fix CodeNarc issues

src/main/groovy/com/google/protobuf/gradle/GenerateProtoTask.groovy

@@ -29,6 +29,8 @@
  */
 package com.google.protobuf.gradle
 
+import static java.nio.charset.StandardCharsets.US_ASCII
+
 import com.google.common.base.Preconditions
 import com.google.common.collect.ImmutableList
 import groovy.transform.CompileDynamic
@@ -64,8 +66,6 @@ import org.gradle.util.ConfigureUtil
 import javax.annotation.Nullable
 import javax.inject.Inject
 
-import static java.nio.charset.StandardCharsets.US_ASCII
-
 /**
  * The task that compiles proto files into Java files.
  */
@@ -79,7 +79,7 @@ public abstract class GenerateProtoTask extends DefaultTask {
   // Extra command line length when added an additional argument on Windows.
   // Two quotes and a space.
   static final int CMD_ARGUMENT_EXTRA_LENGTH = 3
-  private static final JAR_SUFFIX = ".jar"
+  private static final String JAR_SUFFIX = ".jar"
 
   // include dirs are passed to the '-I' option of protoc.  They contain protos
   // that may be "imported" from the source protos, but will not be compiled.
@@ -156,6 +156,20 @@ public abstract class GenerateProtoTask extends DefaultTask {
   @Internal("Handled as input via getDescriptorSetOptionsForCaching()")
   final DescriptorSetOptions descriptorSetOptions = new DescriptorSetOptions()
 
+  private static boolean createNewScriptFile(File outputFile) throws IOException {
+    if (!outputFile.getParentFile().isDirectory() && !outputFile.getParentFile().mkdirs()) {
+      throw new IOException("unable to make directories for file: " + outputFile.getCanonicalPath())
+    }
+    return true
+  }
+
+  private static void finalizeScriptFile(File outputFile) throws IOException {
+    if (!outputFile.setExecutable(true)) {
+      outputFile.delete()
+      throw new IOException("unable to set file as executable: " + outputFile.getCanonicalPath())
+    }
+  }
+
   // protoc allows you to prefix comma-delimited options to the path in
   // the --*_out flags, e.g.,
   // - Without options: --java_out=/path/to/output
@@ -668,16 +682,16 @@ public abstract class GenerateProtoTask extends DefaultTask {
    */
   private String createJarTrampolineScript(String jarAbsolutePath) {
     assert jarAbsolutePath.endsWith(JAR_SUFFIX)
-    final boolean isWindows = isWindows()
+    boolean isWindows = isWindows()
     File scriptExecutableFile = new File("${project.buildDir}/scripts/" +
-            jarAbsolutePath.substring(0, jarAbsolutePath.length() - JAR_SUFFIX.length()) + "-trampoline." +
+            jarAbsolutePath[0..(jarAbsolutePath.length() - JAR_SUFFIX.length())] + "-trampoline." +
             (isWindows ? "bat" : "sh"))
     try {
       if (createNewScriptFile(scriptExecutableFile)) {
         // Rewrite the trampoline file unconditionally (even if it already exists) in case the dependency or versioning
         // changes we don't need to detect the delta (and the file content is cheap to re-generate).
         new FileOutputStream(scriptExecutableFile).withCloseable { execOutputStream ->
-          final String trampoline = isWindows ?
+          String trampoline = isWindows ?
                   "@ECHO OFF\r\njava -jar ${jarAbsolutePath} %*\r\n" :
                   "#!/bin/sh\nexec java -jar ${jarAbsolutePath} \"\$@\"\n"
           execOutputStream.write(trampoline.getBytes(US_ASCII))
@@ -686,22 +700,8 @@ public abstract class GenerateProtoTask extends DefaultTask {
       }
       logger.info("Resolved artifact jar: ${jarAbsolutePath}. Created trampoline file: ${scriptExecutableFile}")
       return scriptExecutableFile.path
-    } catch (Exception e) {
+    } catch (IOException e) {
       throw new GradleException("Unable to generate trampoline for .jar protoc plugin", e)
     }
   }
-
-  private static boolean createNewScriptFile(File outputFile) throws IOException {
-    if (!outputFile.getParentFile().isDirectory() && !outputFile.getParentFile().mkdirs()) {
-      throw new IOException("unable to make directories for file: " + outputFile.getCanonicalPath())
-    }
-    return true
-  }
-
-  private static void finalizeScriptFile(File outputFile) throws IOException {
-    if (!outputFile.setExecutable(true)) {
-      outputFile.delete()
-      throw new IOException("unable to set file as executable: " + outputFile.getCanonicalPath())
-    }
-  }
 }