Improve code perfomance (time complexity) and readability

Author: JeanDeboutGat

webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java

@@ -545,7 +545,7 @@ protected CollectorPipeline getCollectorPipeline() {
     public <T> T get(String url) {
         List<String> urls = WMCollections.newArrayList(url);
         List<T> resultItemses = getAll(urls);
-        if (resultItemses != null && resultItemses.size() > 0) {
+        if (resultItemses != null && !resultItemses.isEmpty()) {
             return resultItemses.get(0);
         } else {
             return null;

webmagic-core/src/main/java/us/codecraft/webmagic/selector/AbstractSelectable.java

@@ -91,7 +91,7 @@ public Selectable replace(String regex, String replacement) {
     }
 
     public String getFirstSourceText() {
-        if (getSourceTexts() != null && getSourceTexts().size() > 0) {
+        if (getSourceTexts() != null && !getSourceTexts().isEmpty()) {
             return getSourceTexts().get(0);
         }
         return null;
@@ -104,6 +104,6 @@ public String toString() {
 
     @Override
     public boolean match() {
-        return getSourceTexts() != null && getSourceTexts().size() > 0;
+        return getSourceTexts() != null && !getSourceTexts().isEmpty();
     }
 }