Add support for custom violation exceptions

scm-core/src/main/java/sonia/scm/ScmConstraintViolationException.java

@@ -0,0 +1,76 @@
+package sonia.scm;
+
+import java.util.ArrayList;
+import java.util.Collection;
+
+import static java.util.Collections.unmodifiableCollection;
+
+public class ScmConstraintViolationException extends RuntimeException {
+
+  private final Collection<ScmConstraintViolation> violations;
+
+  private final String furtherInformations;
+
+  private ScmConstraintViolationException(Collection<ScmConstraintViolation> violations, String furtherInformations) {
+    this.violations = violations;
+    this.furtherInformations = furtherInformations;
+  }
+
+  public Collection<ScmConstraintViolation> getViolations() {
+    return unmodifiableCollection(violations);
+  }
+
+  public String getUrl() {
+    return furtherInformations;
+  }
+
+  public static class Builder {
+    private final Collection<ScmConstraintViolation> violations = new ArrayList<>();
+    private String furtherInformations;
+
+    public static Builder doThrow() {
+      Builder builder = new Builder();
+      return builder;
+    }
+
+    public Builder andThrow() {
+      this.violations.clear();
+      this.furtherInformations = null;
+      return this;
+    }
+
+    public Builder violation(String message, String... pathElements) {
+      this.violations.add(new ScmConstraintViolation(message, pathElements));
+      return this;
+    }
+
+    public Builder withFurtherInformations(String furtherInformations) {
+      this.furtherInformations = furtherInformations;
+      return this;
+    }
+
+    public void when(boolean condition) {
+      if (condition && !this.violations.isEmpty()) {
+        throw new ScmConstraintViolationException(violations, furtherInformations);
+      }
+    }
+  }
+
+  public static class ScmConstraintViolation {
+    private final String message;
+    private final String path;
+
+    private ScmConstraintViolation(String message, String... pathElements) {
+      this.message = message;
+      this.path = String.join(".", pathElements);
+    }
+
+    public String getMessage() {
+      return message;
+    }
+
+    public String getPropertyPath() {
+      return path;
+    }
+  }
+}