编码DataInputStream

Question

I need to encode my files in "ISO-8859-1". I know how to do this with a Reader like this:

BufferedReader br = new BufferedReader(new InputStreamReader(
            new FileInputStream(src), "ISO-8859-1"))

But I'm asking how to encode a DataInputStream like this.

My decleration right now:

DataInputStream dit = new DataInputStream(new BufferedInputStream(
            new FileInputStream(src)))

I would prefer a solution, where the encoding-parameter is in the decleration. The data I want to read has been written with a DataOutputStream.

Import-method and export-method for DataStreams:

public void importDST(String src) throws FileNotFoundException, IOException{
    try (DataInputStream dit = new DataInputStream(new BufferedInputStream(new FileInputStream(src)))) {
        while(dit.available() > 0) {
            pupils.add(new Pupil(dit.readInt(), dit.readInt(), dit.readUTF(), dit.readUTF(), dit.readChar(),
                    dit.readUTF(), dit.readInt(), dit.readInt(), dit.readInt(), dit.readUTF(), dit.readUTF(), dit.readUTF(), dit.readUTF(),
                    dit.readUTF(), dit.readUTF()));
        }
    } catch (FileNotFoundException e) {
        throw e;
    } catch (IOException e) {
        throw e;
    }
}

public void exportDST(String dest, ArrayList<Pupil> pupils) throws FileNotFoundException, IOException{
    this.pupils = pupils;
    try (DataOutputStream dot = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(dest)))) {
        for (Pupil p : this.pupils) {
            dot.writeInt(p.getId());
            dot.writeInt(p.getNumber());
            dot.writeUTF(p.getFirstname());
            dot.writeUTF(p.getLastname());
            dot.writeChar(p.getGender());
            dot.writeUTF(p.getReligion());
            dot.writeInt(p.getDay());
            dot.writeInt(p.getMonth());
            dot.writeInt(p.getYear());
            dot.writeUTF(p.getStreet());
            dot.writeUTF(p.getPlz());
            dot.writeUTF(p.getLocation());
            dot.writeUTF(p.getShortName());
            dot.writeUTF(p.getClassName());
            dot.writeUTF(p.getKvLastname());
        }
    } catch (FileNotFoundException e) {
        throw e;
    } catch (IOException e) {
        throw e;
    }
}

class Pupil:

public class Pupil implements Serializable{
private int id;
private int number;
private String firstname;
private String lastname;
private char gender;
private String religion;
private int day;
private int month;
private int year;
private String street;
private String plz;
private String location;
private String shortName;
private String className;
private String kvLastname;

public Pupil() {}

public Pupil(int id, int number, String firstname, String lastname, char gender,
             String religion, int day, int month, int year, String street, String plz, String location,
             String shortName, String className, String kvLastname) {
    this.id = id;
    this.number = number;
    this.firstname = firstname;
    this.lastname = lastname;
    this.gender = gender;
    this.religion = religion;
    this.day = day;
    this.month = month;
    this.year = year;
    this.street = street;
    this.plz = plz;
    this.location = location;
    this.shortName = shortName;
    this.className = className;
    this.kvLastname = kvLastname;
}
}

Answer 1

As for ObjectInputStream, the documentation states that

An ObjectInputStream deserializes primitive data and objects previously written using an ObjectOutputStream.

Also, note:

Only objects that support the java.io.Serializable or java.io.Externalizable interface can be read from streams.

That is, the read data has previously been serialized (or externalized) using ObjectOutputStream and given objects that implement Serializable (or Externalizable). You would thus deal with charset encoding for any String attributes in the readObject and `writeObject' methods of your Serializable objects.

As for DataInputStream, see this answer: DataInputStream and UTF-8

You would have to specify the encoding when creating a String from the read bytes.

• https://docs.oracle.com/javase/7/docs/api/java/io/ObjectInputStream.html
• https://docs.oracle.com/javase/7/docs/api/java/io/DataInputStream.html

Answer 2

Your question doesn't really make sense.

Streams model streams of bytes . They don't have a character encoding, they are just bytes.

Readers read streams of characters . These are ultimately streams of bytes too, but there is a character encoding which says how to convert those bytes to chars. As such, it makes sense to be able to specify this encoding in the constructor.

DataInputStream s are Stream s: they read a binary so they don't have a character encoding.

Answer 3

I bypassed this problem by writing and reading just Ints and Bytes, instead of Strings. I read bytearrays and made a new String with the encoding out of it. Here is the changed code:

Reading:

public void importDST(String src) throws IOException{
    try (DataInputStream dit = new DataInputStream(new BufferedInputStream(new FileInputStream(src)))) {
        while (dit.available() > 0) {
            Pupil p = new Pupil();
            byte[] arr;
            int len;

            p.setId(dit.readInt());
            p.setNumber(dit.readInt());
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setFirstname(new String(arr, "ISO-8859-1"));
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setLastname(new String(arr, "ISO-8859-1"));
            p.setGender(dit.readChar());
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setReligion(new String(arr, "ISO-8859-1"));
            p.setDay(dit.readInt());
            p.setMonth(dit.readInt());
            p.setYear(dit.readInt());
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setStreet(new String(arr, "ISO-8859-1"));
            p.setPlz(dit.readInt());
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setLocation(new String(arr, "ISO-8859-1"));
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setShortName(new String(arr, "ISO-8859-1"));
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setClassName(new String(arr, "ISO-8859-1"));
            len = dit.readInt();
            arr = new byte[len];
            dit.readFully(arr);
            p.setKvLastname(new String(arr, "ISO-8859-1"));

            pupils.add(p);
        }
    }
}

Writing:

public void exportDST(String dest, ArrayList<Pupil> pupils) throws IOException{
    this.pupils = pupils;
    try (DataOutputStream dot = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(dest)))) {
        for (Pupil p : pupils) {
            dot.writeInt(p.getId());
            dot.writeInt(p.getNumber());
            dot.writeInt(p.getFirstname().length());
            dot.writeBytes(p.getFirstname());
            dot.writeInt(p.getLastname().length());
            dot.writeBytes(p.getLastname());
            dot.writeChar(p.getGender());
            dot.writeInt(p.getReligion().length());
            dot.writeBytes(p.getReligion());
            dot.writeInt(p.getDay());
            dot.writeInt(p.getMonth());
            dot.writeInt(p.getYear());
            dot.writeInt(p.getStreet().length());
            dot.writeBytes(p.getStreet());
            dot.writeInt(p.getPlz());
            dot.writeInt(p.getLocation().length());
            dot.writeBytes(p.getLocation());
            dot.writeInt(p.getShortName().length());
            dot.writeBytes(p.getShortName());
            dot.writeInt(p.getClassName().length());
            dot.writeBytes(p.getClassName());
            dot.writeInt(p.getKvLastname().length());
            dot.writeBytes(p.getKvLastname());
        }
    }
}

Thanks for all your responses!