Java如何将文件中的字符串作为字节写入并取回字符串

Question

I need to write a string in a file as bytes in UTF-8 and then get these bytes back from file and convert it back to string and as a consiquence get the same string. May be it sounds easy but there is a hidden problem such as incorrect symbols in file. I mean that after appending in file it must contain something like:

00000008 d0bad0bb d18ed187 00000010 etc...

But it contains stuff like that:

mystring ---a lot of space--- (and the symbol that doesn't display here)

So, what have I already done? I've tried this way:

Before code read this: I keep strings in HashMap < String, String > that's why my code contains get(...) etc.

try {
        FileOutputStream oStream = new FileOutputStream("filename.txt");
        Set<String> keySet = storage.keySet();
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        for (String key : keySet) {
            byte[] keyInByte = key.getBytes("UTF-8");
            byte[] valueInByte = storage.get(key).getBytes("UTF-8");
            oStream.write(buffer.putInt(0, valueInByte.length).array());
            oStream.write(keyInByte);

            oStream.write((buffer.putInt(0, valueInByte.length).array()));
            oStream.write(valueInByte);
        }
    } catch (Exception e) {
        System.err.println("permission denied");
    }

I have also tried use PrintWriter, FileWriter, etc... but it doesn't give what I need. For example, some of them need toString() method but after toString() I will lose the ability to work with bytes.

! Notice, that I've tried to change my notepad to UTF-8 encode, but it gives no result.

Answer 1

If you want to use Properties you can do this.

new Properties(map).save(new FileOutputStream("filename.proeprties"));

to load the properties

Properties prop = new Properties();
prop.load(new FileInputStream("filename.properties"));
map.putAll(prop);

To save copying the data you can use Properties as a Map.

key1=value1
key2=value2

Note: a key cannot contain a = or a newline.

---

This is how I would do it in a binary format

DataOutputStream dos = new BufferedOutputStream(new FileOutputStream("filename.dat")));
dos.writeInt(map.size());
for (Map.Entry<String, String> entry : map.entrySet()) {
    dos.writeUTF(entry.getKey());
    dos.writeUTF(entry.getValue());
}
dos.close();

---

This is how I would write it in text, using UTF-8

PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOuputStream("filename.txt") "UTF-8"));
pw.println(map.size());
for (Map.Entry<String, String> entry : map.entrySet()) {
     pw.println(encode(entry.getKey()));
     pw.println(encode(entry.getValue()));
}
pw.close();


public static String encode(String s) {
    // if you can assume no new lines, don't do anything.
    return s.replaceAll("\\\\", "\\\\\\\\").replaceAll("\n", "\\\\n");
}

This will produce a like like

key1
value1
key2
value2

This you can edit fairly easy. If youc an assume the key doesn't have an = or : or tab, you can use one line like a properties file