diff --git a/src/main/java/de/hsel/itech/config/Configuration.java b/src/main/java/de/hsel/itech/config/Configuration.java
index 3412c35..c9aee3f 100644
--- a/src/main/java/de/hsel/itech/config/Configuration.java
+++ b/src/main/java/de/hsel/itech/config/Configuration.java
@@ -25,6 +25,8 @@ public class Configuration {
 
     @Getter
     private Database database;
+    @Getter
+    private Unsplash unsplash;
 
 
     /**
diff --git a/src/main/java/de/hsel/itech/config/Unsplash.java b/src/main/java/de/hsel/itech/config/Unsplash.java
new file mode 100644
index 0000000..3d77a1a
--- /dev/null
+++ b/src/main/java/de/hsel/itech/config/Unsplash.java
@@ -0,0 +1,20 @@
+package de.hsel.itech.config;
+
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import lombok.ToString;
+
+/**
+ * @author Johannes Theiner
+ * @version 0.1
+ * @since 0.1
+ **/
+
+@Getter
+@ToString
+@EqualsAndHashCode
+public class Unsplash {
+
+    private String accessKey;
+    private String secretKey;
+}
\ No newline at end of file
diff --git a/src/main/java/de/hsel/itech/db/Database.java b/src/main/java/de/hsel/itech/db/Database.java
index 8617ce0..1cf745f 100644
--- a/src/main/java/de/hsel/itech/db/Database.java
+++ b/src/main/java/de/hsel/itech/db/Database.java
@@ -126,7 +126,7 @@ public class Database {
      * @return {@link de.hsel.itech.db.pojo.Author}
      */
     @Nullable
-    public Author getAuthor(String name) {
+    public Author getAuthor(@NotNull String name) {
         Map.Entry<ResultSet, Connection> entry = getResultSetsByValue(author, "name", name);
         assert entry != null;
         assert entry.getKey() != null;
@@ -171,7 +171,7 @@ public class Database {
      * @return {@link de.hsel.itech.db.pojo.Category}
      */
     @Nullable
-    public Category getCategory(String name) {
+    public Category getCategory(@NotNull String name) {
         Map.Entry<ResultSet, Connection> entry = getResultSetsByValue(category, "name", name);
         assert entry != null;
 
@@ -243,7 +243,7 @@ public class Database {
      * @return {@link de.hsel.itech.db.pojo.Publisher}
      */
     @Nullable
-    public Publisher getPublisher(String name) {
+    public Publisher getPublisher(@NotNull String name) {
         Map.Entry<ResultSet, Connection> entry = getResultSetsByValue(publisher, "name", name);
         assert entry != null;
         assert entry.getKey() != null;
@@ -463,6 +463,7 @@ public class Database {
         assert publisher != null;
         assert category != null;
 
+        //insert book
         try {
             PreparedStatement statement = connection.prepareStatement("INSERT INTO book(isbn, title, description, " +
                     "price, year, publisher, category, image) VALUES (?, ?, ?, ?, ?, ?, ?, ?)", Statement.RETURN_GENERATED_KEYS);
@@ -481,6 +482,7 @@ public class Database {
                 lastId = resultSet.getLong("id");
             }
 
+            //add book to author
             for (Author author : authors) {
                 PreparedStatement authorStatement = connection.prepareStatement("INSERT INTO " + authorBook + " (author, book) VALUES (?, ?);");
                 authorStatement.setLong(1, author.getId());
@@ -633,7 +635,7 @@ public class Database {
      * @param table table name
      * @return deletion count
      */
-    private int delete(long id, String table) {
+    private int delete(long id, @NotNull String table) {
         Connection connection = getConnection();
         assert connection != null;
 
@@ -656,7 +658,7 @@ public class Database {
      * @param table table
      * @return list of ids
      */
-    private List<Long> getIds(String table) {
+    private List<Long> getIds(@NotNull String table) {
         Map.Entry<ResultSet, Connection> entry = getColumnsFromResultSet(table, "id");
         assert entry != null;
 
@@ -683,12 +685,12 @@ public class Database {
      * @return {@link java.util.Map.Entry}
      */
     @Nullable
-    private Map.Entry<ResultSet, Connection> getResultSetById(String table, long id) {
+    private Map.Entry<ResultSet, Connection> getResultSetById(@NotNull String table, long id) {
         return getResultSetByValue(table, "id", id);
     }
 
     @Nullable
-    private Map.Entry<ResultSet, Connection> getResultSetByValue(String table, String column, long value) {
+    private Map.Entry<ResultSet, Connection> getResultSetByValue(@NotNull String table, @NotNull String column, long value) {
         Connection connection = getConnection();
         try {
             assert connection != null;
@@ -793,7 +795,7 @@ public class Database {
     @Nullable
     private String getRandomImage() {
         try {
-            InputStream is = new URL("https://api.unsplash.com/photos/random?client_id=bb18673959b1cfd053a4ecb58e85bb8d99a0050ae5b71dac3e7632916eead9aa").openStream();
+            InputStream is = new URL("https://api.unsplash.com/photos/random?client_id=" + Configuration.get().getUnsplash().getAccessKey()).openStream();
             try {
                 BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
                 StringBuilder sb = new StringBuilder();
diff --git a/src/main/java/de/hsel/itech/servlet/AddBook.java b/src/main/java/de/hsel/itech/servlet/AddBook.java
index 321e023..77798b5 100644
--- a/src/main/java/de/hsel/itech/servlet/AddBook.java
+++ b/src/main/java/de/hsel/itech/servlet/AddBook.java
@@ -1,5 +1,7 @@
 package de.hsel.itech.servlet;
 
+import org.jetbrains.annotations.NotNull;
+
 import javax.servlet.annotation.WebServlet;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
@@ -10,7 +12,6 @@ import java.io.PrintWriter;
 /**
  * Servlet: form to add a book to the database
  *
- *
  * @author Julian Hinxlage
  * @version 0.1
  * @since 0.1
@@ -20,7 +21,7 @@ import java.io.PrintWriter;
 public class AddBook extends HttpServlet {
 
 
-    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
+    protected void doGet(@NotNull final HttpServletRequest req, @NotNull final HttpServletResponse resp)
             throws IOException {
 
         resp.setCharacterEncoding("utf-8");
@@ -30,19 +31,19 @@ public class AddBook extends HttpServlet {
 
         out.println("<form class=\"m-container\" action=\"booklist\" method=post>");
         Utillity.addValidationInput(out, "ISBN", "isbn", "text", "0", "[0-9]*");
-        Utillity.addInput(out,"Titel", "title");
-        Utillity.addInput(out,"Author", "author");
-        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");
+        Utillity.addInput(out, "Titel", "title");
+        Utillity.addInput(out, "Author", "author");
+        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");
         Utillity.addSubmitButton(out, "Hinzufügen");
         out.println("</form>");
 
 
-        Utillity.addButton(out,"Zurück zur Buchliste", "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 99ac43c..b2f2ddc 100644
--- a/src/main/java/de/hsel/itech/servlet/BookList.java
+++ b/src/main/java/de/hsel/itech/servlet/BookList.java
@@ -5,6 +5,7 @@ import de.hsel.itech.db.pojo.Author;
 import de.hsel.itech.db.pojo.Book;
 import de.hsel.itech.db.pojo.Category;
 import de.hsel.itech.db.pojo.Publisher;
+import org.jetbrains.annotations.NotNull;
 
 import javax.servlet.annotation.WebServlet;
 import javax.servlet.http.HttpServlet;
@@ -20,7 +21,6 @@ import java.util.List;
 /**
  * Servlet: list of all books and remove function
  *
- *
  * @author Julian Hinxlage
  * @version 0.1
  * @since 0.1
@@ -29,14 +29,19 @@ import java.util.List;
 @WebServlet("/booklist")
 public class BookList extends HttpServlet {
 
-    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
-            throws IOException {
+    @Override
+    protected void doGet(@NotNull HttpServletRequest req, @NotNull HttpServletResponse resp) throws IOException {
+       doPost(req, resp);
+    }
+
+    @Override
+    protected void doPost(@NotNull final HttpServletRequest req, @NotNull final HttpServletResponse resp) throws IOException {
         req.setCharacterEncoding(StandardCharsets.UTF_8.name());
 
         //get database object
         Database db = Database.getInstance();
 
-        resp.setCharacterEncoding("utf-8");
+        resp.setCharacterEncoding(StandardCharsets.UTF_8.name());
         PrintWriter out = resp.getWriter();
 
         //header template
@@ -94,8 +99,7 @@ public class BookList extends HttpServlet {
                     db.insert(book);
                     resp.sendRedirect("booklist");
                 }
-            }
-            catch (Exception e){
+            } catch (Exception e) {
                 e.printStackTrace();
                 out.println("<aside class =\"m-note m-danger\">");
                 out.println("<h3>Es gibt ein Fehler in der Eingabe </h3>");
@@ -105,7 +109,6 @@ public class BookList extends HttpServlet {
         }
 
 
-
         //list all books
         List<Book> books = db.getBooks();
         if (books != null) {
@@ -125,7 +128,7 @@ public class BookList extends HttpServlet {
                 out.println("ISBN: " + book.getIsbn() + "</br>");
 
                 List<String> authors = new ArrayList<>();
-                for(Author author : book.getAuthors()) {
+                for (Author author : book.getAuthors()) {
                     authors.add(author.getName());
                 }
 
@@ -167,9 +170,4 @@ public class BookList extends HttpServlet {
         Utillity.insertFile(out, "template_footer.html");
     }
 
-    protected void doPost(final HttpServletRequest req, final HttpServletResponse resp)
-            throws IOException {
-        doGet(req, resp);
-    }
-
 }
diff --git a/src/main/java/de/hsel/itech/servlet/Utillity.java b/src/main/java/de/hsel/itech/servlet/Utillity.java
index 9521525..34c432e 100644
--- a/src/main/java/de/hsel/itech/servlet/Utillity.java
+++ b/src/main/java/de/hsel/itech/servlet/Utillity.java
@@ -1,14 +1,22 @@
 package de.hsel.itech.servlet;
 
+import org.jetbrains.annotations.NotNull;
+
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.util.Objects;
 
+/**
+ * @author Julian Hinxlage
+ * @version 0.1
+ * @since 0.1
+ */
 public class Utillity {
 
-    static public void insertFile(PrintWriter out, String fileName) {
-        try (BufferedReader br = new BufferedReader(new FileReader(Utillity.class.getClassLoader().getResource(fileName).getFile()))) {
+    public static void insertFile(@NotNull PrintWriter out, @NotNull String fileName) {
+        try (BufferedReader br = new BufferedReader(new FileReader(Objects.requireNonNull(Utillity.class.getClassLoader().getResource(fileName)).getFile()))) {
             for (String line = br.readLine(); line != null; line = br.readLine()) {
                 out.println(line);
             }
@@ -17,11 +25,11 @@ public class Utillity {
         }
     }
 
-    static public void addInput(PrintWriter out, String label, String name){
-        addInput(out,label,name,"");
+    public static void addInput(@NotNull PrintWriter out, @NotNull String label, @NotNull String name) {
+        addInput(out, label, name, "");
     }
 
-    static public void addInput(PrintWriter out, String label, String name, String value){
+    public static void addInput(@NotNull PrintWriter out, @NotNull String label, @NotNull String name, @NotNull String value) {
         out.println(" <div class=\"m-row\">");
         out.println("  <div class=\"m-col-l-2 m-push-l-5\">");
         out.println(label);
@@ -30,7 +38,7 @@ public class Utillity {
         out.println("</div>");
     }
 
-    static public void addValidationInput(PrintWriter out, String label, String name, String type, String value, String pattern){
+    public static void addValidationInput(@NotNull PrintWriter out, @NotNull String label, @NotNull String name, @NotNull String type, @NotNull String value, @NotNull String pattern) {
         out.println(" <div class=\"m-row\">");
         out.println("  <div class=\"m-col-l-2 m-push-l-5\">");
         out.println(label);
@@ -39,7 +47,7 @@ public class Utillity {
         out.println("</div>");
     }
 
-    static public void addButton(PrintWriter out, String label, String url){
+    public static void addButton(@NotNull PrintWriter out, @NotNull String label, @NotNull String url) {
         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\">");
@@ -51,7 +59,7 @@ public class Utillity {
         out.println("</div>");
     }
 
-    static public void addSubmitButton(PrintWriter out, String label){
+    public static void addSubmitButton(@NotNull PrintWriter out, @NotNull String label) {
         out.println(" <div class=\"m-row\">");
         out.println("  <div class=\"m-col-l-4 m-push-l-5\">");
         out.println("  <input type=\"" + "submit" + "\" value=\"" + label + "\">");