ZipXmlThemeResourceProvider: add method to just scan zip for xml themes (#807)

vtm-android-example/src/org/oscim/android/test/MapsforgeActivity.java

@@ -238,10 +238,9 @@ public class MapsforgeActivity extends MapActivity {
                 return;
 
             try {
-                Uri uri = data.getData();
+                final Uri uri = data.getData();
 
-                final ZipXmlThemeResourceProvider resourceProvider = new ZipXmlThemeResourceProvider(new ZipInputStream(new BufferedInputStream(getContentResolver().openInputStream(uri))));
-                final List<String> xmlThemes = resourceProvider.getXmlThemes();
+                final List<String> xmlThemes = ZipXmlThemeResourceProvider.scanXmlThemes(new ZipInputStream(new BufferedInputStream(getContentResolver().openInputStream(uri))));
                 if (xmlThemes.isEmpty())
                     return;
 
@@ -250,13 +249,17 @@ public class MapsforgeActivity extends MapActivity {
                 builder.setSingleChoiceItems(xmlThemes.toArray(new String[0]), -1, new DialogInterface.OnClickListener() {
                     @Override
                     public void onClick(DialogInterface dialog, int which) {
-                        dialog.dismiss();
-                        ThemeFile theme = new ZipRenderTheme(xmlThemes.get(which), resourceProvider);
-                        if (mTheme != null)
-                            mTheme.dispose();
-                        mTheme = mMap.setTheme(theme);
-                        mapsforgeTheme(mTheme);
-                        mMenu.findItem(R.id.theme_external_archive).setChecked(true);
+                        try {
+                            dialog.dismiss();
+                            ThemeFile theme = new ZipRenderTheme(xmlThemes.get(which), new ZipXmlThemeResourceProvider(new ZipInputStream(new BufferedInputStream(getContentResolver().openInputStream(uri)))));
+                            if (mTheme != null)
+                                mTheme.dispose();
+                            mTheme = mMap.setTheme(theme);
+                            mapsforgeTheme(mTheme);
+                            mMenu.findItem(R.id.theme_external_archive).setChecked(true);
+                        } catch (IOException e) {
+                            e.printStackTrace();
+                        }
                     }
                 });
                 builder.show();

vtm-tests/test/org/oscim/theme/ZipXmlThemeResourceProviderTest.java

@@ -83,4 +83,18 @@ public class ZipXmlThemeResourceProviderTest {
     public void openEmpty() throws IOException {
         Assert.assertTrue(new ZipXmlThemeResourceProvider(null).getXmlThemes().isEmpty());
     }
+
+    @Test
+    public void scanZipForXmlThemes() throws IOException {
+        ZipInputStream zis = new ZipInputStream(new BufferedInputStream(ZipXmlThemeResourceProviderTest.class.getResourceAsStream("/xmlthemetest.zip")));
+        Assert.assertNotNull(zis);
+
+        List<String> xmlThemes = ZipXmlThemeResourceProvider.scanXmlThemes(zis);
+
+        Assert.assertEquals(4, xmlThemes.size());
+        Assert.assertTrue(xmlThemes.contains("one.xml"));
+        Assert.assertTrue(xmlThemes.contains("two.xml"));
+        Assert.assertTrue(xmlThemes.contains("res/three.xml"));
+        Assert.assertTrue(xmlThemes.contains("res/sub/four.xml"));
+    }
 }

vtm/src/org/oscim/theme/ZipXmlThemeResourceProvider.java

@@ -60,12 +60,9 @@ public class ZipXmlThemeResourceProvider implements XmlThemeResourceProvider {
                     continue;
                 }
                 byte[] entry = streamToBytes(zipInputStream, (int) zipEntry.getSize());
-                String fileName = zipEntry.getName();
-                if (fileName.startsWith("/")) {
-                    fileName = fileName.substring(1);
-                }
+                String fileName = zipEntryName(zipEntry.getName());
                 files.put(fileName, entry);
-                if (fileName.toLowerCase(Locale.ROOT).endsWith(".xml")) {
+                if (isXmlTheme(fileName)) {
                     xmlThemes.add(fileName);
                 }
             }
@@ -112,6 +109,45 @@ public class ZipXmlThemeResourceProvider implements XmlThemeResourceProvider {
         return xmlThemes;
     }
 
+    private static boolean isXmlTheme(String fileName) {
+        return fileName.toLowerCase(Locale.ROOT).endsWith(".xml");
+    }
+
+    /**
+     * Scans a given zip stream for contained xml themes without actually reading and storing its content in memory.
+     * <p>
+     * This method is useful to find out which xml themes are available across multiple zip files
+     * without actually have to read them all into memory.
+     *
+     * @param zipInputStream zip stream to read resources from
+     * @return the XML theme paths in the archive
+     * @throws IOException if a problem occurs reading the stream
+     */
+    public static List<String> scanXmlThemes(ZipInputStream zipInputStream) throws IOException {
+        if (zipInputStream == null) {
+            return Collections.emptyList();
+        }
+
+        List<String> xmlThemes = new ArrayList<>();
+
+        try {
+            ZipEntry zipEntry;
+            while ((zipEntry = zipInputStream.getNextEntry()) != null) {
+                if (zipEntry.isDirectory()) {
+                    continue;
+                }
+                String fileName = zipEntryName(zipEntry.getName());
+                if (isXmlTheme(fileName)) {
+                    xmlThemes.add(fileName);
+                }
+            }
+        } finally {
+            IOUtils.closeQuietly(zipInputStream);
+        }
+
+        return xmlThemes;
+    }
+
     private static byte[] streamToBytes(InputStream in, int size) throws IOException {
         byte[] bytes = new byte[size];
         int count, offset = 0;
@@ -121,4 +157,11 @@ public class ZipXmlThemeResourceProvider implements XmlThemeResourceProvider {
         }
         return bytes;
     }
+
+    private static String zipEntryName(String name) {
+        if (name.startsWith("/")) {
+            return name.substring(1);
+        }
+        return name;
+    }
 }