Allow to specify the @file charset

doc/index.html

@@ -525,6 +525,10 @@ <h2><a class="section" name="Syntax">@ syntax</a></h2>
 java Main @/tmp/parameters
 </pre>
 
+<p>The file is read using the default charset unless <code>JCommander#setAtFileCharset</code> had been called.</p>
+
+<p>Ths feature can be disabled by calling <code>JCommander#setExpandAtSign</code>.</p>
+
 <h2><a class="section" name="Arities">Arities (multiple values for parameters)</a></h2>
 
 <h3><a class="section" name="fixed-arities" indent="..">Fixed arities</a></h3>

src/main/java/com/beust/jcommander/JCommander.java

@@ -19,13 +19,15 @@
 package com.beust.jcommander;
 
 import java.io.BufferedReader;
-import java.io.FileReader;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -171,6 +173,7 @@ public int compare(ParameterDescription p0, ParameterDescription p1) {
      * The factories used to look up string converters.
      */
     private final List<IStringConverterInstanceFactory> m_converterInstanceFactories = new CopyOnWriteArrayList<>();
+    private Charset m_atFileCharset = Charset.defaultCharset();
   }
 
   private JCommander(Options options) {
@@ -224,6 +227,12 @@ public JCommander(Object object, String... args) {
     parse(args);
   }
 
+  /**
+   * Disables expanding {@code @file}.
+   *
+   * JCommander supports the {@code @file} syntax, which allows you to put all your options into a file and pass this file as parameter
+   * @param expandAtSign whether to expand {@code @file}.
+   */
   public void setExpandAtSign(boolean expandAtSign){
     options.expandAtSign = expandAtSign;
   }
@@ -484,23 +493,18 @@ private String getOptionPrefixes(String arg) {
    * @param fileName the command line filename
    * @return the file content as a string.
    */
-  private static List<String> readFile(String fileName) {
+  private List<String> readFile(String fileName) {
     List<String> result = Lists.newArrayList();
 
-    try {
-      BufferedReader bufRead = new BufferedReader(new FileReader(fileName));
-
+    try (BufferedReader bufRead = Files.newBufferedReader(Paths.get(fileName), options.m_atFileCharset)) {
       String line;
-
       // Read through file one line at time. Print line # and line
       while ((line = bufRead.readLine()) != null) {
         // Allow empty lines and # comments in these at files
         if (line.length() > 0 && ! line.trim().startsWith("#")) {
             result.add(line);
         }
       }
-
-      bufRead.close();
     }
     catch (IOException e) {
       throw new ParameterException("Could not read file " + fileName + ": " + e);
@@ -1647,8 +1651,14 @@ public void setAllowParameterOverwriting(boolean b) {
   public boolean isParameterOverwritingAllowed() {
     return options.m_allowParameterOverwriting;
   }
-//  public void setCaseSensitiveCommands(boolean b) {
-//    m_caseSensitiveCommands = b;
-//  }
+
+  /**
+   * Sets the charset used to expand {@code @files}.
+   * @param charset the charset
+   */
+  public void setAtFileCharset(Charset charset) {
+    options.m_atFileCharset = charset;
+  }
+
 }
 

src/test/java/com/beust/jcommander/JCommanderTest.java

@@ -20,10 +20,13 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.File;
+import java.io.FileOutputStream;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStreamWriter;
 import java.math.BigDecimal;
+import java.nio.charset.Charset;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
@@ -644,6 +647,29 @@ public void atFileCanContainEmptyLines() throws IOException {
     new JCommander(new Args1(), "@" + f.getAbsolutePath());
   }
 
+  public void atFileWithInNonDefaultCharset() throws IOException {
+    final Charset utf32 = Charset.forName("UTF-32");
+    final File f = File.createTempFile("JCommander", null);
+    f.deleteOnExit();
+    try (OutputStreamWriter fw = new OutputStreamWriter(new FileOutputStream(f), utf32)) {
+      fw.write("-log\n");
+      fw.write("2\n");
+      fw.write("-groups\n");
+      fw.write("\u9731\n");
+    }
+    final Args1 args1 = new Args1();
+    final JCommander jc = new JCommander(args1);
+    try {
+      jc.parse("@" + f.getAbsolutePath());
+      throw new IllegalStateException("Expected exception to be thrown");
+    } catch (ParameterException expected) {
+      Assert.assertTrue(expected.getMessage().startsWith("Could not read file"));
+    }
+    jc.setAtFileCharset(utf32);
+    jc.parse("@" + f.getAbsolutePath());
+    Assert.assertEquals("\u9731", args1.groups);
+  }
+
   public void handleEqualSigns() {
     ArgsEquals a = new ArgsEquals();
     JCommander jc = new JCommander(a);