diff --git a/core/src/main/java/hudson/ClassicPluginStrategy.java b/core/src/main/java/hudson/ClassicPluginStrategy.java
index 8d24cbed0759f8fcd8f6d9f15d78d53e1d4c505d..481fa468712fc9e6fbe919c87727145a76750118 100644
--- a/core/src/main/java/hudson/ClassicPluginStrategy.java
+++ b/core/src/main/java/hudson/ClassicPluginStrategy.java
@@ -441,7 +441,7 @@ public class ClassicPluginStrategy implements PluginStrategy {
      * Repackage classes directory into a jar file to make it remoting friendly.
      * The remoting layer can cache jar files but not class files.
      */
-    private static void createClassJarFromWebInfClasses(File archive, File destDir, Project prj) {
+    private static void createClassJarFromWebInfClasses(File archive, File destDir, Project prj) throws IOException {
         File classesJar = new File(destDir, "WEB-INF/lib/classes.jar");
 
         ZipFileSet zfs = new ZipFileSet();
@@ -458,31 +458,36 @@ public class ClassicPluginStrategy implements PluginStrategy {
         mapper.add(gm);
 
         final long dirTime = archive.lastModified();
-        Zip z = new Zip() {
-            /**
-             * Forces the fixed timestamp for directories to make sure
-             * classes.jar always get a consistent checksum.
-             */
-            protected void zipDir(Resource dir, ZipOutputStream zOut, String vPath,
-                                  int mode, ZipExtraField[] extra)
-                throws IOException {
-
-                ZipOutputStream wrapped = new ZipOutputStream(new NullOutputStream()) {
-                    @Override
-                    public void putNextEntry(ZipEntry ze) throws IOException {
-                        ze.setTime(dirTime+1999);   // roundup
-                        super.putNextEntry(ze);
-                    }
-                };
-                super.zipDir(dir,wrapped,vPath,mode,extra);
+        // this ZipOutputStream is reused and not created for each directory
+        final ZipOutputStream wrappedZOut = new ZipOutputStream(new NullOutputStream()) {
+            @Override
+            public void putNextEntry(ZipEntry ze) throws IOException {
+                ze.setTime(dirTime+1999);   // roundup
+                super.putNextEntry(ze);
             }
         };
-        z.setProject(prj);
-        z.setTaskType("zip");
-        classesJar.getParentFile().mkdirs();
-        z.setDestFile(classesJar);
-        z.add(mapper);
-        z.execute();
+        try {
+            Zip z = new Zip() {
+                /**
+                 * Forces the fixed timestamp for directories to make sure
+                 * classes.jar always get a consistent checksum.
+                 */
+                protected void zipDir(Resource dir, ZipOutputStream zOut, String vPath,
+                                      int mode, ZipExtraField[] extra)
+                    throws IOException {
+                    // use wrappedZOut instead of zOut
+                    super.zipDir(dir,wrappedZOut,vPath,mode,extra);
+                }
+            };
+            z.setProject(prj);
+            z.setTaskType("zip");
+            classesJar.getParentFile().mkdirs();
+            z.setDestFile(classesJar);
+            z.add(mapper);
+            z.execute();
+        } finally {
+            wrappedZOut.close();
+        }
     }
 
     private static void unzipExceptClasses(File archive, File destDir, Project prj) {
diff --git a/core/src/main/java/hudson/FilePath.java b/core/src/main/java/hudson/FilePath.java
index 61bf466600f92338e8957360bcaaab76e0d1a71e..b2564edc70afb7de07ef5e418dd62ce1ee16e256 100644
--- a/core/src/main/java/hudson/FilePath.java
+++ b/core/src/main/java/hudson/FilePath.java
@@ -530,7 +530,12 @@ public final class FilePath implements Serializable {
                     if (p != null) {
                         p.mkdirs();
                     }
-                    IOUtils.copy(zip.getInputStream(e), f);
+                    InputStream input = zip.getInputStream(e);
+                    try {
+                        IOUtils.copy(input, f);
+                    } finally {
+                        input.close();
+                    }
                     try {
                         FilePath target = new FilePath(f);
                         int mode = e.getUnixMode();