Minor tidy-up

.gitignore

@@ -16,3 +16,28 @@ bin/
 .project
 .classpath
 .settings/
+
+### JetBrains template
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+
+# User-specific stuff
+.idea/**
+# File-based project format
+*.iws
+*.iml
+
+# IntelliJ
+out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties

src/main/java/org/prefixcommons/CurieUtil.java

@@ -1,12 +1,11 @@
 package org.prefixcommons;
 
-import static com.google.common.base.Preconditions.checkNotNull;
-
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Collection;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 
 import org.prefixcommons.trie.Trie;
@@ -17,7 +16,7 @@
 
 
 public class CurieUtil {
-  final private Trie trie;
+  private final Trie trie;
   private final ImmutableBiMap<String, String> curieMap;
 
   public CurieUtil(Map<String, String> mapping) {
@@ -92,14 +91,22 @@ public Optional<String> getCurie(String iri) {
     }
   }
 
+  public Optional<String> getCuriePrefix(String iri) {
+    String prefix = trie.getMatchingPrefix(iri);
+    if (prefix.equals("")) {
+      return Optional.empty();
+    }
+    return Optional.of(curieMap.inverse().get(prefix));
+  }
+
   /***
    * Expands a CURIE to a full IRI, if mapped.
    * 
    * @param curie The curie to expand.
    * @return an {@link Optional} IRI
    */
   public Optional<String> getIri(String curie) {
-    String[] parts = checkNotNull(curie).split(":");
+    String[] parts = Objects.requireNonNull(curie).split(":");
     if (parts.length > 1) {
       String prefix = parts[0];
       if (curieMap.containsKey(prefix)) {

src/main/java/org/prefixcommons/trie/Trie.java

@@ -1,6 +1,6 @@
 package org.prefixcommons.trie;
 
-import java.util.HashMap;
+import java.util.Map;
 
 /**
  * Data structure specific for characters, to efficiently resolve IRI prefixes to CURIEs prefixes.
@@ -25,7 +25,7 @@ public void insert(String word) {
 
     // Traverse through all characters of given word
     for (int level = 0; level < length; level++) {
-      HashMap<Character, TrieNode> child = crawl.getChildren();
+      Map<Character, TrieNode> child = crawl.getChildren();
       char ch = word.charAt(level);
 
       // If there is already a child for current character of given word
@@ -48,41 +48,43 @@ public void insert(String word) {
    * @return the longest matching prefix
    */
   public String getMatchingPrefix(String input) {
-    String result = ""; // Initialize resultant string
-    int length = input.length(); // Find length of the input string
+    StringBuilder result = new StringBuilder();
+    int length = input.length();
 
     // Initialize reference to traverse through Trie
     TrieNode crawl = root;
 
     // Iterate through all characters of input string 'str' and traverse
     // down the Trie
-    int level, prevMatch = 0;
-    for (level = 0; level < length; level++) {
+    int prevMatch = 0;
+    for (int level = 0; level < length; level++) {
       // Find current character of str
       char ch = input.charAt(level);
 
       // HashMap of current Trie node to traverse down
-      HashMap<Character, TrieNode> child = crawl.getChildren();
+      Map<Character, TrieNode> child = crawl.getChildren();
 
       // See if there is a Trie edge for the current character
       if (child.containsKey(ch)) {
-        result += ch; // Update result
+        result.append(ch); // Update result
         crawl = child.get(ch); // Update crawl to move down in Trie
 
         // If this is end of a word, then update prevMatch
-        if (crawl.isLeaf())
+        if (crawl.isLeaf()) {
           prevMatch = level + 1;
-      } else
+        }
+      } else {
         break;
+      }
     }
 
     // If the last processed character did not match end of a word,
     // return the previously matching prefix
-    if (!crawl.isLeaf())
+    if (!crawl.isLeaf()) {
       return result.substring(0, prevMatch);
-
-    else
-      return result;
+    } else {
+      return result.toString();
+    }
   }
 
 }

src/main/java/org/prefixcommons/trie/TrieNode.java

@@ -1,14 +1,15 @@
 package org.prefixcommons.trie;
 
 import java.util.HashMap;
+import java.util.Map;
 
 /**
  * Represents a Node in a Trie.
  *
  */
 class TrieNode {
   private char value;
-  private HashMap<Character, TrieNode> children;
+  private Map<Character, TrieNode> children;
   private boolean isLeaf;
 
   public TrieNode(char ch) {
@@ -17,7 +18,7 @@ public TrieNode(char ch) {
     isLeaf = false;
   }
 
-  public HashMap<Character, TrieNode> getChildren() {
+  public Map<Character, TrieNode> getChildren() {
     return children;
   }
 

src/test/java/org/prefixcommons/CurieUtilTest.java

@@ -50,6 +50,11 @@ public void fullIri_whenInputHasNoPrefix() {
     assertThat(util.getIri(":foo").get(), is("http://x.org/foo"));
   }
 
+  @Test(expected = NullPointerException.class)
+  public void throwsNullPointerWithNullInput() {
+    util.getIri(null);
+  }
+
   @Test
   public void curie_whenShortMappingIsPresent() {
     assertThat(util.getCurie("http://x.org/foo"), is(Optional.of(":foo")));
@@ -106,4 +111,9 @@ public void fromJsonLdFile() throws IOException {
         is(Optional.of("http://purl.obolibrary.org/obo/XAO_foo")));
   }
 
+  @Test
+  public void getIriPrefix() {
+    assertThat(util.getCuriePrefix("http://x.org/a_12345"), is(Optional.of("A")));
+    assertThat(util.getCuriePrefix("http://x.org/C_C12345"), is(Optional.of("CC")));
+  }
 }