diff --git a/pom.xml b/pom.xml
index b2c9ace..7f9bb0b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -146,6 +146,12 @@
             <version>1.1.1</version>
         </dependency>
 
+        <dependency>
+            <groupId>javax.validation</groupId>
+            <artifactId>validation-api</artifactId>
+            <version>2.0.1.Final</version>
+        </dependency>
+
 
         <!--Database-->
         <dependency>
diff --git a/src/main/java/de/hsel/itech/jsf/AddressBean.java b/src/main/java/de/hsel/itech/jsf/AddressBean.java
index c8e33f2..bfae7ff 100644
--- a/src/main/java/de/hsel/itech/jsf/AddressBean.java
+++ b/src/main/java/de/hsel/itech/jsf/AddressBean.java
@@ -9,6 +9,7 @@ import lombok.Setter;
 import javax.faces.bean.ManagedBean;
 import javax.faces.bean.SessionScoped;
 import javax.faces.context.FacesContext;
+import javax.validation.constraints.Size;
 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
@@ -41,6 +42,7 @@ public class AddressBean implements Serializable {
 
     @Getter
     @Setter
+    @Size(min = 5, max = 5)
     private Integer zipCode;
 
     @Getter
diff --git a/src/main/java/de/hsel/itech/jsf/UserBean.java b/src/main/java/de/hsel/itech/jsf/UserBean.java
index 09dac89..8390234 100644
--- a/src/main/java/de/hsel/itech/jsf/UserBean.java
+++ b/src/main/java/de/hsel/itech/jsf/UserBean.java
@@ -5,8 +5,12 @@ import de.hsel.itech.db.pojo.User;
 import lombok.Getter;
 import lombok.Setter;
 
+import javax.faces.application.FacesMessage;
 import javax.faces.bean.ManagedBean;
 import javax.faces.bean.SessionScoped;
+import javax.faces.context.FacesContext;
+import javax.validation.constraints.Pattern;
+import javax.validation.constraints.Size;
 import java.io.Serializable;
 
 @ManagedBean
@@ -19,10 +23,12 @@ public class UserBean implements Serializable {
 
     @Getter
     @Setter
+    @Size(min = 1)
     private String username;
 
     @Getter
     @Setter
+    @Pattern(regexp = "(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])")
     private String email;
 
     @Getter
@@ -65,6 +71,10 @@ public class UserBean implements Serializable {
         Database db = Database.getInstance();
 
         if(username != null && email != null && password != null) {
+            if(db.user().get(username) != null) {
+                FacesContext.getCurrentInstance().addMessage("register:username", new FacesMessage("Dieser Nutzername ist bereits vergeben"));
+                return "register.xhtml";
+            }
             User user = new User(email, username, password, (short) 1);
             db.user().insert(user);
             email = null;
diff --git a/src/main/webapp/register.xhtml b/src/main/webapp/register.xhtml
index 3dae1c5..62d75ab 100644
--- a/src/main/webapp/register.xhtml
+++ b/src/main/webapp/register.xhtml
@@ -11,8 +11,9 @@
 
             <div class="m-row">
                 <div class="m-col-l-6 m-push-l-4">
-                    <h:form>
+                    <h:form id="register">
                         <h:inputText id="username" value="#{userBean.username}">Nutzername</h:inputText>
+                        <h:message for="username"/>
                         <br/>
                         <h:inputText id="email" value="#{userBean.email}">Email</h:inputText>
                         <br/>