BATCH-2407 Use StringBuilder instead of StringBuffer

With Java 1.5 StringBuilder is preferred over StringBuffer for single
threaded access as is has less overhead.

This is evidenced by the class comment of StringBuffer and Effective
Java 2nd Edition Item 67: Avoid excessive synchronization.

> The StringBuilder class should generally be used in preference to
> this one, as it supports all of the same operations but it is faster,
> as it performs no synchronization.

 - replace StringBuffer with StringBuilder where possible

Issue: BATCH-2407

spring-batch-core/src/test/java/org/springframework/batch/core/JobParametersTests.java

@@ -157,9 +157,9 @@ public class JobParametersTests {
 	public void testToStringOrder() {
 
 		Map<String, JobParameter> props = parameters.getParameters();
-		StringBuffer stringBuilder = new StringBuffer();
+		StringBuilder stringBuilder = new StringBuilder();
 		for (Entry<String, JobParameter> entry : props.entrySet()) {
-			stringBuilder.append(entry.toString() + ";");
+			stringBuilder.append(entry.toString()).append(";");
 		}
 
 		String string1 = stringBuilder.toString();
@@ -177,9 +177,9 @@ public class JobParametersTests {
 		JobParameters testProps = new JobParameters(parameterMap);
 
 		props = testProps.getParameters();
-		stringBuilder = new StringBuffer();
+		stringBuilder = new StringBuilder();
 		for (Entry<String, JobParameter> entry : props.entrySet()) {
-			stringBuilder.append(entry.toString() + ";");
+			stringBuilder.append(entry.toString()).append(";");
 		}
 		String string2 = stringBuilder.toString();
 

spring-batch-core/src/test/java/org/springframework/batch/core/repository/dao/JdbcJobInstanceDaoTests.java

@@ -79,7 +79,7 @@ public class JdbcJobInstanceDaoTests extends AbstractJobInstanceDaoTests {
 	public void testHexing() throws Exception {
 		MessageDigest digest = MessageDigest.getInstance("MD5");
 		byte[] bytes = digest.digest("f78spx".getBytes("UTF-8"));
-		StringBuffer output = new StringBuffer();
+		StringBuilder output = new StringBuilder();
 		for (byte bite : bytes) {
 			output.append(String.format("%02x", bite));
 		}

spring-batch-core/src/test/java/org/springframework/batch/core/repository/dao/JdbcStepExecutionDaoTests.java

@@ -49,7 +49,7 @@ public class JdbcStepExecutionDaoTests extends AbstractStepExecutionDaoTests {
 	@Test
 	public void testTruncateExitDescription() {
 
-		StringBuffer sb = new StringBuffer();
+		StringBuilder sb = new StringBuilder();
 		for (int i = 0; i < 100; i++) {
 			sb.append("too long exit description");
 		}

spring-batch-core/src/test/java/test/jdbc/datasource/DataSourceInitializer.java

@@ -135,10 +135,10 @@ public class DataSourceInitializer implements InitializingBean {
 	}
 
 	private String stripComments(List<String> list) {
-		StringBuffer buffer = new StringBuffer();
+		StringBuilder buffer = new StringBuilder();
 		for (String line : list) {
 			if (!line.startsWith("//") && !line.startsWith("--")) {
-				buffer.append(line + "\n");
+				buffer.append(line).append("\n");
 			}
 		}
 		return buffer.toString();