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This noncompliant code example attempts to convert the byte array representing a BigInteger into a String. Because some of the bytes do not denote valid characters, the resulting String representation loses information. Converting the String back to a BigInteger produces a different value.
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BigInteger x = new BigInteger("530500452766");
// convert x to a String
byte[] byteArray = x.toByteArray();
String s = new String(byteArray);
// convert s back to a BigInteger
byteArray = s.getBytes();
x = new BigInteger(byteArray);
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This compliant solution first produces a String representation of the BigInteger object and then converts the String object to a byte array. This process is reversed on input. Because the textual representation in the String object was generated by the BigInteger class, it contains valid characters.
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BigInteger x = new BigInteger("530500452766");
String s = x.toString(); // valid character data
try {
byte[] byteArray = s.getBytes("UTF8");
// ns prints as "530500452766"
String ns = new String(byteArray, "UTF8");
// construct the original BigInteger
BigInteger x1 = new BigInteger(ns);
} catch (UnsupportedEncodingException ex) {
// handle error
}
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This noncompliant code example corrupts the data when string contains characters that are not representable in the specified charset.
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// Corrupts data on errors
public static byte[] toCodePage(String charset, String string)
throws UnsupportedEncodingException {
return string.getBytes(charset);
}
// Fails to detect corrupt data
public static String fromCodePage(String charset, byte[] bytes)
throws UnsupportedEncodingException {
return new String(bytes, charset);
}
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public static byte[] toCodePage(String charset, String string)
throws IOException {
Charset cs = Charset.forName(charset);
CharsetEncoder coder = cs.newEncoder();
ByteBuffer bytebuf = coder.encode(CharBuffer.wrap(string));
byte[] bytes = new byte[bytebuf.limit()];
bytebuf.get(bytes);
return bytes;
}
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// Corrupts data on errors
public static void toFile(String charset, String filename,
String string) throws IOException {
FileOutputStream stream = new FileOutputStream(filename, true);
OutputStreamWriter writer = new OutputStreamWriter(stream, charset);
writer.write(string, 0, string.length());
writer.close();
}
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public static void toFile(String filename, String string,
String charset) throws IOException {
Charset cs = Charset.forName(charset);
CharsetEncoder coder = cs.newEncoder();
FileOutputStream stream = new FileOutputStream(filename, true);
OutputStreamWriter writer = new OutputStreamWriter(stream, coder);
writer.write(string, 0, string.length());
writer.close();
}
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Use the FileInputStream and InputStreamReader objects to read back the data from the file. InputStreamReader accepts a optional CharsetDecoder argument, which must be the same as that previously used for writing to the file.
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