java.util.Scanner读取具有不同字符编码的文件

Question

我使用Java读取文件列表。其中一些具有不同的编码，ANSI而不是UTF-8。java.util.Scanner无法读取这些文件并获取空的输出字符串。我尝试了另一种方法：

FileInputStream fis = new FileInputStream(my_file);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
InputStreamReader isr = new InputStreamReader(fis);
isr.getEncoding();

我不知道在ANSI的情况下如何更改字符编码。UTF-8和ANSI文件混合在同一个文件夹中。为此，我尝试使用Apache Tika。在我得到文件的编码后，我使用Scanner，但我得到了空输出。

Scanner scanner = new Scanner(my_file, detector.getCharset().toString());
line = scanner.nextLine();

Answer 1

有一个名为juniversalcardet的库，它可以帮助您猜测正确的编码。它最近更新，目前位于GitHub:上

https://github.com/albfernandez/juniversalchardet

然而，没有故障安全工具来检测编码，因为有很多未知的东西：

1. 这个文件是纯文本还是一些PNG
2. 它是否存储在(1，…，k，…，n(位编码中
3. 使用了哪种k位编码

一些猜测可以通过计算不常用的控制字符的数量来完成。当一个文件包含许多控制符号时，很可能是您选择了错误的编码。(然后试试下一个。(

Juniversalchardet尝试了多种更成功的方法来确定编码(甚至是中国编码(。它还提供了从已经选择正确编码的文件中打开读取器的方便方法：

(片段取自https://github.com/albfernandez/juniversalchardet#creating-a-reader(具有正确编码和自适应(

import org.mozilla.universalchardet.ReaderFactory;
import java.io.File;
import java.io.IOException;
import java.io.Reader;
public class TestCreateReaderFromFile {
public static void main (String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java TestCreateReaderFromFile FILENAME");
System.exit(1);
}
Reader reader = null;
try {
File file = new File(args[0]);
reader = ReaderFactory.createBufferedReader(file);
String line;
while((line=reader.readLine())!=null){
System.out.println(line); //Print each line to console
}
}
finally {
if (reader != null) {
reader.close();
}
}
}
}

编辑：添加扫描仪工厂

/*
(C) Copyright 2016-2017 Alberto Fernández <[e-mail]>
Adapted by Fritz Windisch 2018-11-15
The contents of this file are subject to the Mozilla Public License Version
1.1 (the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.mozilla.org/MPL/
Software distributed under the License is distributed on an "AS IS" basis,
WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
for the specific language governing rights and limitations under the
License.
Alternatively, the contents of this file may be used under the terms of
either the GNU General Public License Version 2 or later (the "GPL"), or
the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
in which case the provisions of the GPL or the LGPL are applicable instead
of those above. If you wish to allow use of your version of this file only
under the terms of either the GPL or the LGPL, and not to allow others to
use your version of this file under the terms of the MPL, indicate your
decision by deleting the provisions above and replace them with the notice
and other provisions required by the GPL or the LGPL. If you do not delete
the provisions above, a recipient may use your version of this file under
the terms of any one of the MPL, the GPL or the LGPL.
*/
import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Objects;
import java.util.Scanner;
import org.mozilla.universalchardet.UniversalDetector;
import org.mozilla.universalchardet.UnicodeBOMInputStream;
/**
* Create a scanner from a file with correct encoding
*/
public final class ScannerFactory {
private ScannerFactory() {
throw new AssertionError("No instances allowed");
}
/**
* Create a scanner from a file with correct encoding
* @param file The file to read from
* @param defaultCharset defaultCharset to use if can't be determined
* @return Scanner for the file with the correct encoding
* @throws java.io.IOException if some I/O error ocurrs
*/
public static Scanner createScanner(File file, Charset defaultCharset) throws IOException {
Charset cs = Objects.requireNonNull(defaultCharset, "defaultCharset must be not null");
String detectedEncoding = UniversalDetector.detectCharset(file);
if (detectedEncoding != null) {
cs = Charset.forName(detectedEncoding);
}
if (!cs.toString().contains("UTF")) {
return new Scanner(file, cs.name());
}
Path path = file.toPath();
return new Scanner(new UnicodeBOMInputStream(new BufferedInputStream(Files.newInputStream(path))), cs.name());
}
/**
* Create a scanner from a file with correct encoding. If charset cannot be determined,
* it uses the system default charset.
* @param file The file to read from
* @return Scanner for the file with the correct encoding
* @throws java.io.IOException if some I/O error ocurrs
*/
public static Scanner createScanner(File file) throws IOException {
return createScanner(file, Charset.defaultCharset());
}
}

Answer 2

您的方法不会给您正确的编码。

FileInputStream fis = new FileInputStream(my_file);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
InputStreamReader isr = new InputStreamReader(fis);
isr.getEncoding();

这将返回此InputStream使用的编码(读取javadoc(，而不是文件中写入的字符的编码(在您的情况下为my_file(。如果编码错误，扫描仪将无法正确读取文件。

事实上，如果我错了，一定要纠正我，没有办法100%准确地为特定文件使用编码。很少有项目在猜测编码方面有更好的成功率，但准确性不是100%。另一方面，如果你知道使用的编码，那么你可以使用读取文件

Scanner scanner = new Scanner(my_file, "charset");
scanner.nextLine();

此外，请找出在java for ANSI中使用的正确字符集名称。它要么是US-ASCII，要么是Cp1251。

无论你走哪条路，都要留意任何可能为你指明正确方向的IOException。

Answer 3

要使Scanner能够使用不同的编码，您必须向扫描仪的构造函数提供正确的编码。

要定义文件编码，最好使用外部lib(例如https://github.com/albfernandez/juniversalchardet)。但如果你确实知道可能的编码，你可以根据维基百科手动检查

public static void main(String... args) throws IOException {
List<String> lines = readLinesFromFile(new File("d:/utf8.txt"));
}
public static List<String> readLinesFromFile(File file) throws IOException {
try (Scanner scan = new Scanner(file, getCharsetName(file))) {
List<String> lines = new LinkedList<>();
while (scan.hasNext())
lines.add(scan.nextLine());
return lines;
}
}
private static String getCharsetName(File file) throws IOException {
try (InputStream in = new FileInputStream(file)) {
if (in.read() == 0xEF && in.read() == 0xBB && in.read() == 0xBF)
return StandardCharsets.UTF_8.name();
return StandardCharsets.US_ASCII.name();
}
}