MINOR: Use `Files.readString/writeString` and `String.repeat` to simplify code (#18372)

The 3 methods were introduced in Java 11.

Reviewers: Divij Vaidya <diviv@amazon.com>

clients/src/main/java/org/apache/kafka/common/config/provider/DirectoryConfigProvider.java

@@ -24,7 +24,6 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Map;
@@ -117,7 +116,7 @@ public class DirectoryConfigProvider implements ConfigProvider {
 
     private static String read(Path path) {
         try {
-            return new String(Files.readAllBytes(path), StandardCharsets.UTF_8);
+            return Files.readString(path);
         } catch (IOException e) {
             log.error("Could not read file {} for property {}", path, path.getFileName(), e);
             throw new ConfigException("Could not read file " + path + " for property " + path.getFileName());

clients/src/test/java/org/apache/kafka/clients/consumer/internals/AbstractStickyAssignorTest.java

@@ -1426,14 +1426,8 @@ public abstract class AbstractStickyAssignorTest {
     }
 
     private String pad(int num, int digits) {
-        StringBuilder sb = new StringBuilder();
         int iDigits = Integer.toString(num).length();
-
-        for (int i = 1; i <= digits - iDigits; ++i)
-            sb.append("0");
-
-        sb.append(num);
-        return sb.toString();
+        return "0".repeat(Math.max(0, digits - iDigits)) + num;
     }
 
     protected static List<String> topics(String... topics) {

core/src/test/java/kafka/security/minikdc/MiniKdc.java

@@ -443,7 +443,7 @@ public class MiniKdc {
             reader.lines().forEach(line -> stringBuilder.append(line).append("{3}"));
         }
         String output = MessageFormat.format(stringBuilder.toString(), realm, host, String.valueOf(port), System.lineSeparator());
-        Files.write(krb5conf.toPath(), output.getBytes(StandardCharsets.UTF_8));
+        Files.writeString(krb5conf.toPath(), output);
     }
 
     private void refreshJvmKerberosConfig() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {

generator/src/main/java/org/apache/kafka/message/CodeBuffer.java

@@ -58,11 +58,7 @@ public class CodeBuffer {
     }
 
     private String indentSpaces() {
-        StringBuilder bld = new StringBuilder();
-        for (int i = 0; i < indent; i++) {
-            bld.append("    ");
-        }
-        return bld.toString();
+        return "    ".repeat(Math.max(0, indent));
     }
 
     @Override

server/src/test/java/org/apache/kafka/server/metrics/LinuxIoMetricsCollectorTest.java

@@ -25,7 +25,6 @@ import org.junit.jupiter.api.Timeout;
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 
@@ -87,7 +86,7 @@ public class LinuxIoMetricsCollectorTest {
                          "read_bytes: " + readBytes + "\n" +
                          "write_bytes: " + writeBytes + "\n" +
                          "cancelled_write_bytes: 0\n";
-            Files.write(selfDir.resolve("io"), bld.getBytes(StandardCharsets.UTF_8));
+            Files.writeString(selfDir.resolve("io"), bld);
         }
     }
 }

shell/src/main/java/org/apache/kafka/shell/node/printer/ShellNodePrinter.java

@@ -35,13 +35,7 @@ public class ShellNodePrinter implements MetadataNodePrinter {
     }
 
     String indentationString() {
-        StringBuilder bld = new StringBuilder();
-        for (int i = 0; i < indentationLevel; i++) {
-            for (int j = 0; j < 2; j++) {
-                bld.append(" ");
-            }
-        }
-        return bld.toString();
+        return " ".repeat(2).repeat(Math.max(0, indentationLevel));
     }
 
     @Override

storage/src/test/java/org/apache/kafka/tiered/storage/utils/LocalTieredStorageOutput.java

@@ -39,7 +39,7 @@ public final class LocalTieredStorageOutput<K, V> implements LocalTieredStorageT
         this.keyDe = keyDe;
         this.valueDe = valueDe;
         // Columns length + 5 column separators.
-        output += repeatString("-", 51 + 8 + 13 + 10 + (3 * 2)) + System.lineSeparator();
+        output += "-".repeat(51 + 8 + 13 + 10 + (3 * 2)) + System.lineSeparator();
     }
 
     private String row(String file, Object offset, String record, String ident) {
@@ -54,14 +54,6 @@ public final class LocalTieredStorageOutput<K, V> implements LocalTieredStorageT
         return row("", "", "");
     }
 
-    private String repeatString(String str, int times) {
-        StringBuilder builder = new StringBuilder();
-        for (int i = 0; i < times; i++) {
-            builder.append(str);
-        }
-        return builder.toString();
-    }
-
     @Override
     public void visitTopicIdPartition(TopicIdPartition topicIdPartition) {
         currentTopic = topicIdPartition.topicPartition().topic();

streams/integration-tests/src/test/java/org/apache/kafka/streams/integration/HighAvailabilityTaskAssignorIntegrationTest.java

@@ -287,11 +287,7 @@ public class HighAvailabilityTaskAssignorIntegrationTest {
     }
 
     private static String getKiloByteValue() {
-        final StringBuilder kiloBuilder = new StringBuilder(1000);
-        for (int i = 0; i < 1000; i++) {
-            kiloBuilder.append('0');
-        }
-        return kiloBuilder.toString();
+        return "0".repeat(1000);
     }
 
     private static void assertFalseNoRetry(final boolean assertion, final String message) {

streams/src/test/java/org/apache/kafka/streams/kstream/MaterializedTest.java

@@ -100,14 +100,8 @@ public class MaterializedTest {
 
     @Test
     public void shouldThrowTopologyExceptionIfStoreNameExceedsMaxAllowedLength() {
-        final StringBuffer invalidStoreNameBuffer = new StringBuffer();
         final int maxNameLength = 249;
-
-        for (int i = 0; i < maxNameLength + 1; i++) {
-            invalidStoreNameBuffer.append('a');
-        }
-
-        final String invalidStoreName = invalidStoreNameBuffer.toString();
+        final String invalidStoreName = "a".repeat(maxNameLength + 1);
 
         final TopologyException e = assertThrows(TopologyException.class,
             () -> Materialized.as(invalidStoreName));

tools/src/main/java/org/apache/kafka/tools/ProducerPerformance.java

@@ -194,7 +194,7 @@ public class ProducerPerformance {
                 throw new IllegalArgumentException("File does not exist or empty file provided.");
             }
 
-            String[] payloadList = new String(Files.readAllBytes(path), StandardCharsets.UTF_8).split(payloadDelimiter);
+            String[] payloadList = Files.readString(path).split(payloadDelimiter);
 
             System.out.println("Number of messages read: " + payloadList.length);
 

tools/src/test/java/org/apache/kafka/tools/LeaderElectionCommandTest.java

@@ -36,7 +36,6 @@ import org.mockito.ArgumentCaptor;
 import org.mockito.MockedStatic;
 import org.mockito.Mockito;
 
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.time.Duration;
@@ -325,7 +324,7 @@ public class LeaderElectionCommandTest {
 
         String jsonString = stringifyTopicPartitions(new HashSet<>(partitions));
 
-        Files.write(file.toPath(), jsonString.getBytes(StandardCharsets.UTF_8));
+        Files.writeString(file.toPath(), jsonString);
 
         return file.toPath();
     }
@@ -333,7 +332,7 @@ public class LeaderElectionCommandTest {
     private Path tempAdminConfig(String defaultApiTimeoutMs, String requestTimeoutMs) throws Exception {
         String content = "default.api.timeout.ms=" + defaultApiTimeoutMs + "\nrequest.timeout.ms=" + requestTimeoutMs;
         java.io.File file = TestUtils.tempFile("admin-config", ".properties");
-        Files.write(file.toPath(), content.getBytes(StandardCharsets.UTF_8));
+        Files.writeString(file.toPath(), content);
         return file.toPath();
     }
 

trogdor/src/test/java/org/apache/kafka/trogdor/common/JsonUtilTest.java

@@ -26,7 +26,6 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
 
 import java.io.File;
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -62,7 +61,7 @@ public class JsonUtilTest {
         assertEquals(1, JsonUtil.objectFromCommandLineArgument("   {\"bar\": 1}   ", Foo.class).bar);
         File tempFile = TestUtils.tempFile();
         try {
-            Files.write(tempFile.toPath(), "{\"bar\": 456}".getBytes(StandardCharsets.UTF_8));
+            Files.writeString(tempFile.toPath(), "{\"bar\": 456}");
             assertEquals(456, JsonUtil.objectFromCommandLineArgument(tempFile.getAbsolutePath(), Foo.class).bar);
         } finally {
             Files.delete(tempFile.toPath());