Question

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");    
     }
}

我正在使用此代码尝试从资源中读取文件。我尝试了两种方法来做到这一点。首先，当我使用File时，我收到FileNotFoundException时，使用AssetManager getAssets()方法时无法识别。这里有解决方案吗？

Answer 1

以下是我在缓冲阅读扩展/修改活动中所做的工作

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：如果您的问题是如何在活动之外进行，我的回答可能毫无用处。如果您的问题只是如何从资产中读取文件，那么答案就在上面。

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
         }
    }
}

修改

正如@Stan在评论中所说，我给出的代码并不是总结线条。每次传递都会替换mLine。这就是我写//process line的原因。我假设该文件包含某种数据（即联系人列表），每行应单独处理。

如果您只想加载文件而不进行任何处理，则必须使用mLine在每次传递中总结StringBuilder()并附加每个传递。

另一个编辑

根据@Vincent的评论，我添加了finally块。

另请注意，在Java 7及更高版本中，您可以使用try-with-resources来使用最近Java的AutoCloseable和Closeable功能。

<强> CONTEXT

在评论中@LunarWatcher指出getAssets()是class中的context。因此，如果您在activity之外调用它，则需要引用它并将上下文实例传递给活动。

ContextInstance.getAssets();

@Maneesh的答案解释了这一点。所以，如果这对你的回答很有帮助，那就是那个指出这一点的人。

Answer 2

getAssets()

只能在其他任何类中使用在活动中使用Context。

为Utils 类创建构造函数将活动（丑陋方式）或应用程序上下文的引用作为参数传递给它。使用它在您的Utils类中使用getAsset（）。

Answer 3

迟到总比没有好。

在某些情况下，我无法逐行阅读文件。以下方法是我发现的最好的方法，到目前为止，我推荐它。

用法：String yourData = LoadData("YourDataFile.txt");

假设 YourDataFile.txt 位于 assets /

中

 public String LoadData(String inFile) {
        String tContents = "";

    try {
        InputStream stream = getAssets().open(inFile);

        int size = stream.available();
        byte[] buffer = new byte[size];
        stream.read(buffer);
        stream.close();
        tContents = new String(buffer);
    } catch (IOException e) {
        // Handle exceptions here
    }

    return tContents;

 }

Answer 4

public String ReadFromfile(String fileName, Context context) {
    StringBuilder returnString = new StringBuilder();
    InputStream fIn = null;
    InputStreamReader isr = null;
    BufferedReader input = null;
    try {
        fIn = context.getResources().getAssets()
                .open(fileName, Context.MODE_WORLD_READABLE);
        isr = new InputStreamReader(fIn);
        input = new BufferedReader(isr);
        String line = "";
        while ((line = input.readLine()) != null) {
            returnString.append(line);
        }
    } catch (Exception e) {
        e.getMessage();
    } finally {
        try {
            if (isr != null)
                isr.close();
            if (fIn != null)
                fIn.close();
            if (input != null)
                input.close();
        } catch (Exception e2) {
            e2.getMessage();
        }
    }
    return returnString.toString();
}

Answer 5

AssetManager assetManager = getAssets();
InputStream inputStream = null;
try {
    inputStream = assetManager.open("helloworld.txt");
}
catch (IOException e){
    Log.e("message: ",e.getMessage());
}

Answer 6

在Activity类中调用时，

getAssets()方法将起作用。

如果在非Activity类中调用此方法，则需要从Context中调用此方法，该方法是从Activity类传递的。以下是您可以访问该方法的行。

ContextInstance.getAssets();

ContextInstance可以作为Activity类传递。

Answer 7

以下是一种读取资产中文件的方法：

/**
 * 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;
}

Answer 8

读取和写入文件总是冗长且容易出错。避免这些答案，只需使用Okio代替：

InputStream input = context.getAssets().open("helloworld.txt");
BufferedSource source = Okio.buffer(Okio.source(input));
String text = source.readByteString().string(Charset.forName("utf-8"));

Answer 9

在MainActivity.java中

@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);
}

Answer 10

您可以从文件中加载内容。考虑该文件存在于资产文件夹中。

public static InputStream loadInputStreamFromAssetFile(Context context, String fileName){
    AssetManager am = context.getAssets();
    try {
        InputStream is = am.open(fileName);
        return is;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

public static String loadContentFromFile(Context context, String path){
    String content = null;
    try {
        InputStream is = loadInputStreamFromAssetFile(context, path);
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        content = new String(buffer, "UTF-8");
    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return content;
}

现在，您可以通过调用以下函数来获取内容

String json= FileUtil.loadContentFromFile(context, "data.json");

考虑到data.json存储在Application \ app \ src \ main \ assets \ data.json

Answer 11

也许为时已晚，但是为了其他寻求桃花心水答案的人：

public static String loadAssetFile(Context context, String fileName) {
    try {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(context.getAssets().open(fileName)));
        StringBuilder out= new StringBuilder();
        String eachline = bufferedReader.readLine();
        while (eachline != null) {
            out.append(eachline);
            eachline = bufferedReader.readLine();
        }
        return out.toString();
    } catch (IOException e) {
        Log.e("Load Asset File",e.toString());
    }
    return null;
}

Answer 12

针对Kotlin的一线解决方案：

fun readFileText(fileName: String): String {
    return assets.open(fileName).bufferedReader().use { it.readText() }
}

Answer 13

使用Kotlin，您可以执行以下操作从Android中的资源中读取文件：

try {
    val inputStream:InputStream = assets.open("helloworld.txt")
    val inputString = inputStream.bufferedReader().use{it.readText()}
    Log.d(TAG,inputString)
} catch (e:Exception){
    Log.d(TAG, e.toString())
}

Answer 14

如果你使用除Activity以外的任何其他类，你可能想要这样做，

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader( YourApplication.getInstance().getAssets().open("text.txt"), "UTF-8"));

Answer 15

这是一种为InputStream文件夹中的文件获取assets而不使用Context，Activity，Fragment或{{1} }。如何从Application获取数据取决于您。这里的其他答案中有很多建议。

科特林

InputStream

Java

val is = ClassLoader::class.java.classLoader.getResourceAsStream("assets/your_file.ext")

如果正在使用自定义InputStream is = ClassLoader.class.getClassLoader().getResourceAsStream("assets/your_file.ext");，则所有投注都将关闭。

Answer 16

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 + "";

    }

Answer 17

@HpTerm回答Kotlin版本：

private fun getDataFromAssets(): String? {

    var bufferedReader: BufferedReader? = null
    var data: String? = null

    try {
        bufferedReader = BufferedReader(
            InputStreamReader(
                activity?.assets?.open("Your_FILE.html"),     
                "UTF-8"
            )
        )                  //use assets? directly if in activity

       var mLine:String = bufferedReader?.readLine()
        while (mLine != null) {
            data+= mLine
            mLine=bufferedReader.readLine()
        }

    } catch (e: Exception) {
        e.printStackTrace()
    } finally {
        try {
            bufferedReader?.close()
        } catch (e: Exception) {
           e.printStackTrace()
        }
    }
    return data
}

Answer 18

Scanner类可以简化此过程。

        StringBuilder sb=new StringBuilder();
        Scanner scanner=null;
        try {
            scanner=new Scanner(getAssets().open("text.txt"));
            while(scanner.hasNextLine()){
                sb.append(scanner.nextLine());
                sb.append('\n');
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(scanner!=null){try{scanner.close();}catch (Exception e){}}
        }
        mTextView.setText(sb.toString());

从资产中读取文件

18 个答案: