From e8168990c5419748c1a5c3012131a3f7ac091861 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogdan=20Cardo=C5=9F?=
 <106325528+sodrac@users.noreply.github.com>
Date: Fri, 30 Sep 2022 07:38:08 +0300
Subject: [PATCH] BAEL-5754 Convert a List of String to a comma-separated
 String (#12737)

* BAEL-5617 Handle classes with the same name in Java

code samples

* BAEL-5617 Handle classes with the same name in Java

update project module

* BAEL-5754 Convert a List of String to a comma-separated String

code samples

* BAEL-5754 update unit test class name

* BAEL-5754 update unit test methods naming

* BAEL-5754 update tests order so to reflect the article
---
 .../core-java-collections-list-4/pom.xml      |   7 +
 .../list/tostring/ListToStringUnitTest.java   | 132 ++++++++++++++++++
 2 files changed, 139 insertions(+)
 create mode 100644 core-java-modules/core-java-collections-list-4/src/test/java/com/baeldung/list/tostring/ListToStringUnitTest.java

diff --git a/core-java-modules/core-java-collections-list-4/pom.xml b/core-java-modules/core-java-collections-list-4/pom.xml
index 773f8c105b..49b3f849d4 100644
--- a/core-java-modules/core-java-collections-list-4/pom.xml
+++ b/core-java-modules/core-java-collections-list-4/pom.xml
@@ -56,6 +56,12 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+    	<dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-core</artifactId>
+            <version>${spring.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -80,6 +86,7 @@
         <assertj.version>3.22.0</assertj.version>
         <maven.compiler.source.version>17</maven.compiler.source.version>
         <maven.compiler.target.version>17</maven.compiler.target.version>
+        <spring.version>5.3.22</spring.version>
     </properties>
 
 </project>
\ No newline at end of file
diff --git a/core-java-modules/core-java-collections-list-4/src/test/java/com/baeldung/list/tostring/ListToStringUnitTest.java b/core-java-modules/core-java-collections-list-4/src/test/java/com/baeldung/list/tostring/ListToStringUnitTest.java
new file mode 100644
index 0000000000..479ccaf92f
--- /dev/null
+++ b/core-java-modules/core-java-collections-list-4/src/test/java/com/baeldung/list/tostring/ListToStringUnitTest.java
@@ -0,0 +1,132 @@
+package com.baeldung.list.tostring;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.StringJoiner;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+
+class ListToStringUnitTest {
+
+    @Test
+    void givenAListOfString_whenUsingJava8_thenConvertToStringByUsingString() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        String commaSeparatedString = String.join(",", arraysAsList);
+
+        assertThat(commaSeparatedString).isEqualTo("ONE,TWO,THREE");
+    }
+
+    @Test
+    void givenAListOfString_whenUsingJava8_thenConvertToStringByUsingStringJoiner() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        StringJoiner stringJoiner = new StringJoiner(",");
+        arraysAsList.stream()
+            .forEach(v -> stringJoiner.add(v));
+        String commaSeparatedString = stringJoiner.toString();
+
+        assertThat(commaSeparatedString).isEqualTo("ONE,TWO,THREE");
+
+        StringJoiner stringJoinerWithDelimiterPrefixSuffix = new StringJoiner(",", "[", "]");
+        arraysAsList.stream()
+            .forEach(v -> stringJoinerWithDelimiterPrefixSuffix.add(v));
+        String commaSeparatedStringWithDelimiterPrefixSuffix = stringJoinerWithDelimiterPrefixSuffix.toString();
+
+        assertThat(commaSeparatedStringWithDelimiterPrefixSuffix).isEqualTo("[ONE,TWO,THREE]");
+    }
+
+    @Test
+    void givenAListOfString_whenUsingJava8_thenConvertToStringByUsingCollectors() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        String commaSeparatedUsingCollect = arraysAsList.stream()
+            .collect(Collectors.joining(","));
+
+        assertThat(commaSeparatedUsingCollect).isEqualTo("ONE,TWO,THREE");
+
+        String commaSeparatedObjectToString = arraysAsList.stream()
+            .map(Object::toString)
+            .collect(Collectors.joining(","));
+
+        assertThat(commaSeparatedObjectToString).isEqualTo("ONE,TWO,THREE");
+
+        String commaSeparatedStringValueOf = arraysAsList.stream()
+            .map(String::valueOf)
+            .collect(Collectors.joining(","));
+
+        assertThat(commaSeparatedStringValueOf).isEqualTo("ONE,TWO,THREE");
+
+        String commaSeparatedStringValueOfWithDelimiterPrefixSuffix = arraysAsList.stream()
+            .map(String::valueOf)
+            .collect(Collectors.joining(",", "[", "]"));
+
+        assertThat(commaSeparatedStringValueOfWithDelimiterPrefixSuffix).isEqualTo("[ONE,TWO,THREE]");
+
+        String commaSeparatedUsingReduce = arraysAsList.stream()
+            .reduce((x, y) -> x + "," + y)
+            .get();
+
+        assertThat(commaSeparatedUsingReduce).isEqualTo("ONE,TWO,THREE");
+    }
+
+    @Test
+    void givenAListOfString_whenUsingApacheCommonsLang_thenConvertToStringByUsingStringUtils() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        String commaSeparatedString = org.apache.commons.lang3.StringUtils.join(arraysAsList, ",");
+
+        assertThat(commaSeparatedString).isEqualTo("ONE,TWO,THREE");
+
+        String commaSeparatedStringIndex = org.apache.commons.lang3.StringUtils.join(arraysAsList.toArray(), ",", 0, 3);
+
+        assertThat(commaSeparatedStringIndex).isEqualTo("ONE,TWO,THREE");
+    }
+
+    @Test
+    void givenAListOfString_whenUsingSpringCore_thenConvertToStringByUsingStringUtils() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        String collectionToCommaDelimitedString = org.springframework.util.StringUtils.collectionToCommaDelimitedString(arraysAsList);
+
+        assertThat(collectionToCommaDelimitedString).isEqualTo("ONE,TWO,THREE");
+
+        String collectionToDelimitedString = org.springframework.util.StringUtils.collectionToDelimitedString(arraysAsList, ",");
+
+        assertThat(collectionToDelimitedString).isEqualTo("ONE,TWO,THREE");
+    }
+
+    @Test
+    void givenAListOfString_whenUsingGoogleGuava_thenConvertToStringByUsingJoiner() {
+
+        List<String> arraysAsList = Arrays.asList("ONE", "TWO", "THREE");
+
+        String commaSeparatedString = com.google.common.base.Joiner.on(",")
+            .join(arraysAsList);
+
+        assertThat(commaSeparatedString).isEqualTo("ONE,TWO,THREE");
+
+        List<String> arraysAsListWithNull = Arrays.asList("ONE", null, "TWO", null, "THREE");
+
+        String commaSeparatedStringSkipNulls = com.google.common.base.Joiner.on(",")
+            .skipNulls()
+            .join(arraysAsListWithNull);
+
+        assertThat(commaSeparatedStringSkipNulls).isEqualTo("ONE,TWO,THREE");
+
+        String commaSeparatedStringUseForNull = com.google.common.base.Joiner.on(",")
+            .useForNull(" ")
+            .join(arraysAsListWithNull);
+
+        assertThat(commaSeparatedStringUseForNull).isEqualTo("ONE, ,TWO, ,THREE");
+    }
+
+}