introduce custom exception class instead of RuntimeExceptions (#10)

We now use a custom, checked exceptions on errors that can occur
with the API communication or configuration. instead of throwing an
unchecked IllegalStateException.

src/main/java/de/stklcode/pubtrans/ura/exception/UraClientConfigurationException.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2016-2020 Stefan Kalscheuer
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package de.stklcode.pubtrans.ura.exception;
+
+/**
+ * Custom exception class indicating an error with the URA client configuration.
+ *
+ * @author Stefan Kalscheuer
+ * @since 2.0
+ */
+public class UraClientConfigurationException extends UraClientException {
+    private static final long serialVersionUID = -8035752391477338659L;
+
+    /**
+     * Default constructor.
+     *
+     * @param message The detail message (which is saved for later retrieval by the {@link #getMessage()} method)
+     * @param cause   The cause (which is saved for later retrieval by the {@link #getCause()} method).
+     */
+    public UraClientConfigurationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

src/main/java/de/stklcode/pubtrans/ura/exception/UraClientException.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2016-2020 Stefan Kalscheuer
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package de.stklcode.pubtrans.ura.exception;
+
+import java.io.IOException;
+
+/**
+ * Custom exception class indicating an error with the URA API communication.
+ *
+ * @author Stefan Kalscheuer
+ * @since 2.0
+ */
+public class UraClientException extends IOException {
+    private static final long serialVersionUID = 4585240685746203433L;
+
+    /**
+     * Default constructor.
+     *
+     * @param message The detail message (which is saved for later retrieval by the {@link #getMessage()} method)
+     * @param cause   The cause (which is saved for later retrieval by the {@link #getCause()} method).
+     */
+    public UraClientException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}