Demonstration of JMH and StringBuilder/StringBuffer performance - original blog at http://alblue.bandlem.com/2016/04/jmh-stringbuffer-stringbuilder.html

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>string-benchmark</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>
    <name>StringBenchmark</name>
    <prerequisites>
        <maven>3.0</maven>
    </prerequisites>
    <dependencies>
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-core</artifactId>
            <version>${jmh.version}</version>
        </dependency>
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-generator-annprocess</artifactId>
            <version>${jmh.version}</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <jmh.version>1.12</jmh.version>
        <javac.target>1.6</javac.target>
        <uberjar.name>benchmarks</uberjar.name>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <compilerVersion>${javac.target}</compilerVersion>
                    <source>${javac.target}</source>
                    <target>${javac.target}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.2</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <finalName>${uberjar.name}</finalName>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>org.openjdk.jmh.Main</mainClass>
                                </transformer>
                            </transformers>
                            <filters>
                                <filter>
                                    <artifact>*:*</artifact>
                                    <excludes>
                                        <exclude>META-INF/*.SF</exclude>
                                        <exclude>META-INF/*.DSA</exclude>
                                        <exclude>META-INF/*.RSA</exclude>
                                    </excludes>
                                </filter>
                            </filters>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
        <pluginManagement>
            <plugins>
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>2.5</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>2.4</version>
                </plugin>
                <plugin>
                    <artifactId>maven-javadoc-plugin</artifactId>
                    <version>2.9.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>2.6</version>
                </plugin>
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.3</version>
                </plugin>
                <plugin>
                    <artifactId>maven-source-plugin</artifactId>
                    <version>2.2.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.17</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

StringBenchmark.java

// Move this file to src/main/java in order to run with Maven
//
package org.sample;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Param;
//import org.openjdk.jmh.annotations.CompilerControl;
//import org.openjdk.jmh.annotations.CompilerControl.Mode;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;

@State(Scope.Benchmark)
//@CompilerControl(Mode.EXCLUDE)
public class StringBenchmark {
	private String from = "Alex";
	private String to = "Readers";
	private String subject = "Benchmarking with JMH";

	@Param({"16"})
	private int size;
	
	@Benchmark
	public String testEmptyBuffer() {
		StringBuffer buffer = new StringBuffer();
		return buffer.toString();
	}

	@Benchmark
	public String testEmptyBuilder() {
		StringBuilder builder = new StringBuilder();
		return builder.toString();
	}

	@Benchmark
	public String testEmptyLiteral() {
		return "";
	}

	@Benchmark
	public String testHelloWorldBuilder() {
		StringBuilder builder = new StringBuilder();
		builder.append("Hello");
		builder.append("World");
		return builder.toString();
	}

	@Benchmark
	public String testHelloWorldBuffer() {
		StringBuffer buffer = new StringBuffer();
		buffer.append("Hello");
		buffer.append("World");
		return buffer.toString();
	}

	@Benchmark
	public String testEmailBuilderSimple() {
		StringBuilder builder = new StringBuilder(size);
		builder.append("From");
		builder.append(from);
		builder.append("To");
		builder.append(to);
		builder.append("Subject");
		builder.append(subject);
		return builder.toString();

	}

	@Benchmark
	public String testEmailBufferSimple() {
		StringBuffer buffer = new StringBuffer(size);
		buffer.append("From");
		buffer.append(from);
		buffer.append("To");
		buffer.append(to);
		buffer.append("Subject");
		buffer.append(subject);
		return buffer.toString();
	}

	@Benchmark
	public String testEmailBuilderConcat() {
		StringBuilder builder = new StringBuilder(size);
		builder.append("From" + from);
		builder.append("To" + to);
		builder.append("Subject" + subject);
		return builder.toString();
	}

	@Benchmark
	public String testEmailBufferConcat() {
		StringBuffer buffer = new StringBuffer(size);
		buffer.append("From" + from);
		buffer.append("To" + to);
		buffer.append("Subject" + subject);
		return buffer.toString();
	}

	@Benchmark
	public String testEmailBuilderChain() {
		return new StringBuilder(size).append("From").append(from).append("To").append(to).append("Subject")
				.append(subject).toString();
	}

	@Benchmark
	public String testEmailBufferChain() {
		return new StringBuffer(size).append("From").append(from).append("To").append(to).append("Subject")
				.append(subject).toString();
	}

	@Benchmark
	public String testEmailLiteral() {
		return "From" + from + "To" + to + "Subject" + subject;
	}

}

JFYI: http://openjdk.java.net/jeps/280

If you download this gist to test, you'll need to make a directory src/main/java and then move the source file in there in order to run it. The original blog post corresponding to this gist is at http://alblue.bandlem.com/2016/04/jmh-stringbuffer-stringbuilder.html