diff --git a/src/main/java/de/hsel/itech/db/Database.java b/src/main/java/de/hsel/itech/db/Database.java
index 146d2a6..9ea4650 100644
--- a/src/main/java/de/hsel/itech/db/Database.java
+++ b/src/main/java/de/hsel/itech/db/Database.java
@@ -300,6 +300,7 @@ public class Database {
         Map.Entry<ResultSet, Connection> entry = getResultSet(id, book);
         assert entry != null;
 
+
         ResultSet rs = entry.getKey();
         Book book = null;
         try {
diff --git a/src/main/java/de/hsel/itech/servlet/AddBook.java b/src/main/java/de/hsel/itech/servlet/AddBook.java
index e50e7c0..a53e4d5 100644
--- a/src/main/java/de/hsel/itech/servlet/AddBook.java
+++ b/src/main/java/de/hsel/itech/servlet/AddBook.java
@@ -6,6 +6,14 @@ import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.io.PrintWriter;
 
+/**
+ * Servlet: form to add a book to the database
+ *
+ *
+ * @author Julian Hinxlage
+ * @version 0.1
+ * @since 0.1
+ */
 public class AddBook extends HttpServlet {
 
 
@@ -18,20 +26,19 @@ public class AddBook extends HttpServlet {
         Utillity.insertFile(out, "template_head.html");
 
         out.println("<form class=\"m-container\" action=\"booklist\" method=post>");
-        Utillity.addInput(out, "ISBN", "isbn");
+        Utillity.addValidationInput(out, "ISBN", "isbn", "text", "0", "[0-9]*");
         Utillity.addInput(out,"Titel", "title");
         Utillity.addInput(out,"Author", "author");
-        Utillity.addInput(out,"Preis", "price", "0");
-        Utillity.addInput(out,"Jahr", "year", "2019");
+        Utillity.addValidationInput(out,"Preis", "price", "text", "0", "[0-9]*(,[0-9]{1,2})?");
+        Utillity.addValidationInput(out,"Jahr", "year", "text", "2019", "[0-9]*");
         Utillity.addInput(out,"Beschreibung", "description");
         Utillity.addInput(out,"Verlag", "publisher");
         Utillity.addInput(out,"Kategorie", "category");
         Utillity.addInput(out,"Bild", "image", "DxAzOKSiPoE");
-        Utillity.addTypeButton(out, "Hinzufügen", "submit");
+        Utillity.addSubmitButton(out, "Hinzufügen");
         out.println("</form>");
 
 
-        //Utillity.addButton(out,"Hinzufügen", "/itech/booklist");
         Utillity.addButton(out,"Zurück zur Buchliste", "booklist");
 
         Utillity.insertFile(out, "template_footer.html");
diff --git a/src/main/java/de/hsel/itech/servlet/BookList.java b/src/main/java/de/hsel/itech/servlet/BookList.java
index c7ef4f7..bacbf33 100644
--- a/src/main/java/de/hsel/itech/servlet/BookList.java
+++ b/src/main/java/de/hsel/itech/servlet/BookList.java
@@ -16,6 +16,14 @@ import java.time.Year;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Servlet: list of all books and remove function
+ *
+ *
+ * @author Julian Hinxlage
+ * @version 0.1
+ * @since 0.1
+ */
 public class BookList extends HttpServlet {
 
     protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
@@ -25,12 +33,11 @@ public class BookList extends HttpServlet {
         //get database object
         Database db = Database.getInstance();
 
-        //print parameters (debug)
-        /*Enumeration<String> names = req.getParameterNames();
-        while (names.hasMoreElements()) {
-            String name = names.nextElement();
-            System.out.println(name + "=" + req.getParameter(name));
-        }*/
+        resp.setCharacterEncoding("utf-8");
+        PrintWriter out = resp.getWriter();
+
+        //header template
+        Utillity.insertFile(out, "template_head.html");
 
         //remove book by id
         String param = req.getParameter("removeid");
@@ -40,45 +47,76 @@ public class BookList extends HttpServlet {
             resp.sendRedirect("booklist");
         }
 
+        //add book to database
         if (req.getParameter("title") != null) {
-            long isbn = Long.parseLong(req.getParameter("isbn"));
-            String title = req.getParameter("title");
-            String authorName = req.getParameter("author");
-            int price = Integer.parseInt(req.getParameter("price"));
-            int year = Integer.parseInt(req.getParameter("year"));
-            String categoryName = req.getParameter("category");
-            String description = req.getParameter("description");
-            String publisher = req.getParameter("publisher");
-            String image = req.getParameter("image");
+            try {
 
+                long isbn = Long.parseLong(req.getParameter("isbn"));
+                String title = req.getParameter("title");
+                String authorName = req.getParameter("author");
+                String priceString = req.getParameter("price");
+                String[] priceParts = priceString.split(",");
+                int price = Integer.parseInt(priceParts[0]) * 100;
+                if (priceParts.length >= 2) {
+                    if (priceParts[1].length() == 1) {
+                        price += Integer.parseInt(priceParts[1]) * 10;
+                    } else {
+                        price += Integer.parseInt(priceParts[1]);
+                    }
+                }
+                int year = Integer.parseInt(req.getParameter("year"));
+                String categoryName = req.getParameter("category");
+                String description = req.getParameter("description");
+                String publisher = req.getParameter("publisher");
+                String image = req.getParameter("image");
 
-            ArrayList<Author> authors = new ArrayList<>();
-            String[] authorNames = authorName.split(",");
-            for (String name : authorNames) {
-                authors.add(new Author(name));
+                //check isbn
+                List<Book> books = db.getBooks();
+                boolean found = false;
+                if (books != null) {
+                    for(Book b : books){
+                        if(b.getIsbn() == isbn){
+                            found = true;
+                            break;
+                        }
+                    }
+                }
+
+                if (found) {
+                    out.println("<aside class =\"m-note m-danger\">");
+                    out.println("<h3>Es gibt breits ein buch mit dieser ISBN </h3>");
+                    out.println("</aside>");
+                } else {
+                    ArrayList<Author> authors = new ArrayList<>();
+                    String[] authorNames = authorName.split(",");
+                    for (String name : authorNames) {
+                        authors.add(new Author(name));
+                    }
+                    Category category = new Category();
+                    category.setName(categoryName);
+                    Book book = new Book(isbn,
+                            authors,
+                            new Publisher(publisher),
+                            category,
+                            title, Year.of(year), price, description, image
+                    );
+                    db.insert(book);
+                    resp.sendRedirect("booklist");
+                }
+            }
+            catch (Exception e){
+                e.printStackTrace();
+                out.println("<aside class =\"m-note m-danger\">");
+                out.println("<h3>Es gibt ein Fehler in der Eingabe </h3>");
+                out.println("</aside>");
             }
-            Category category = new Category();
-            category.setName(categoryName);
-            Book book = new Book(isbn,
-                    authors,
-                    new Publisher(publisher),
-                    category,
-                    title, Year.of(year), price, description, image
-            );
-            db.insert(book);
 
-            resp.sendRedirect("booklist");
         }
 
-        resp.setCharacterEncoding("utf-8");
-        PrintWriter out = resp.getWriter();
-
-        //header template
-        Utillity.insertFile(out, "template_head.html");
 
 
+        //list all books
         List<Book> books = db.getBooks();
-
         if (books != null) {
 
             //book entries
@@ -92,18 +130,16 @@ public class BookList extends HttpServlet {
                 out.println("  </div>");
 
                 out.println("  <div class=\"m-col-l-4\">");
-                out.println("<h1>" + book.getTitle() + "</h1>");
-                out.println("   <br>");
+                out.println("<h2>" + book.getTitle() + "</h2>");
+                out.println("ISBN: " + book.getIsbn() + "</br>");
+
                 for (int i = 0; i < book.getAuthors().size(); i++) {
-                    out.println("   <h2>" + book.getAuthors().get(0).getName() + "</h2>");
+                    out.println("von " + book.getAuthors().get(0).getName());
                 }
-                out.println("   <br>");
-                out.print("   <h3>" + book.getPrice() / 100 + ",");
-                if (book.getPrice() % 100 < 10) {
-                    out.print("0");
-                }
-                out.println(book.getPrice() % 100 + " &euro;</h3>");
-                out.println("   <br>");
+
+                out.println("</br>Veröffentlicht von " + book.getPublisher().getName() + "");
+                out.println("</br></br>" + book.getDescription() + "");
+
                 out.println("  </div>");
 
                 out.println("  <div class=\"m-col-l-4\">");
@@ -113,6 +149,16 @@ public class BookList extends HttpServlet {
                 out.println("Entfernen");
                 out.println("</a>");
 
+                out.println("   <br>");
+                out.println("   <br>");
+
+                out.print("   <h3>" + book.getPrice() / 100 + ",");
+                if (book.getPrice() % 100 < 10) {
+                    out.print("0");
+                }
+
+                out.println(book.getPrice() % 100 + " &euro;</h3>");
+
                 out.println(" </div>");
                 out.println("   </div>");
                 out.println("  </div>");
diff --git a/src/main/java/de/hsel/itech/servlet/Utillity.java b/src/main/java/de/hsel/itech/servlet/Utillity.java
index dddceac..9521525 100644
--- a/src/main/java/de/hsel/itech/servlet/Utillity.java
+++ b/src/main/java/de/hsel/itech/servlet/Utillity.java
@@ -30,6 +30,15 @@ public class Utillity {
         out.println("</div>");
     }
 
+    static public void addValidationInput(PrintWriter out, String label, String name, String type, String value, String pattern){
+        out.println(" <div class=\"m-row\">");
+        out.println("  <div class=\"m-col-l-2 m-push-l-5\">");
+        out.println(label);
+        out.println("<input type=\"" + type + "\" name=\"" + name + "\" value=\"" + value + "\"required pattern=\"" + pattern + "\">");
+        out.println("</div>");
+        out.println("</div>");
+    }
+
     static public void addButton(PrintWriter out, String label, String url){
         out.println(" <div class=\"m-row\">");
         out.println("  <div class=\"m-col-l-4 m-push-l-4\">");
@@ -42,23 +51,10 @@ public class Utillity {
         out.println("</div>");
     }
 
-    static public void addTypeButton(PrintWriter out, String label, String type){
-        /*
-        out.println(" <div class=\"m-row\">");
-        out.println("  <div class=\"m-col-l-4 m-push-l-4\">");
-        out.println("   <div class=\"m-button m-success\">");
-        out.println("<a href=\"" + "" + "\">");
-        out.println(label);
-        out.println("<input class=\"m-button m-success\" type=\"" + type + "\" value=\"" + label + "\">");
-        out.println("</a>");
-        out.println(" </div>");
-        out.println("</div>");
-        out.println("</div>");
-    */
-
+    static public void addSubmitButton(PrintWriter out, String label){
         out.println(" <div class=\"m-row\">");
         out.println("  <div class=\"m-col-l-4 m-push-l-5\">");
-        out.println("  <input type=\"" + type + "\" value=\"" + label + "\">");
+        out.println("  <input type=\"" + "submit" + "\" value=\"" + label + "\">");
         out.println(" </div>");
         out.println("</div>");
     }
diff --git a/src/main/resources/database.sql b/src/main/resources/database.sql
index ecde032..9da8296 100644
--- a/src/main/resources/database.sql
+++ b/src/main/resources/database.sql
@@ -1,6 +1,6 @@
 CREATE TABLE IF NOT EXISTS test(id bigint primary key auto_increment, hello varchar(25));
 INSERT IGNORE INTO test(hello) values ('Welt');
-CREATE TABLE IF NOT EXISTS book (id bigint primary key auto_increment, isbn bigint unique, title varchar(50), description varchar(500), price int, year year, publisher bigint, category bigint, image varchar(11) unique);
+CREATE TABLE IF NOT EXISTS book (id bigint primary key auto_increment, isbn bigint unique, title varchar(50), description varchar(500), price int, year year, publisher bigint, category bigint, image varchar(11));
 CREATE TABLE IF NOT EXISTS publisher(id bigint primary key auto_increment, name varchar(50) unique);
 CREATE TABLE IF NOT EXISTS author(id bigint primary key auto_increment, name varchar(50) unique);
 CREATE TABLE IF NOT EXISTS author_book(author bigint, book bigint, primary key(author, book), foreign key (author) REFERENCES author(id), foreign key (book) references book(id));