[Chore] Enhances code readability and maintainability (#17894)

Author: Mrhs121

dolphinscheduler-task-plugin/dolphinscheduler-task-java/src/main/java/org/apache/dolphinscheduler/plugin/task/java/JavaTask.java

@@ -39,7 +39,7 @@
 
 import org.apache.commons.lang3.StringUtils;
 
-import java.io.File;
+import java.nio.file.Paths;
 import java.util.Map;
 
 import lombok.extern.slf4j.Slf4j;
@@ -138,7 +138,7 @@ protected String buildJarCommand() {
                 .getResourceAbsolutePathInLocal();
         StringBuilder builder = new StringBuilder();
         builder.append(getJavaCommandPath())
-                .append("java").append(Constants.SPACE)
+                .append(Constants.SPACE)
                 .append(javaParameters.getJvmArgs().trim()).append(Constants.SPACE)
                 .append(buildResourcePath()).append(Constants.SPACE)
                 .append("-jar").append(Constants.SPACE)
@@ -167,7 +167,7 @@ protected String buildNormalJarCommand() {
         }
         StringBuilder builder = new StringBuilder();
         builder.append(getJavaCommandPath())
-                .append("java").append(Constants.SPACE)
+                .append(Constants.SPACE)
                 .append(javaParameters.getJvmArgs().trim()).append(Constants.SPACE)
                 .append(buildResourcePath()).append(Constants.SPACE)
                 .append(mainJarName).append(Constants.SPACE)
@@ -221,7 +221,7 @@ protected String buildResourcePath() {
      * @return String
      **/
     private String getJavaCommandPath() {
-        return JAVA_HOME_VAR + File.separator + "bin" + File.separator;
+        return Paths.get(JAVA_HOME_VAR, "bin", "java").toString();
     }
 
     private String parseParameter(String script) {