Initial implementation of OpenDocumentGuide.

common/src/main/java/com/proculite/androidagain/common/storageaccess/InputStreamHandler.java

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+package com.proculite.androidagain.common.storageaccess;
+
+import java.io.InputStream;
+
+public interface InputStreamHandler {
+    void handleInputStream(InputStream inputStream);
+}

common/src/main/java/com/proculite/androidagain/common/storageaccess/OpenDocumentGuide.java

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+package com.proculite.androidagain.common.storageaccess;
+
+import android.content.Context;
+import android.net.Uri;
+import android.util.Log;
+
+import androidx.activity.result.ActivityResultCallback;
+import androidx.activity.result.ActivityResultCaller;
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+
+public class OpenDocumentGuide implements ActivityResultCallback<Uri> {
+    private final String TAG = ActivityResultContracts.OpenDocument.class.getName();
+    private final ActivityResultLauncher<String[]> openDocumentLauncher;
+    private final Context context;
+    private UriHandler uriHandler;
+
+    public OpenDocumentGuide(
+            Context context,
+            ActivityResultCaller activityResultCaller
+    ) {
+        this.context = context;
+        ActivityResultContracts.OpenDocument openDocumentContract =
+                new ActivityResultContracts.OpenDocument();
+        openDocumentLauncher = activityResultCaller.registerForActivityResult(openDocumentContract, this);
+    }
+
+    @Override
+    public void onActivityResult(Uri o) {
+        uriHandler.handleUri(o);
+    }
+
+    public void readFromInputStream(String[] suggestedMimeTypes, InputStreamHandler inputStreamHandler){
+        uriHandler = uri -> {
+            try {
+                InputStream inputStream = context.getContentResolver().openInputStream(uri);
+                if(inputStream == null)
+                {
+                    Log.e(TAG, "Obtained input stream is null.");
+                    return;
+                }
+                inputStreamHandler.handleInputStream(inputStream);
+                inputStream.close();
+            }catch (FileNotFoundException e){
+                Log.e(TAG, "FileNotFoundException occurred on read from InputStream.");
+            } catch (IOException e) {
+                Log.e(TAG, "IOException occurred on read from InputStream.");
+            }
+        };
+
+        openDocumentLauncher.launch(suggestedMimeTypes);
+    }
+}