Named Placeholders in String Formatting (#12576)

* Named Placeholders in String Formatting

* assert notEqualTo

core-java-modules/core-java-string-operations-4/src/main/java/com/baeldung/namedformatting/NamedFormatter.java

@@ -0,0 +1,31 @@
+package com.baeldung.namedformatting;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class NamedFormatter {
+    private NamedFormatter() {}
+
+    public static String format(String template, Map<String, Object> parameters) {
+        StringBuilder newTemplate = new StringBuilder(template);
+        List<Object> valueList = new ArrayList<>();
+
+        Matcher matcher = Pattern.compile("[$][{](\\w+)}").matcher(template);
+
+        while (matcher.find()) {
+            String key = matcher.group(1);
+
+            String paramName = "${" + key + "}";
+            int index = newTemplate.indexOf(paramName);
+            if (index != -1) {
+                newTemplate.replace(index, index + paramName.length(), "%s");
+                valueList.add(parameters.get(key));
+            }
+        }
+
+        return String.format(newTemplate.toString(), valueList.toArray());
+    }
+}

core-java-modules/core-java-string-operations-4/src/test/java/com/baeldung/namedformatting/NamedFormatterUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.namedformatting;
+
+import org.apache.commons.text.StrSubstitutor;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class NamedFormatterUnitTest {
+    private static final String TEMPLATE = "Text: [${text}] Number: [${number}] Text again: [${text}]";
+
+    @Test
+    void givenTemplateWithNamedParam_whenCallingCommonsTextStrSubstitutor_shouldGetExpectedResult() {
+        Map<String, Object> params = new HashMap<>();
+        params.put("text", "It's awesome!");
+        params.put("number", 42);
+        String result = StrSubstitutor.replace(TEMPLATE, params, "${", "}");
+        assertThat(result).isEqualTo("Text: [It's awesome!] Number: [42] Text again: [It's awesome!]");
+    }
+
+    @Test
+    void givenTemplateWithNamedParam_whenCallingCommonsTextStrSubstitutorWithParameterNames_shouldNotWorkAsExpected() {
+        Map<String, Object> params = new HashMap<>();
+        params.put("text", "'${number}' is a placeholder.");
+        params.put("number", 42);
+        String result = StrSubstitutor.replace(TEMPLATE, params, "${", "}");
+
+        assertThat(result).isNotEqualTo("Text: ['${number}' is a placeholder.] Number: [42] Text again: ['${number}' is a placeholder.]");
+
+        assertThat(result).isEqualTo("Text: ['42' is a placeholder.] Number: [42] Text again: ['42' is a placeholder.]");
+    }
+
+    @Test
+    void givenTemplateWithNamedParam_whenCallingNamedFormatter_shouldGetExpectedResult() {
+        Map<String, Object> params = new HashMap<>();
+        params.put("text", "It's awesome!");
+        params.put("number", 42);
+        String result = NamedFormatter.format(TEMPLATE, params);
+        assertThat(result).isEqualTo("Text: [It's awesome!] Number: [42] Text again: [It's awesome!]");
+
+        params.put("text", "'${number}' is a placeholder.");
+        result = NamedFormatter.format(TEMPLATE, params);
+        assertThat(result).isEqualTo("Text: ['${number}' is a placeholder.] Number: [42] Text again: ['${number}' is a placeholder.]");
+    }
+}