commit 6276b54cb10ad447672d8733a155a7ec631cc8af
Author: alexandrawerner <alexandrawerner@alexandrawerner.local>
Date:   Wed Mar 25 15:10:04 2026 +0100

    added java backend (logic only)

diff --git a/UrlShortener.java b/UrlShortener.java
new file mode 100644
index 0000000..e283922
--- /dev/null
+++ b/UrlShortener.java
@@ -0,0 +1,146 @@
+package backendAlex;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import java.security.SecureRandom;
+import java.util.HashSet;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class UrlShortener {
+    private Path file = Paths.get("/Users/alexandrawerner/project/urlShortenerTest/data.json");
+    private List<UrlShortenerData> urlData;
+
+    private String linkPrefix = "https://bolt-link.de/";  //https://shorturl.at/RDKwO
+    private static final String CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+    private static final int CODE_LENGTH = 6;
+    private static final SecureRandom random = new SecureRandom();
+
+    public String getShortUrl(String longUrl){
+        readJson();
+        boolean newUrl = true;
+        String shortUrl = new String();
+        for (UrlShortenerData url : urlData) {
+            if(url.getLongUrl().equals(longUrl)){
+                shortUrl = url.getShortUrl();
+                newUrl = false;
+                break;
+            }
+        }
+        if(newUrl){
+            shortUrl = createShortUrl();
+            setNewUrl(shortUrl, longUrl);
+        }
+        return shortUrl;
+    }
+
+    public String getLongUrl(String shortUrl){
+        readJson();
+        String longUrl = "url not found";
+        for (UrlShortenerData url : urlData) {
+            if(url.getLongUrl().equals(shortUrl)){
+                longUrl = url.getShortUrl();
+            }
+        }
+        return longUrl;
+    }
+
+    private String createShortUrl(){
+        String url = linkPrefix + generateUniqueCode();
+        return url;
+    }
+
+    private String generateUniqueCode() {
+        HashSet<String> usedCodes = new HashSet<>();
+        usedCodes = getAllLinkSuffix();
+
+        String code;
+        do {
+            code = generateRandomCode();
+        } while (usedCodes.contains(code)); // Check if already used //TODO mit equals checken und nicht mir contains
+        
+        usedCodes.add(code);
+        return code;
+    }
+    
+    private String generateRandomCode() {
+        StringBuilder sb = new StringBuilder(CODE_LENGTH);
+        
+        for (int i = 0; i < CODE_LENGTH; i++) {
+            int index = random.nextInt(CHARACTERS.length());
+            sb.append(CHARACTERS.charAt(index));
+        }
+        
+        return sb.toString();
+    }
+
+    private HashSet<String> getAllLinkSuffix() {
+    readJson();
+    HashSet<String> usedCodes = new HashSet<>();
+    
+    for (UrlShortenerData url : urlData) {
+        String shortUrl = url.getShortUrl();
+        try{
+            URI uri = new URI(shortUrl);
+            
+            String path = uri.getPath();
+
+            if (path.contains("/")) {
+                usedCodes.add(path.substring(path.lastIndexOf('/') + 1));
+            }
+        }catch(URISyntaxException e){
+            e.printStackTrace();
+        }
+    }
+    return usedCodes; 
+    }
+
+    private void setNewUrl(String shortUrl, String longUrl){
+        readJson();
+        UrlShortenerData newUrl = new UrlShortenerData(longUrl, shortUrl);
+        urlData.add(newUrl);
+        writeJson();
+    }
+
+    private void readJson(){
+        try {
+            String contentWithCharset = Files.readString(file, StandardCharsets.UTF_8);
+            ObjectMapper mapper = new ObjectMapper();
+            urlData  = mapper.readValue(contentWithCharset, new TypeReference<List<UrlShortenerData>>(){});
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private void writeJson(){
+        try{
+            ObjectMapper mapper = new ObjectMapper();
+            // Liste -> JSON Array
+            String jsonString = mapper.writeValueAsString(urlData);
+            Files.writeString(file, jsonString);       
+        }catch(IOException e){
+            e.printStackTrace();
+        }
+    }
+
+    //test function
+    public void printJson(){
+        readJson();
+        ObjectMapper mapper = new ObjectMapper();
+        try{
+        String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(urlData);
+        System.out.println(prettyJson);
+        }catch(JsonProcessingException e){
+            e.printStackTrace();
+            System.out.println(e);
+        }
+    }
+}
diff --git a/UrlShortenerData.java b/UrlShortenerData.java
new file mode 100644
index 0000000..3b0db65
--- /dev/null
+++ b/UrlShortenerData.java
@@ -0,0 +1,38 @@
+package backendAlex;
+
+
+public class UrlShortenerData {
+
+    private String longUrl;
+
+    private String shortUrl;
+    
+    // Default constructor (required for Jackson)
+    public UrlShortenerData() {
+    }
+    
+    // Optional: Convenience constructor
+    public UrlShortenerData(String longUrl, String shortUrl) {
+        this.longUrl = longUrl;
+        this.shortUrl = shortUrl;
+    }
+    
+    // Standard Setter für longUrl
+    public void setLongUrl(String longUrl) {
+        this.longUrl = longUrl;
+    }
+    
+    // Standard Setter für shortUrl
+    public void setShortUrl(String shortUrl) {
+        this.shortUrl = shortUrl;
+    }
+    
+    // Getter
+    public String getLongUrl() {
+        return this.longUrl;
+    }
+    
+    public String getShortUrl() {
+        return this.shortUrl;
+    }
+}
\ No newline at end of file
diff --git a/test.java b/test.java
new file mode 100644
index 0000000..5c5f786
--- /dev/null
+++ b/test.java
@@ -0,0 +1,17 @@
+package backendAlex;
+
+class test {
+    public static void main(String[] args) {
+        UrlShortener url = new UrlShortener();
+        //String shortUrl = url.getShortUrl("longUrlTest2");
+        //System.out.println(shortUrl);
+
+        //String longUrl = url.getLongUrl(shortUrlTest3);
+        //System.out.println(longUrl);
+        String shortUrl = url.getShortUrl("longUrlTest6");
+        System.out.println(shortUrl);
+
+        //url.printJson();
+    }
+    
+}