Refactored to add a way to copy JobParameters into another via builder

In a previous commit, the JobParametersBuilder was updated to include
some code from Spring Boot that handled the incrementing of
JobParameters for a previous job.  That commit brought over a private
`merge` method that is actually useful for general consumption.

This commit adds a `addJobParameters` method to the builder providing
the same functionality the `merge` method did in a public method.

spring-batch-core/src/main/java/org/springframework/batch/core/JobParametersBuilder.java

@@ -222,6 +222,19 @@ public class JobParametersBuilder {
 		return this;
 	}
 
+	/**
+	 * Copy job parameters into the current state.
+	 * @param jobParameters parameters to copy in
+	 * @return a reference to this object.
+	 */
+	public JobParametersBuilder addJobParameters(JobParameters jobParameters) {
+		Assert.notNull(jobParameters, "jobParameters must not be null");
+
+		this.parameterMap.putAll(jobParameters.getParameters());
+
+		return this;
+	}
+
 	/**
 	 * Initializes the {@link JobParameters} based on the state of the {@link Job}.  This
 	 * should be called after all parameters have been entered into the builder.
@@ -267,7 +280,10 @@ public class JobParametersBuilder {
 				nextParameters = incrementer.getNext(previousExecution.getJobParameters());
 			}
 		}
-		this.parameterMap = merge(nextParameters, this.parameterMap);
+
+		this.parameterMap = addJobParameters(nextParameters)
+								.toJobParameters()
+								.getParameters();
 		return this;
 	}
 
@@ -280,14 +296,6 @@ public class JobParametersBuilder {
 		}
 	}
 
-	private LinkedHashMap<String, JobParameter> merge(JobParameters parameters,
-			Map<String, JobParameter> additionals) {
-		Map<String, JobParameter> merged = new HashMap<>();
-		merged.putAll(parameters.getParameters());
-		merged.putAll(additionals);
-		return new LinkedHashMap<>(merged);
-	}
-
 	private boolean isStoppedOrFailed(JobExecution execution) {
 		BatchStatus status = execution.getStatus();
 		return (status == BatchStatus.STOPPED || status == BatchStatus.FAILED);

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

@@ -64,6 +64,28 @@ public class JobParametersBuilderTests {
 		this.parametersBuilder = new JobParametersBuilder(this.jobExplorer);
 	}
 
+	@Test
+	public void testAddingExistingJobParameters() {
+		JobParameters params1 = new JobParametersBuilder()
+				.addString("foo", "bar")
+				.addString("bar", "baz")
+				.toJobParameters();
+
+		JobParameters params2 = new JobParametersBuilder()
+				.addString("foo", "baz")
+				.toJobParameters();
+
+		JobParameters finalParams = new JobParametersBuilder()
+				.addString("baz", "quix")
+				.addJobParameters(params1)
+				.addJobParameters(params2)
+				.toJobParameters();
+
+		assertEquals(finalParams.getString("foo"), "baz");
+		assertEquals(finalParams.getString("bar"), "baz");
+		assertEquals(finalParams.getString("baz"), "quix");
+	}
+
 	@Test
 	public void testNonIdentifyingParameters() {
 		this.parametersBuilder.addDate("SCHEDULE_DATE", date, false);