Add persistence

Signed-off-by: Yuuta Liang <yuutaw@student.cs.ubc.ca>

1 files changed, 46 insertions, 0 deletions

diff --git a/src/main/persistence/FS.java b/src/main/persistence/FS.java
new file mode 100644
index 0000000..3b5222d
--- /dev/null
+++ b/src/main/persistence/FS.java
@@ -0,0 +1,46 @@
+package persistence;
+
+import model.asn1.exceptions.InvalidDBException;
+import org.json.JSONException;
+import org.json.JSONObject;
+import org.json.JSONTokener;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+
+/**
+ * Util class for file-system IO.
+ */
+public class FS {
+    /**
+     * EFFECTS: Read and decode the content of given path as UTF-8 into JSON.
+     * Throws {@link InvalidDBException} if IO error occurs or the input cannot be parsed.
+     */
+    public static JSONObject read(Path path) throws InvalidDBException {
+        try {
+            final InputStream fd = Files.newInputStream(path, StandardOpenOption.READ);
+            final JSONObject obj = new JSONObject(new JSONTokener(fd));
+            fd.close();
+            return obj;
+        } catch (IOException | JSONException e) {
+            throw new InvalidDBException("Cannot read or parse the file", e);
+        }
+    }
+
+    /**
+     * EFFECTS: Write the UTF-8 encoded JSON to the given path.
+     * open(2) parameters: <pre>O_WRONLY | O_TRUNC | O_CREAT</pre>
+     * Throws {@link IOException} if the file cannot be opened or written.
+     */
+    public static void write(Path path, JSONObject obj) throws IOException {
+        final OutputStream fd = Files.newOutputStream(path,
+                StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.CREATE);
+        fd.write(obj.toString().getBytes(StandardCharsets.UTF_8));
+        fd.close();
+    }
+}