public class Utils {
public static List<Message> getMessages() {
//File file = new File("file:///android_asset/helloworld.txt");
AssetManager assetManager = getAssets();
InputStream ims = assetManager.open("helloworld.txt");
}
}
我正在使用这段代码试图从资产读取文件。我尝试了两种方法。首先，当使用文件时，我收到FileNotFoundException，当使用资产管理器getAssets()方法不被识别。 有什么解决办法吗?
当前回答
AssetManager assetManager = getAssets();
InputStream inputStream = null;
try {
inputStream = assetManager.open("helloworld.txt");
}
catch (IOException e){
Log.e("message: ",e.getMessage());
}
其他回答
在MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tvView = (TextView) findViewById(R.id.tvView);
AssetsReader assetsReader = new AssetsReader(this);
if(assetsReader.getTxtFile(your_file_title)) != null)
{
tvView.setText(assetsReader.getTxtFile(your_file_title)));
}
}
此外，您还可以创建单独的类来完成所有工作
public class AssetsReader implements Readable{
private static final String TAG = "AssetsReader";
private AssetManager mAssetManager;
private Activity mActivity;
public AssetsReader(Activity activity) {
this.mActivity = activity;
mAssetManager = mActivity.getAssets();
}
@Override
public String getTxtFile(String fileName)
{
BufferedReader reader = null;
InputStream inputStream = null;
StringBuilder builder = new StringBuilder();
try{
inputStream = mAssetManager.open(fileName);
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while((line = reader.readLine()) != null)
{
Log.i(TAG, line);
builder.append(line);
builder.append("\n");
}
} catch (IOException ioe){
ioe.printStackTrace();
} finally {
if(inputStream != null)
{
try {
inputStream.close();
} catch (IOException ioe){
ioe.printStackTrace();
}
}
if(reader != null)
{
try {
reader.close();
} catch (IOException ioe)
{
ioe.printStackTrace();
}
}
}
Log.i(TAG, "builder.toString(): " + builder.toString());
return builder.toString();
}
}
在我看来，最好创建一个界面，但这不是必要的
public interface Readable {
/**
* Reads txt file from assets
* @param fileName
* @return string
*/
String getTxtFile(String fileName);
}
cityfile.txt
public void getCityStateFromLocal() {
AssetManager am = getAssets();
InputStream inputStream = null;
try {
inputStream = am.open("city_state.txt");
} catch (IOException e) {
e.printStackTrace();
}
ObjectMapper mapper = new ObjectMapper();
Map<String, String[]> map = new HashMap<String, String[]>();
try {
map = mapper.readValue(getStringFromInputStream(inputStream), new TypeReference<Map<String, String[]>>() {
});
} catch (IOException e) {
e.printStackTrace();
}
ConstantValues.arrayListStateName.clear();
ConstantValues.arrayListCityByState.clear();
if (map.size() > 0)
{
for (Map.Entry<String, String[]> e : map.entrySet()) {
CityByState cityByState = new CityByState();
String key = e.getKey();
String[] value = e.getValue();
ArrayList<String> s = new ArrayList<String>(Arrays.asList(value));
ConstantValues.arrayListStateName.add(key);
s.add(0,"Select City");
cityByState.addValue(s);
ConstantValues.arrayListCityByState.add(cityByState);
}
}
ConstantValues.arrayListStateName.add(0,"Select States");
}
// Convert InputStream to String
public String getStringFromInputStream(InputStream is) {
BufferedReader br = null;
StringBuilder sb = new StringBuilder();
String line;
try {
br = new BufferedReader(new InputStreamReader(is));
while ((line = br.readLine()) != null) {
sb.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return sb + "";
}
getAssets()
它只适用于其他任何类的活动，你必须为它使用上下文。
让Utils类的构造函数将活动引用(丑陋的方式)或应用程序上下文作为参数传递给它。在Utils类中使用getAsset()。
下面是一个在资产中读取文件的方法:
/**
* Reads the text of an asset. Should not be run on the UI thread.
*
* @param mgr
* The {@link AssetManager} obtained via {@link Context#getAssets()}
* @param path
* The path to the asset.
* @return The plain text of the asset
*/
public static String readAsset(AssetManager mgr, String path) {
String contents = "";
InputStream is = null;
BufferedReader reader = null;
try {
is = mgr.open(path);
reader = new BufferedReader(new InputStreamReader(is));
contents = reader.readLine();
String line = null;
while ((line = reader.readLine()) != null) {
contents += '\n' + line;
}
} catch (final Exception e) {
e.printStackTrace();
} finally {
if (is != null) {
try {
is.close();
} catch (IOException ignored) {
}
}
if (reader != null) {
try {
reader.close();
} catch (IOException ignored) {
}
}
}
return contents;
}
以下是我在缓冲读取扩展/修改活动中所做的工作，以满足您的需求
BufferedReader reader = null;
try {
reader = new BufferedReader(
new InputStreamReader(getAssets().open("filename.txt")));
// do reading, usually loop until end of file reading
String mLine;
while ((mLine = reader.readLine()) != null) {
//process line
...
}
} catch (IOException e) {
//log the exception
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
//log the exception
}
}
}
编辑:如果你的问题是关于如何在活动之外做这件事，我的回答可能是无用的。如果你的问题只是如何从资产读取文件，那么答案在上面。
更新:
要打开指定类型的文件，只需在InputStreamReader调用中添加类型，如下所示。
BufferedReader reader = null;
try {
reader = new BufferedReader(
new InputStreamReader(getAssets().open("filename.txt"), "UTF-8"));
// do reading, usually loop until end of file reading
String mLine;
while ((mLine = reader.readLine()) != null) {
//process line
...
}
} catch (IOException e) {
//log the exception
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
//log the exception
}
}
}
EDIT
正如@Stan在评论中所说，我给出的代码不是对行求和。mLine每次传递都会被替换。这就是为什么我写了//process行。我假设文件包含某种类型的数据(即联系人列表)，每一行都应该单独处理。
如果你只是想在没有任何处理的情况下加载文件，你必须在每次传递时使用StringBuilder()对mLine求和并追加每个传递。
另一个编辑
根据@Vincent的评论，我添加了最后一个块。
还要注意，在Java 7及以上版本中，您可以使用try-with-resources来使用最新Java的AutoCloseable和Closeable特性。
上下文
@LunarWatcher在评论中指出getAssets()是上下文中的一个类。因此，如果你在活动之外调用它，你需要引用它并将上下文实例传递给活动。
ContextInstance.getAssets();
这在@Maneesh的回答中有解释。所以如果这对你有用的话，给他的答案投上一票因为是他指出了这一点。
