map methods

src/java.base/share/classes/java/lang/StringTemplate.java

@@ -387,6 +387,60 @@ static StringTemplate combine(List<StringTemplate> stringTemplates) {
         return JTA.combine(stringTemplates.toArray(new StringTemplate[0]));
     }
 
+    /**
+     * Constructs a new {@link StringTemplate} using this instance's values and
+     * fragments mapped from this instance's fragments by the specified
+     * {@code mapper} function. For example:
+     * {@snippet lang = JAVA:
+     * StringTemplate st2 = st1.mapFragments(f -> f.toUpperCase());
+     * }
+     * or
+     * {@snippet lan g =JAVA:
+     * StringTemplate st4 = st3.mapFragments(f -> {
+     *     if (f.contains("\"")) {
+     *         throw new RuntimeException("Should not use quotes in the template");
+     *     }
+     *     return f;
+     * });
+     * }
+     *
+     * @param mapper mapper function
+     * @return new {@link StringTemplate}
+     */
+    default StringTemplate mapFragments(Function<String, String> mapper) {
+        Objects.requireNonNull(mapper, "mapper must not be null");
+        List<String> fragments = fragments()
+            .stream()
+            .map(mapper)
+            .toList();
+        return StringTemplate.of(fragments, values());
+    }
+
+    /**
+     * Constructs a new {@link StringTemplate} using this instance's fragments and
+     * values mapped from this instance's values by the specified
+     * {@code mapper} function.
+     * {@snippet lan g =JAVA :
+     * StringTemplate st2 = st1.mapValue(v -> {
+     *      if (v instanceof Supplier<?> s) {
+     *          return s.get();
+     *      }
+     *      return v;
+     * });
+     * }
+     *
+     * @param mapper mapper function
+     * @return new {@link StringTemplate}
+     */
+    default StringTemplate mapValues(Function<Object, Object> mapper) {
+        Objects.requireNonNull(mapper, "mapper must not be null");
+        List<Object> values = values()
+            .stream()
+            .map(mapper)
+            .toList();
+        return StringTemplate.of(fragments(), values);
+    }
+
     /**
      * Test two {@link StringTemplate StringTemplates} for equality.
      *

test/jdk/java/lang/template/Basic.java

@@ -41,6 +41,7 @@ public static void main(String... arg) {
         limitsTests();
         stringTemplateCoverage();
         emptyExpressionTest();
+        mapTests();
     }
 
     static void ASSERT(String a, String b) {
@@ -398,4 +399,36 @@ static void emptyExpressionTest() {
         ASSERT("\{}".fragments().size(), 1);
         ASSERT("\{}".fragments().get(0), "");
     }
+
+    /*
+     *  mapFragments and mapValues
+     */
+    static void mapTests() {
+        int x = 10, y = 20;
+        StringTemplate st = "The sum of \{x} and \{y} equals \{x + y}";
+        StringTemplate st1 = st.mapFragments(String::toUpperCase);
+        StringTemplate st2 = st.mapValues(v -> v instanceof Integer i ? i * 100 : v);
+        ASSERT(st1.join(), "THE SUM OF 10 AND 20 EQUALS 30");
+        ASSERT(st2.join(), "The sum of 1000 and 2000 equals 3000");
+    }
+
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 }