使用Java中的indexOf（）方法解析文件

Question

After verifing this post in stackoverflow I am using indexOf() method to parse values from file. Below is the format of my file-

10/05/2005 10:02;AM;a@xyz.com;student=student1 std=X marks=87 rollnumber=102
10/05/2005 10:05;AM;b@xyz.com;student=student2 std=IX rollnumber=26
10/05/2005 10:15;PM;c@xyz.com;student=student3 std=VII marks=87 attandance=5 rollnumber=12
10/05/2005 10:32;AM;d@xyz.com;student=student4 std=V marks=87 rollnumber=69

Note:The domain name ie xyz.com in email is not going to be changed in anywhere.
Below is the code snippet i am using currently-

            FileInputStream fis = new FileInputStream(file);
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    fis));

            String line = "";
            while ((line = br.readLine()) != null) {

                int index = -1;

                if ((index = line.indexOf("xyz.com")) != -1) {
                    int inStudent = line.indexOf("student=", index);
                    int spaceExistsinStudent = -1;
                    int studentIndex = -1;

                    if ((spaceExistsinStudent = line.indexOf("student=\"", inStudent)) != -1)
                        studentIndex = line.indexOf(" ", inStudent);
                    else
                        studentIndex = line.indexOf("\" ", spaceExistsinStudent);

                    int inSTD = line.indexOf("std=", studentIndex);
                    int spaceExistsinSTD = -1;
                    int stdIndex = -1;

                    if ((spaceExistsinSTD = line.indexOf("std=\"", inSTD)) != -1)
                        stdIndex = line.indexOf(" ", inSTD);
                    else
                        stdIndex = line.indexOf("\" ", spaceExistsinSTD);

                    String studentName = line.substring(inStudent + 9, studentIndex);
                    String stdName = line.substring(inSTD + 4, stdIndex);

There is no need to paste the entire code.
Well, using the above implementation, i am able to work, but is this effective solution as performace is considered? Any better way for achiveing the same....
Thank you in advance.

Answer 1

Instead of indexOf(), i would suggest StringTokenizer. basically you can split you String based on some separator (eg: ;)..

Example inside your while loop

        StringTokenizer st = new StringTokenizer(line,";");


        st.nextToken(); //Date
        st.nextToken(); //AM
        String email = st.nextToken();
        String values = st.nextToken();

        StringTokenizer st2 = new StringTokenizer(values," ");


        while (st2.hasMoreElements()) {
            String token = (String) st2.nextElement();
            if(token.startsWith("student=")){
                System.out.println(token.substring("student=".length()));
            }else if(token.startsWith("std=")){
                System.out.println(token.substring("std=".length()));
            }

        }

Answer 2

You don't need to use indexOf for everything. If you want to look at one character, you can use charAt() eg where you are checking for a '"'

I would use a method which extracts the value for a field to simplify the code.

Answer 3

As I stated in an earlier comment, I am surprised that the parsing is the bottleneck here. But if you wish to know other ways that you could do this, and just try them out and see which is the fastest, here are two more ideas that haven't been posted- using .split :

String[] arr1 = line.split(";");
String dateTime = arr1[0];
String ampm = arr1[1];
String email = arr1[2];
String[] arr2 = arr1[3].split(" ");
String student, std, marks, rollnumber;
student = std = marks = rollnumber = null;
for (String str : arr2) {
    String value = str.substring(str.indexOf("=") + 1);
    switch(str.charAt(2)) {
    case 'u': student = value; break;
    case 'd': std = value; break;
    case 'r': marks = value; break;
    case 'l': rollnumber = value; break;
    }
}

Or using a regex:

private static final Pattern PATTERN = Pattern.compile("([^;]+);([^;]+);([^;]+);student=([^ ]+) std=([^ ]+) marks=([^ ]+) rollnumber=([^ ]+)");

Matcher m = PATTERN.matcher(line);
m.find();
String dateTime = m.group(1);
String ampm = m.group(2);
String email = m.group(3);
String student = m.group(4);
String std = m.group(5);
String marks = m.group(6);
String rollnumber = m.group(7);