how Mark used simple scripts to download the entire catalog of student directory posts. I will show you how to do the same in Java.
Requirements:
- A text editor (Notepad or Notepad++ will do)
- A Mac with Terminal
- Basic Java knowledge
Procedure
How this program will work is it will basically be for downloading a large succession of images from a database. The database will often have a template such as www.example.com/folderone/foldertwo/folderthree/J8031736345854221.JPG, with the next picture being J8031736345854222.JPG. The program will increment the last digit by 1 through a specified range.
Step 1:
First, in the Java editor, we add the basic configuration code to a file you created titled "Main.java":
import java.lang.Runtime;
import java.io.IOException;
import javax.swing.JOptionPane;
import java.lang.Integer;
import java.lang.String;
public class Main {
public static void main(String[] args) {
}
}
You should probably be able to tell the classes we will be using.
Step 2:
Let's say we want www.example.com/folderone/foldertwo/folderthree/J8031736345854221.JPG through www.example.com/folderone/foldertwo/folderthree/J8031736345854353.JPG
Now, we display three dialogue boxes asking for a string. Basically, the first box will take in the left unchanging part of the URL (www.example.com/folderone/foldertwo/folderthree/J8031736345854, for example), the second asking for the range of the variable part (221-353), and the last asking for the unchanging ending (.JPG).
String firstURL = JOptionPane
.showInputDialog(null,
"Enter the first part of the static URL",
"http://www.example.com/firstFolder/SecondFolder/firstpartoffiles");
String secondURL = JOptionPane.showInputDialog(null,
"Enter the variable part of the URL in a range", "x-y");
String thirdURL = JOptionPane.showInputDialog(null,
"Enter the first part of the static URL", ".jpg");
Step 3:
Now, we need to split the range into an array of values at the dash
String[] range = secondURL.split("-");
Step 4:
Finally, we need to add a loop downloading the image using the Unix wget command, then update the changing part, then download it again (we also add some logs to the terminal for fun):
for (int i = Integer.parseInt(range[0]); i <= Integer.parseInt(range[1]); i++) {
try {
System.out.println("wget " + firstURL + i + thirdURL);
Process p = r.exec("wget "+ firstURL + i + thirdURL);
} catch (IOException e) {
e.printStackTrace();
}
Reconciliation:
If you were following along so far, you're code should look like this:
import java.lang.Runtime;
import java.io.IOException;
import javax.swing.JOptionPane;
import java.lang.Integer;
import java.lang.String;
public class Main {
public static void main(String[] args) {
String firstURL = JOptionPane
.showInputDialog(null,
"Enter the first part of the static URL",
"http://www.example.com/firstFolder/SecondFolder/firstpartoffiles");
String secondURL = JOptionPane.showInputDialog(null,
"Enter the variable part of the URL in a range", "x-y");
String thirdURL = JOptionPane.showInputDialog(null,
"Enter the first part of the static URL", ".jpg");
String[] range = secondURL.split("-");
Runtime r = Runtime.getRuntime();
for (int i = Integer.parseInt(range[0]); i <= Integer.parseInt(range[1]); i++) {
try {
System.out.println("wget " + firstURL + i + thirdURL);
Process p = r.exec("wget "+ firstURL + i + thirdURL);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Running the application
Move the Java file (Main.java) into the folder you wish to download the images into.
Now open Terminal and type to navigate to the file location:
cd (then the directory you placed Main.java into)
Now, compile the program by typing:
javac Main.java
Finally, run the program by typing:
java Main
Now, just enter in the information into the dialogue boxes, in the range one separating your values by a hyphen. Once in process, the System.out.println statement kicks in, printing the web addresses of each downloaded image so you can see that everything is working all right.
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