以字符串形式读取文件

Question

我需要在 android 中将 xml 文件作为字符串加载，以便将其加载到 TBXML xml 解析器库并解析它。即使对于一些 KB 的非常小的 xml 文件，我现在必须以字符串形式读取文件的实现需要大约 2 秒。是否有任何已知的快速方法可以在 Java/Android 中将文件作为字符串读取？

---

这是我现在的代码：

public static String readFileAsString(String filePath) {
    String result = "";
    File file = new File(filePath);
    if ( file.exists() ) {
        //byte[] buffer = new byte[(int) new File(filePath).length()];
        FileInputStream fis = null;
        try {
            //f = new BufferedInputStream(new FileInputStream(filePath));
            //f.read(buffer);

            fis = new FileInputStream(file);
            char current;
            while (fis.available() > 0) {
                current = (char) fis.read();
                result = result + String.valueOf(current);
            }
        } catch (Exception e) {
            Log.d("TourGuide", e.toString());
        } finally {
            if (fis != null)
                try {
                    fis.close();
                } catch (IOException ignored) {
            }
        }
        //result = new String(buffer);
    }
    return result;
}

Answer 1

最终使用的代码如下：

http://www.java2s.com/Code/Java/File-Input-Output/ConvertInputStreamtoString.htm

public static String convertStreamToString(InputStream is) throws Exception {
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();
    String line = null;
    while ((line = reader.readLine()) != null) {
      sb.append(line).append("\n");
    }
    reader.close();
    return sb.toString();
}

public static String getStringFromFile (String filePath) throws Exception {
    File fl = new File(filePath);
    FileInputStream fin = new FileInputStream(fl);
    String ret = convertStreamToString(fin);
    //Make sure you close all streams.
    fin.close();        
    return ret;
}

Answer 2

您可以使用org.apache.commons.io.IOUtils.toString(InputStream is, Charset chs) 来执行此操作。

例如

IOUtils.toString(context.getResources().openRawResource(<your_resource_id>), StandardCharsets.UTF_8)

添加正确的库：

将以下内容添加到您的 app/build.gradle 文件中：

dependencies {
    compile 'org.apache.directory.studio:org.apache.commons.io:2.4'
}

• https://stackoverflow.com/a/33820307/1815624

对于 Maven 存储库，请参阅 -> this link

直接下载jar见->https://commons.apache.org/proper/commons-io/download_io.cgi

Answer 3

重做源自-> the accepted answer的方法集

@JaredRummler 对您的评论的回答：

Read file As String

这不会在字符串末尾添加一个额外的新行吗？

为防止在末尾添加换行符，您可以在第一个循环期间使用布尔值集，就像在代码示例 Boolean firstLine 中一样

public static String convertStreamToString(InputStream is) throws IOException {
   // http://www.java2s.com/Code/Java/File-Input-Output/ConvertInputStreamtoString.htm
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();
    String line = null;
    Boolean firstLine = true;
    while ((line = reader.readLine()) != null) {
        if(firstLine){
            sb.append(line);
            firstLine = false;
        } else {
            sb.append("\n").append(line);
        }
    }
    reader.close();
    return sb.toString();
}

public static String getStringFromFile (String filePath) throws IOException {
    File fl = new File(filePath);
    FileInputStream fin = new FileInputStream(fl);
    String ret = convertStreamToString(fin);
    //Make sure you close all streams.
    fin.close();
    return ret;
}

Answer 4

如果你使用 Kotlin，这很容易：

val textFile = File(cacheDir, "/text_file.txt")
val allText = textFile.readText()
println(allText)

来自readText() 文档：

使用 UTF-8 或字符串获取此文件的全部内容 指定的字符集。不建议在大文件上使用此方法。它 文件大小的内部限制为 2 GB。

Answer 5

我们事先知道文件的大小，所以只需一次阅读！

String result;
File file = ...;

long length = file.length();
if (length < 1 || length > Integer.MAX_VALUE) {
    result = "";
    Log.w(TAG, "File is empty or huge: " + file);
} else {
    try (FileReader in = new FileReader(file)) {
        char[] content = new char[(int)length];

        int numRead = in.read(content);
        if (numRead != length) {
            Log.e(TAG, "Incomplete read of " + file + ". Read chars " + numRead + " of " + length);
        }
        result = new String(content, 0, numRead);
    }
    catch (Exception ex) {
        Log.e(TAG, "Failure reading " + this.file, ex);
        result = "";
    }
}

Answer 6

public static String readFileToString(String filePath) {
    InputStream in = Test.class.getResourceAsStream(filePath);//filePath="/com/myproject/Sample.xml"
    try {
        return IOUtils.toString(in, StandardCharsets.UTF_8);
    } catch (IOException e) {
        logger.error("Failed to read the xml : ", e);
    }
    return null;
}

Answer 7

这对我有用

i use this path

String FILENAME_PATH =  "/mnt/sdcard/Download/Version";

public static String getStringFromFile (String filePath) throws Exception {
    File fl = new File(filePath);
    FileInputStream fin = new FileInputStream(fl);
    String ret = convertStreamToString(fin);
    //Make sure you close all streams.
    fin.close();        
    return ret;

}