java - convert binary file to object

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
// Hint: the below solution uses custom deserialization approach,
//       the solution has very good performance.

import java.io.FileInputStream;
import java.io.IOException;
import java.io.DataInputStream;

public class Program {

    public static void main(String[] args) throws IOException
    {
        User user = new User();

        try (
            FileInputStream fileStream = new FileInputStream("user.dat");  // user.dat was saved using https://dirask.com/snippets/jmJm21
            DataInputStream dataStream = new DataInputStream(fileStream)
        ) {
            user.setId(dataStream.readLong());    // reads long
            user.setName(dataStream.readUTF());   // reads string
            user.setEmail(dataStream.readUTF());  // reads string
        }

        System.out.println("id:    " + user.getId());
        System.out.println("name:  " + user.getName());
        System.out.println("email: " + user.getEmail());
    }

    public static class User {

        private long id;
        private String name;
        private String email;

        public long getId() {
            return this.id;
        }

        public void setId(long id) {
            this.id = id;
        }

        public String getName() {
            return this.name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getEmail() {
            return this.email;
        }

        public void setEmail(String email) {
            this.email = email;
        }
    }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
// Hint: the below solution uses embedded deserialization mechanysm in Java.

import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;

public class Program {

	public static void main(String[] args) throws IOException, ClassNotFoundException {

        User user;

        try (
            FileInputStream fileStream = new FileInputStream("user.dat");  // user.dat was saved using https://dirask.com/snippets/jmJm21
            ObjectInputStream objectStream = new ObjectInputStream(fileStream)
        ) {
            user = (User) objectStream.readObject();
        }

        System.out.println("id:    " + user.getId());
        System.out.println("name:  " + user.getName());
        System.out.println("email: " + user.getEmail());
    }

    public static class User implements Serializable {

        private static final long serialVersionUID = 1833276496243006152L; // embedded random number is used to identify object type

	    private long id;
	    private String name;
	    private String email;

        public long getId() {
            return this.id;
        }

        public void setId(long id) {
            this.id = id;
        }

        public String getName() {
            return this.name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getEmail() {
            return this.email;
        }

        public void setEmail(String email) {
            this.email = email;
        }
    }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
// import java.io.FileInputStream;
// import java.io.IOException;
// import java.io.ObjectInputStream;
// import java.io.Serializable;

MyObject myObject;  // MyObject should have `private static final long serialVersionUID` filed.

try (
    FileInputStream fileStream = new FileInputStream("path/to/file.dat");  // path/to/file.dat was saved using https://dirask.com/snippets/jmJm21
    ObjectInputStream objectStream = new ObjectInputStream(fileStream)
) {
    myObject = (myObject) objectStream.readObject();
}