Simple database: Difference between revisions

=={{header|Java}}==

{{trans|D}}

{{works with|Java 7}}

<lang java>import java.io.*;

import java.text.*;

import java.util.*;

public class SimpleDatabase {

final static String filename = "simdb.csv";

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

if (args.length < 1 || args.length > 3) {

printUsage();

return;

}

switch (args[0].toLowerCase()) {

case "add":

addItem(args);

break;

case "latest":

printLatest(args);

break;

case "all":

printAll();

break;

default:

printUsage();

break;

}

}

private static class Item implements Comparable<Item>{

final String name;

final String date;

final String category;

Item(String n, String d, String c) {

name = n;

date = d;

category = c;

}

@Override

public int compareTo(Item item){

return item.date.compareTo(date);

}

@Override

public String toString() {

return String.format("%s,%s,%s%n", name, date, category);

}

}

private static void addItem(String[] input) {

if (input.length < 2) {

printUsage();

return;

}

List<Item> db = load();

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

String date = sdf.format(new Date());

String cat = (input.length == 3) ? input[2] : "none";

db.add(new Item(input[1], date, cat));

store(db);

}

private static void printLatest(String[] a) {

List<Item> db = load();

if (db.isEmpty()) {

System.out.println("No entries in database.");

return;

}

Collections.sort(db);

if (a.length == 2) {

for (Item item : db)

if (item.category.equals(a[1]))

System.out.println(item);

} else {

System.out.println(db.get(0));

}

}

private static void printAll() {

List<Item> db = load();

if (db.isEmpty()) {

System.out.println("No entries in database.");

return;

}

Collections.sort(db);

for (Item item : db)

System.out.println(item);

}

private static List<Item> load() {

List<Item> db = new ArrayList<>();

try (BufferedReader br = new BufferedReader(new FileReader(filename))) {

String line;

while ((line = br.readLine()) != null) {

String[] item = line.split(",");

db.add(new Item(item[0], item[1], item[2]));

}

} catch (IOException e) {

System.out.println(e);

}

return db;

}

private static void store(List<Item> db) {

try (FileWriter fw = new FileWriter(filename)) {

for (Item item : db)

fw.write(item.toString());

} catch (IOException e) {

System.out.println(e);

}

}

private static void printUsage() {

System.out.println("Usage:");

System.out.println(" simdb cmd [categoryName]");

System.out.println(" add add item, followed by optional category");

System.out.println(" latest print last added item(s), followed by "

+ "optional category");

System.out.println(" all print all");

System.out.println(" For instance: add \"some item name\" "

+ "\"some category name\"");

}

}</lang>

Output:

<pre>

C:\temp>java -jar SimpleDatabase.jar add item1

C:\temp>java -jar SimpleDatabase.jar add item2

C:\temp>java -jar SimpleDatabase.jar add item3 cat3

C:\temp>java -jar SimpleDatabase.jar add item4 cat3

C:\temp>java -jar SimpleDatabase.jar add item5 cat3

C:\temp>java -jar SimpleDatabase.jar latest

item1,2014-06-03 19:30:05,none

C:\temp>java -jar SimpleDatabase.jar latest cat3

item5,2014-06-03 19:30:23,cat3

item4,2014-06-03 19:30:20,cat3

item3,2014-06-03 19:30:14,cat3

C:\temp>java -jar SimpleDatabase.jar all

item5,2014-06-03 19:30:23,cat3

item4,2014-06-03 19:30:20,cat3

item3,2014-06-03 19:30:14,cat3

item2,2014-06-03 19:30:08,none

item1,2014-06-03 19:30:05,none</pre>