Use StringJoiner where possible to simplify String joining

Closes gh-23300

spring-core/src/main/java/org/springframework/core/style/DefaultValueStyler.java

@@ -18,10 +18,10 @@ package org.springframework.core.style;
 
 import java.lang.reflect.Method;
 import java.util.Collection;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.StringJoiner;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
@@ -82,20 +82,15 @@ public class DefaultValueStyler implements ValueStyler {
 	}
 
 	private <K, V> String style(Map<K, V> value) {
-		StringBuilder result = new StringBuilder(value.size() * 8 + 16);
-		result.append(MAP + "[");
-		for (Iterator<Map.Entry<K, V>> it = value.entrySet().iterator(); it.hasNext();) {
-			Map.Entry<K, V> entry = it.next();
-			result.append(style(entry));
-			if (it.hasNext()) {
-				result.append(',').append(' ');
-			}
-		}
 		if (value.isEmpty()) {
-			result.append(EMPTY);
+			return MAP + '[' + EMPTY + ']';
+		}
+
+		StringJoiner result = new StringJoiner(", ", "[", "]");
+		for (Map.Entry<K, V> entry : value.entrySet()) {
+			result.add(style(entry));
 		}
-		result.append("]");
-		return result.toString();
+		return MAP + result;
 	}
 
 	private String style(Map.Entry<?, ?> value) {
@@ -103,19 +98,17 @@ public class DefaultValueStyler implements ValueStyler {
 	}
 
 	private String style(Collection<?> value) {
-		StringBuilder result = new StringBuilder(value.size() * 8 + 16);
-		result.append(getCollectionTypeString(value)).append('[');
-		for (Iterator<?> i = value.iterator(); i.hasNext();) {
-			result.append(style(i.next()));
-			if (i.hasNext()) {
-				result.append(',').append(' ');
-			}
-		}
+		String collectionType = getCollectionTypeString(value);
+
 		if (value.isEmpty()) {
-			result.append(EMPTY);
+			return collectionType + '[' + EMPTY + ']';
 		}
-		result.append("]");
-		return result.toString();
+
+		StringJoiner result = new StringJoiner(", ", "[", "]");
+		for (Object o : value) {
+			result.add(style(o));
+		}
+		return collectionType + result;
 	}
 
 	private String getCollectionTypeString(Collection<?> value) {
@@ -131,20 +124,15 @@ public class DefaultValueStyler implements ValueStyler {
 	}
 
 	private String styleArray(Object[] array) {
-		StringBuilder result = new StringBuilder(array.length * 8 + 16);
-		result.append(ARRAY + "<").append(ClassUtils.getShortName(array.getClass().getComponentType())).append(">[");
-		for (int i = 0; i < array.length - 1; i++) {
-			result.append(style(array[i]));
-			result.append(',').append(' ');
-		}
-		if (array.length > 0) {
-			result.append(style(array[array.length - 1]));
+		if (array.length == 0) {
+			return ARRAY + '<' + ClassUtils.getShortName(array.getClass().getComponentType()) + '>' + '[' + EMPTY + ']';
 		}
-		else {
-			result.append(EMPTY);
+
+		StringJoiner result = new StringJoiner(", ", "[", "]");
+		for (Object o : array) {
+			result.add(style(o));
 		}
-		result.append("]");
-		return result.toString();
+		return ARRAY + '<' + ClassUtils.getShortName(array.getClass().getComponentType()) + '>' + result;
 	}
 
 }

spring-core/src/main/java/org/springframework/util/ObjectUtils.java

@@ -734,19 +734,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (boolean b : array) {
+			sj.add(String.valueOf(b));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -766,18 +758,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (byte b : array) {
+			sj.add(String.valueOf(b));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -797,18 +782,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-			sb.append("'").append(array[i]).append("'");
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (char c : array) {
+			sj.add('\'' + String.valueOf(c) + '\'');
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -828,19 +806,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (double d : array) {
+			sj.add(String.valueOf(d));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -860,19 +830,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (float f : array) {
+			sj.add(String.valueOf(f));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -892,18 +854,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (int i : array) {
+			sj.add(String.valueOf(i));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -923,18 +878,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (long l : array) {
+			sj.add(String.valueOf(l));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**
@@ -954,18 +902,11 @@ public abstract class ObjectUtils {
 		if (length == 0) {
 			return EMPTY_ARRAY;
 		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < length; i++) {
-			if (i == 0) {
-				sb.append(ARRAY_START);
-			}
-			else {
-				sb.append(ARRAY_ELEMENT_SEPARATOR);
-			}
-			sb.append(array[i]);
+		StringJoiner sj = new StringJoiner(ARRAY_ELEMENT_SEPARATOR, ARRAY_START, ARRAY_END);
+		for (short s : array) {
+			sj.add(String.valueOf(s));
 		}
-		sb.append(ARRAY_END);
-		return sb.toString();
+		return sj.toString();
 	}
 
 }

spring-core/src/test/java/org/springframework/core/style/DefaultValueStylerTest.java

+package org.springframework.core.style;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DefaultValueStylerTest {
+
+	private DefaultValueStyler styler = new DefaultValueStyler();
+
+	@Test
+	public void style() throws NoSuchMethodException {
+		assertThat(styler.style(null)).isEqualTo("[null]");
+
+		assertThat(styler.style("str")).isEqualTo("'str'");
+
+		assertThat(styler.style(String.class)).isEqualTo("String");
+
+		assertThat(styler.style(String.class.getMethod("toString"))).isEqualTo("toString@String");
+	}
+
+	@Test
+	public void style_plainObject() {
+		final Object obj = new Object();
+
+		assertThat(styler.style(obj)).isEqualTo(String.valueOf(obj));
+	}
+
+	@Test
+	public void style_map() {
+		Map<String, Integer> map = Collections.emptyMap();
+		assertThat(styler.style(map)).isEqualTo("map[[empty]]");
+
+		map = Collections.singletonMap("key", 1);
+		assertThat(styler.style(map)).isEqualTo("map['key' -> 1]");
+
+		map = new HashMap<>();
+		map.put("key1", 1);
+		map.put("key2", 2);
+		assertThat(styler.style(map)).isEqualTo("map['key1' -> 1, 'key2' -> 2]");
+	}
+
+	@Test
+	public void style_entry() {
+		final Map<String, Integer> map = new LinkedHashMap<>();
+		map.put("key1", 1);
+		map.put("key2", 2);
+
+		final Iterator<Map.Entry<String, Integer>> entries = map.entrySet().iterator();
+
+		assertThat(styler.style(entries.next())).isEqualTo("'key1' -> 1");
+		assertThat(styler.style(entries.next())).isEqualTo("'key2' -> 2");
+	}
+
+	@Test
+	public void style_collection() {
+		List<Integer> list = Collections.emptyList();
+		assertThat(styler.style(list)).isEqualTo("list[[empty]]");
+
+		list = Collections.singletonList(1);
+		assertThat(styler.style(list)).isEqualTo("list[1]");
+
+		list = Arrays.asList(1, 2);
+		assertThat(styler.style(list)).isEqualTo("list[1, 2]");
+	}
+
+	@Test
+	public void style_primitiveArray() {
+		int[] array = new int[0];
+		assertThat(styler.style(array)).isEqualTo("array<Object>[[empty]]");
+
+		array = new int[]{1};
+		assertThat(styler.style(array)).isEqualTo("array<Integer>[1]");
+
+		array = new int[]{1, 2};
+		assertThat(styler.style(array)).isEqualTo("array<Integer>[1, 2]");
+	}
+
+	@Test
+	public void style_objectArray() {
+		String[] array = new String[0];
+		assertThat(styler.style(array)).isEqualTo("array<String>[[empty]]");
+
+		array = new String[]{"str1"};
+		assertThat(styler.style(array)).isEqualTo("array<String>['str1']");
+
+		array = new String[]{"str1", "str2"};
+		assertThat(styler.style(array)).isEqualTo("array<String>['str1', 'str2']");
+	}
+
+}
\ No newline at end of file