Added toString() implementation to model classes (#271)

src/main/java/org/gitlab4j/api/models/TreeItem.java

@@ -4,6 +4,8 @@ import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.XmlRootElement;
 
+import org.gitlab4j.api.utils.JacksonJson;
+
 @XmlRootElement
 @XmlAccessorType(XmlAccessType.FIELD)
 public class TreeItem {
@@ -61,4 +63,9 @@ public class TreeItem {
     public void setType(Type type) {
         this.type = type;
     }
+
+    @Override
+    public String toString() {
+        return (JacksonJson.toJsonString(this));
+    }
 }

src/main/java/org/gitlab4j/api/models/User.java

@@ -2,6 +2,8 @@ package org.gitlab4j.api.models;
 
 import javax.xml.bind.annotation.XmlRootElement;
 
+import org.gitlab4j.api.utils.JacksonJson;
+
 @XmlRootElement
 public class User extends AbstractUser<User> {
 
@@ -46,4 +48,8 @@ public class User extends AbstractUser<User> {
         return withSharedRunnersMinutesLimit(sharedRunnersMinuteLimit);
     }
 
+    @Override
+    public String toString() {
+        return (JacksonJson.toJsonString(this));
+    }
 }

src/main/java/org/gitlab4j/api/models/WikiPage.java

@@ -27,6 +27,8 @@ import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.XmlRootElement;
 
+import org.gitlab4j.api.utils.JacksonJson;
+
 @XmlRootElement
 @XmlAccessorType(XmlAccessType.FIELD)
 public class WikiPage {
@@ -76,4 +78,9 @@ public class WikiPage {
     public void setFormat(String format) {
         this.format = format;
     }
+
+    @Override
+    public String toString() {
+        return (JacksonJson.toJsonString(this));
+    }
 }