BlockingOperator, path: JString) -> Result<jobject> {
     let path = jstring_to_string(env, &path)?;
     let metadata = op.stat(&path)?;
-    Ok(Box::into_raw(Box::new(metadata)) as jlong)
+    Ok(make_metadata(env, metadata)?.into_raw())
 }
 
 /// # Safety

bindings/java/src/lib.rs

@@ -32,13 +32,14 @@ use jni::JavaVM;
 use once_cell::sync::OnceCell;
 use opendal::raw::PresignedRequest;
 use opendal::Capability;
+use opendal::EntryMode;
+use opendal::Metadata;
 use opendal::OperatorInfo;
 use tokio::runtime::Builder;
 use tokio::runtime::Runtime;
 
 mod blocking_operator;
 mod error;
-mod metadata;
 mod operator;
 
 pub(crate) type Result<T> = std::result::Result<T, error::Error>;
@@ -222,6 +223,57 @@ fn make_capability<'a>(env: &mut JNIEnv<'a>, cap: Capability) -> Result<JObject<
     Ok(capability)
 }
 
+fn make_metadata<'a>(env: &mut JNIEnv<'a>, metadata: Metadata) -> Result<JObject<'a>> {
+    let mode = match metadata.mode() {
+        EntryMode::FILE => 0,
+        EntryMode::DIR => 1,
+        EntryMode::Unknown => 2,
+    };
+
+    let last_modified = metadata.last_modified().map_or_else(
+        || Ok::<JObject<'_>, Error>(JObject::null()),
+        |v| {
+            Ok(env.new_object(
+                "java/util/Date",
+                "(J)V",
+                &[JValue::Long(v.timestamp_millis())],
+            )?)
+        },
+    )?;
+
+    let cache_control = string_to_jstring(env, metadata.cache_control())?;
+    let content_disposition = string_to_jstring(env, metadata.content_disposition())?;
+    let content_md5 = string_to_jstring(env, metadata.content_md5())?;
+    let content_type = string_to_jstring(env, metadata.content_type())?;
+    let etag = string_to_jstring(env, metadata.etag())?;
+    let version = string_to_jstring(env, metadata.version())?;
+
+    let result = env
+        .new_object(
+            "org/apache/opendal/Metadata",
+            "(IJLjava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Date;Ljava/lang/String;)V",
+            &[
+                JValue::Int(mode as jint),
+                JValue::Long(metadata.content_length() as jlong),
+                JValue::Object(&content_disposition),
+                JValue::Object(&content_md5),
+                JValue::Object(&content_type),
+                JValue::Object(&cache_control),
+                JValue::Object(&etag),
+                JValue::Object(&last_modified),
+                JValue::Object(&version),
+            ],
+        )?;
+    Ok(result)
+}
+
+fn string_to_jstring<'a>(env: &mut JNIEnv<'a>, s: Option<&str>) -> Result<JObject<'a>> {
+    s.map_or_else(
+        || Ok(JObject::null()),
+        |v| Ok(env.new_string(v.to_string())?.into()),
+    )
+}
+
 /// # Safety
 ///
 /// The caller must guarantee that the Object passed in is an instance

bindings/java/src/main/java/org/apache/opendal/BlockingOperator.java

@@ -67,7 +67,7 @@ public void delete(String path) {
     }
 
     public Metadata stat(String path) {
-        return new Metadata(stat(nativeHandle, path));
+        return stat(nativeHandle, path);
     }
 
     public void createDir(String path) {
@@ -91,7 +91,7 @@ public void rename(String sourcePath, String targetPath) {
 
     private static native void delete(long nativeHandle, String path);
 
-    private static native long stat(long nativeHandle, String path);
+    private static native Metadata stat(long nativeHandle, String path);
 
     private static native long createDir(long nativeHandle, String path);
 

bindings/java/src/main/java/org/apache/opendal/Metadata.java

@@ -19,26 +19,70 @@
 
 package org.apache.opendal;
 
+import java.util.Date;
+import lombok.Data;
+
 /**
  * Metadata carries all metadata associated with a path.
  */
-public class Metadata extends NativeObject {
-    protected Metadata(long nativeHandle) {
-        super(nativeHandle);
+@Data
+public class Metadata {
+    public final EntryMode mode;
+    public final long contentLength;
+    public final String contentDisposition;
+    public final String contentMd5;
+    public final String contentType;
+    public final String cacheControl;
+    public final String etag;
+    public final Date lastModified;
+    public final String version;
+
+    public Metadata(
+            int mode,
+            long contentLength,
+            String contentDisposition,
+            String contentMd5,
+            String contentType,
+            String cacheControl,
+            String etag,
+            Date lastModified,
+            String version) {
+        this.mode = EntryMode.of(mode);
+        this.contentLength = contentLength;
+        this.contentDisposition = contentDisposition;
+        this.contentMd5 = contentMd5;
+        this.contentType = contentType;
+        this.cacheControl = cacheControl;
+        this.etag = etag;
+        this.lastModified = lastModified;
+        this.version = version;
     }
 
     public boolean isFile() {
-        return isFile(nativeHandle);
+        return mode == EntryMode.FILE;
     }
 
-    public long getContentLength() {
-        return getContentLength(nativeHandle);
+    public boolean isDir() {
+        return mode == EntryMode.DIR;
     }
 
-    @Override
-    protected native void disposeInternal(long handle);
+    public enum EntryMode {
+        /// FILE means the path has data to read.
+        FILE,
+        /// DIR means the path can be listed.
+        DIR,
+        /// Unknown means we don't know what we can do on this path.
+        UNKNOWN;
 
-    private static native boolean isFile(long nativeHandle);
-
-    private static native long getContentLength(long nativeHandle);
+        public static EntryMode of(int mode) {
+            switch (mode) {
+                case 0:
+                    return EntryMode.FILE;
+                case 1:
+                    return EntryMode.DIR;
+                default:
+                    return EntryMode.UNKNOWN;
+            }
+        }
+    }
 }

bindings/java/src/main/java/org/apache/opendal/Operator.java

@@ -148,8 +148,7 @@ public CompletableFuture<Void> append(String path, byte[] content) {
 
     public CompletableFuture<Metadata> stat(String path) {
         final long requestId = stat(nativeHandle, path);
-        final CompletableFuture<Long> f = AsyncRegistry.take(requestId);
-        return f.thenApply(Metadata::new);
+        return AsyncRegistry.take(requestId);
     }
 
     public CompletableFuture<byte[]> read(String path) {

bindings/java/src/operator.rs

@@ -35,6 +35,7 @@ use crate::get_current_env;
 use crate::get_global_runtime;
 use crate::jmap_to_hashmap;
 use crate::jstring_to_string;
+use crate::make_metadata;
 use crate::make_operator_info;
 use crate::make_presigned_request;
 use crate::Result;
@@ -181,15 +182,16 @@ fn intern_stat(env: &mut JNIEnv, op: *mut Operator, path: JString) -> Result<jlo
 
     unsafe { get_global_runtime() }.spawn(async move {
         let result = do_stat(op, path).await;
-        complete_future(id, result.map(JValueOwned::Long))
+        complete_future(id, result.map(JValueOwned::Object))
     });
 
     Ok(id)
 }
 
-async fn do_stat(op: &mut Operator, path: String) -> Result<jlong> {
+async fn do_stat<'local>(op: &mut Operator, path: String) -> Result<JObject<'local>> {
     let metadata = op.stat(&path).await?;
-    Ok(Box::into_raw(Box::new(metadata)) as jlong)
+    let mut env = unsafe { get_current_env() };
+    make_metadata(&mut env, metadata)
 }
 
 /// # Safety