Modernize string operations

src/main/java/org/jenkins/plugins/lockableresources/LockStepExecution.java

@@ -176,8 +176,7 @@ public static void proceed(
                             @Override
                             public void expand(@NonNull EnvVars env) {
                                 final LinkedHashMap<String, String> variables = new LinkedHashMap<>();
-                                final String resourceNames =
-                                        lockedResources.keySet().stream().collect(Collectors.joining(","));
+                                final String resourceNames = String.join(",", lockedResources.keySet());
                                 variables.put(variable, resourceNames);
                                 int index = 0;
                                 for (Entry<String, List<LockableResourceProperty>> lockResourceEntry :

src/main/java/org/jenkins/plugins/lockableresources/LockableResourcesManager.java

@@ -358,9 +358,9 @@ public List<LockableResource> fromNames(final List<String> names, final boolean
 
     // ---------------------------------------------------------------------------
     private String getStack() {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         for (StackTraceElement st : Thread.currentThread().getStackTrace()) {
-            buf.append("\n" + st);
+            buf.append("\n").append(st);
         }
         return buf.toString();
     }
@@ -1213,7 +1213,7 @@ private List<LockableResource> getFreeResourcesWithLabel(
     // ---------------------------------------------------------------------------
     // for debug purpose
     private String getCauses(List<LockableResource> resources) {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         int currentSize = 0;
         for (LockableResource resource : resources) {
             String cause = resource.getLockCauseDetail();
@@ -1224,7 +1224,7 @@ private String getCauses(List<LockableResource> resources) {
                 buf.append("\n  ...");
                 break;
             }
-            buf.append("\n  " + cause);
+            buf.append("\n  ").append(cause);
 
             final String queueCause = getQueueCause(resource);
             if (!queueCause.isEmpty()) {
@@ -1237,7 +1237,7 @@ private String getCauses(List<LockableResource> resources) {
     // ---------------------------------------------------------------------------
     // for debug purpose
     private String getQueueCause(final LockableResource resource) {
-        Map<Run<?, ?>, Integer> usage = new HashMap<Run<?, ?>, Integer>();
+        Map<Run<?, ?>, Integer> usage = new HashMap<>();
 
         for (QueuedContextStruct entry : this.queuedContexts) {
 
@@ -1263,16 +1263,20 @@ private String getQueueCause(final LockableResource resource) {
             usage.put(build, count);
         }
 
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         int currentSize = 0;
         for (Map.Entry<Run<?, ?>, Integer> entry : usage.entrySet()) {
             Run<?, ?> build = entry.getKey();
             int count = entry.getValue();
 
             if (build != null && count > 0) {
                 currentSize++;
-                buf.append("\n    Queued " + count + " time(s) by build " + " " + build.getFullDisplayName() + " "
-                        + ModelHyperlinkNote.encodeTo(build));
+                buf.append("\n    Queued ")
+                        .append(count)
+                        .append(" time(s) by build ")
+                        .append(build.getFullDisplayName())
+                        .append(" ")
+                        .append(ModelHyperlinkNote.encodeTo(build));
 
                 if (currentSize >= enabledCausesCount) {
                     buf.append("\n    ...");

src/main/java/org/jenkins/plugins/lockableresources/RequiredResourcesProperty.java

@@ -236,7 +236,7 @@
             String label = Util.fixEmptyAndTrim(labelName);
             String script = Util.fixEmptyAndTrim(resourceMatchScript);
 
-            if (number == null || number.equals("") || number.trim().equals("0")) {
+            if (number == null || number.isEmpty() || number.trim().equals("0")) {
                 return FormValidation.ok();
             }
 

src/main/java/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction.java

@@ -279,14 +279,14 @@ public int getAssignedResourceAmount(String labelString) {
     // ---------------------------------------------------------------------------
     private void informPerformanceIssue() {
         String method = Thread.currentThread().getStackTrace()[2].getMethodName();
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         for (StackTraceElement st : Thread.currentThread().getStackTrace()) {
-            buf.append("\n" + st);
+            buf.append("\n").append(st);
         }
         LOGGER.warning("lockable-resources-plugin: The method "
                 + method
                 + " has been deprecated due performance issues. When you see this message, please inform plugin developers:"
-                + buf.toString());
+                + buf);
     }
 
     // ---------------------------------------------------------------------------

src/test/java/org/jenkins/plugins/lockableresources/PressureTest.java

@@ -54,10 +54,10 @@ public void pressure(final int resourcesCount) throws Exception {
         // create resources
         LOGGER.info("Create resources with labels");
         for (int i = 1; i <= resourcesCount; i++) {
-            lrm.createResourceWithLabel("resourceA_" + Integer.toString(i), "label1 label2");
-            lrm.createResourceWithLabel("resourceAA_" + Integer.toString(i), "label");
-            lrm.createResourceWithLabel("resourceAAA_" + Integer.toString(i), "label1");
-            lrm.createResourceWithLabel("resourceAAAA_" + Integer.toString(i), "(=%/!(/)?$/ HH( RU))");
+            lrm.createResourceWithLabel("resourceA_" + i, "label1 label2");
+            lrm.createResourceWithLabel("resourceAA_" + i, "label");
+            lrm.createResourceWithLabel("resourceAAA_" + i, "label1");
+            lrm.createResourceWithLabel("resourceAAAA_" + i, "(=%/!(/)?$/ HH( RU))");
         }
 
         // define groovy script used by our test jobs
@@ -137,14 +137,14 @@ public void pressure(final int resourcesCount) throws Exception {
         // create more resources until the first job has been started
         LOGGER.info("Create more resources");
         for (int i = 1; i <= resourcesCount; i++) {
-            lrm.createResourceWithLabel("resourceB_" + Integer.toString(i), "label1");
+            lrm.createResourceWithLabel("resourceB_" + i, "label1");
         }
 
         // create jenkins nodes. All shall be mirrored to resources
         LOGGER.info("Create jenkins nodes");
         for (int i = 1; i <= nodesCount; i++) {
             j.createSlave("AgentAAA_" + i, "label label1 label2", null);
-            lrm.createResourceWithLabel("resourceC_" + Integer.toString(i), "label1");
+            lrm.createResourceWithLabel("resourceC_" + i, "label1");
             j.createSlave("AGENT_BBB_" + i, null, null);
         }
 
@@ -156,7 +156,7 @@ public void pressure(final int resourcesCount) throws Exception {
         // create more resources until the first job has been started
         LOGGER.info("Additional resources");
         for (int i = 1; i <= resourcesCount; i++) {
-            lrm.createResourceWithLabel("resourceD_" + Integer.toString(i), "label1");
+            lrm.createResourceWithLabel("resourceD_" + i, "label1");
         }
 
         // create more jenkins nodes to make more chaos