Fix file descriptor leaks in ServerStatusManager and ZooKeeperCommandExecutor

Motivation:

`Files.newInputStream()` and `Files.newOutputStream()` allocate real OS
file descriptors. `Properties.load()` and `Properties.store()` do not
close the stream passed to them, so the caller is responsible for
closing it. The descriptors are eventually reclaimed by GC, but GC is
triggered by memory pressure rather than FD exhaustion.

Modifications:

- `ServerStatusManager.serverStatus()`: wrap `Files.newInputStream()`
  in try-with-resources so the stream is closed after `Properties.load()`.
- `ServerStatusManager.updateStatus()`: same fix for the load path;
  also wrap `Files.newOutputStream()` in try-with-resources so the
  stream is closed after `Properties.store()`.

Result:

- File descriptors opened for property file I/O are now released
  deterministically instead of relying on GC finalisation.

Author: minwoox

server/src/main/java/com/linecorp/centraldogma/server/internal/replication/ZooKeeperCommandExecutor.java

@@ -772,19 +772,14 @@ private static boolean shutdown(@Nullable ExecutorService executor) {
     }
 
     private long getLastReplayedRevision() throws Exception {
-        final FileInputStream fis;
-        try {
-            fis = new FileInputStream(revisionFile);
-        } catch (FileNotFoundException ignored) {
-            return -1;
-        }
-
-        try (BufferedReader br = new BufferedReader(new InputStreamReader(fis))) {
+        try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(revisionFile)))) {
             final String l = br.readLine();
             if (l == null) {
                 return -1;
             }
             return Long.parseLong(l.trim());
+        } catch (FileNotFoundException ignored) {
+            return -1;
         }
     }
 

server/src/main/java/com/linecorp/centraldogma/server/management/ServerStatusManager.java

@@ -20,6 +20,8 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Properties;
@@ -65,8 +67,8 @@ public ServerStatusManager(File dataDir) {
     public ServerStatus serverStatus() {
         final Properties properties = new Properties();
         synchronized (serverStatusFile) {
-            try {
-                properties.load(Files.newInputStream(serverStatusFile));
+            try (InputStream in = Files.newInputStream(serverStatusFile)) {
+                properties.load(in);
             } catch (IOException e) {
                 throw new IllegalStateException("Failed to load server status file: " + serverStatusFile, e);
             }
@@ -85,16 +87,15 @@ public ServerStatus serverStatus() {
     public void updateStatus(ServerStatus newServerStatus) {
         synchronized (serverStatusFile) {
             final Properties properties = new Properties();
-            try {
-                properties.load(Files.newInputStream(serverStatusFile));
+            try (InputStream in = Files.newInputStream(serverStatusFile)) {
+                properties.load(in);
             } catch (IOException e) {
                 throw new IllegalStateException("Failed to load server status file: " + serverStatusFile,
                                                 e);
             }
             properties.setProperty(STATUS, newServerStatus.name());
-            try {
-                properties.store(Files.newOutputStream(serverStatusFile),
-                                 "Do not edit this file manually. Use the AdministrativeService API.");
+            try (OutputStream out = Files.newOutputStream(serverStatusFile)) {
+                properties.store(out, "Do not edit this file manually. Use the AdministrativeService API.");
             } catch (IOException e) {
                 throw new IllegalStateException("Failed to store server status file: " + serverStatusFile,
                                                 e);