1 /* 2 * Copyright (C) 2013 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.example.android.common.assetprovider; 18 19 import android.content.ContentProvider; 20 import android.content.ContentValues; 21 import android.content.Context; 22 import android.content.res.AssetFileDescriptor; 23 import android.content.res.AssetManager; 24 import android.database.Cursor; 25 import android.net.Uri; 26 27 import java.io.FileNotFoundException; 28 import java.io.IOException; 29 30 import static java.net.URLConnection.guessContentTypeFromName; 31 32 /** 33 * Generic content provider, which makes any files available in this app's "assets" directory 34 * available publicly. 35 * 36 * <p>To use, add the following to your AndroidManifest.xml: 37 * 38 * <code><pre> 39 * <provider 40 * android:name=".AssetProvider" 41 * android:authorities="[YOUR CONTENT PROVIDER DOMAIN HERE]" 42 * android:exported="true"/> 43 * </pre></code> 44 */ 45 public class AssetProvider extends ContentProvider { 46 AssetManager mAssets; 47 48 @Override onCreate()49 public boolean onCreate() { 50 Context ctx = getContext(); 51 if (ctx == null) { 52 // Context not available. Give up. 53 return false; 54 } 55 mAssets = ctx.getAssets(); 56 return true; 57 } 58 59 @Override getType(Uri uri)60 public String getType(Uri uri){ 61 // Returns the MIME type for the selected URI, in conformance with the ContentProvider 62 // interface. Looks up the file indicated by /res/assets/{uri.path}, and returns the MIME 63 // type for that file as guessed by the URLConnection class. 64 65 // Setup 66 String path = uri.getPath(); 67 68 // Check if file exists 69 if (!fileExists(path)) { 70 return null; 71 } 72 73 // Determine MIME-type based on filename 74 return guessContentTypeFromName(uri.toString()); 75 } 76 77 78 @Override openAssetFile(Uri uri, String mode)79 public AssetFileDescriptor openAssetFile (Uri uri, String mode) 80 throws FileNotFoundException, SecurityException { 81 // ContentProvider interface for opening a file descriptor by URI. This content provider 82 // maps all URIs to the contents of the APK's assets folder, so a file handle to 83 // /res/assets/{uri.path} will be returned. 84 85 // Security check. This content provider only supports read-only access. (Also, the contents 86 // of an APKs assets folder are immutable, so read-write access doesn't make sense here.) 87 if (!"r".equals(mode)) { 88 throw new SecurityException("Only read-only access is supported, mode must be [r]"); 89 } 90 91 // Open asset from within APK and return file descriptor 92 String path = uri.getPath(); 93 try { 94 return mAssets.openFd(path); 95 } catch (IOException e) { 96 throw new FileNotFoundException(); 97 } 98 } 99 100 /** 101 * Check if file exists inside APK assets. 102 * 103 * @param path Fully qualified path to file. 104 * @return true if exists, false otherwise. 105 */ fileExists(String path)106 private boolean fileExists(String path) { 107 try { 108 // Check to see if file can be opened. If so, file exists. 109 mAssets.openFd(path).close(); 110 return true; 111 } catch (IOException e) { 112 // Unable to open file descriptor for specified path; file doesn't exist. 113 return false; 114 } 115 } 116 117 // Required/unused ContentProvider methods below. 118 @Override query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)119 public Cursor query(Uri uri, String[] projection, String selection, 120 String[] selectionArgs, String sortOrder) { 121 // Note: It might be worth implementing support for querying 122 // android.provider.OpenableColumns here in the future. 123 throw new RuntimeException("Operation not supported"); 124 } 125 126 @Override insert(Uri uri, ContentValues contentValues)127 public Uri insert(Uri uri, ContentValues contentValues) { 128 throw new RuntimeException("Operation not supported"); 129 } 130 131 @Override delete(Uri uri, String selection, String[] selectionArgs)132 public int delete(Uri uri, String selection, String[] selectionArgs) { 133 throw new RuntimeException("Operation not supported"); 134 } 135 136 @Override update(Uri uri, ContentValues values, String selection, String[] selectionArgs)137 public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { 138 throw new RuntimeException("Operation not supported"); 139 } 140 } 141