从文本文档中存储字符串并将其打印到屏幕

Question

So I have this code so far:

import java.util.*;
import java.io.*;

public class EmailMerge {

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

        Scanner templateReader = null;
        Scanner peopleReader = null;

        PrintWriter out = null;

        String template = "";
        ArrayList people = new ArrayList();

        try {

            templateReader = new Scanner(new FileInputStream("template.txt"));
            peopleReader = new Scanner(new FileInputStream("people.txt"));

            while(templateReader.hasNext()) {
                //System.out.print(templateReader.next());
                template = templateReader.next();
            }

            System.out.println(template);
        }
        catch(FileNotFoundException e)
        {
            System.out.println("File(s) not found...");
            System.exit(0);
        }
    }
}

I have a text document called template.txt that contains this:

Dear <<N>>,

Because you are <<A>> years old and <<G>>, we have a
free gift for you. You have absolutely nothing to buy;
just pay the shipping and handling charge of $9.99. To
claim your gift, call us immediately.
Thank you,

Office of Claims Department

and I have another text document called people.txt that contains names and ages of people like so:

John, 38, Male
Mary, 22, Female
so on and so forth...

What I have to do is go through all the names on the list and make a personalized message using the template. Then I have to save each to a unique text document(ie John.txt). What I want to do is store the names on the list into an ArrayList, I called people, and then store the template into a string, which I called template.

However, my issue comes in when I try to print out the template. I can't tell if I am storing it wrong of if there is a better way to print it out, but when I use this code I just get "Department" printed to the screen. I need to have the whole thing stored in the String template and be able to print it to the screen in its proper format like it is above. Please Help, Thanks A Bunch!!

UPDATE: Thank you guys so much for the help! One more question. I am finally at the end of the project and I have stored all of the necessary information into a few ArrayLists, however when I try to print out the template it will work, but it does it about a 1000 times. Here is the loop I am using:

for(int j = 0; j < people.size(); j++){
    for(int i = 0; i < names.size(); i++){
        System.out.println(template.replace("<<N>>", names.get(i)).replace("<<A>>", ages.get(i)).replace("<<G>>", genders.get(i)));
    }
}

I stored all of the names/ages/genders into the appropriate ArrayList. Thanks again!

Answer 1

You're replacing the template String variable each time instead of updating it (appending). Try the code below:

template += templateReader.next();

Or better - as stated by Luiggi in the comment - a StringBuilder :

StringBuiler builder = new StringBuilder("");
while(templateReader.hasNext()) {
        //System.out.print(templateReader.next());
        builder.append(templateReader.next());
}
template = builder.toString();

StringBuffer offers better performance than the + operator, so whenever you append Strings in a loop - like in this example - it's better to use it.

Answer 2

Use a StringBuilder to save the whole template in a String :

StringBuilder sb = new StringBuilder();
while(templateReader.hasNext()){
    //System.out.print(templateReader.next());
    sb.append(templateReader.next());
}
template = sb.toString();

It is faster than String concatenation especially if your template is long.

Answer 3

You can read the template.txt all at once using

String template = new Scanner(new File("template.txt")).useDelimiter("\\Z").next();
    System.out.println(template);

useDelimiter("\\Z") is used to read whole file at once.

Answer 4

I suggest breaking this into small parts that are each implemented as a separate method:

• One method to read in the file with the names and other data
• One method to read in the template
• One method to replace the "fields" in the template with the correct data

Designing your code this way will allow you to test each piece individually and make it easier to track down logic errors.