[Java] Automatically clean up temp files. (#5507)

* Remove unused code

* Auto clean up temp files

* refine

* fix

* print warning

* fix

java/test/src/main/java/org/ray/api/test/WordCountTest.java

@@ -1,74 +0,0 @@
-package org.ray.api.test;
-
-import java.io.FileNotFoundException;
-import java.util.Arrays;
-import java.util.List;
-import org.ray.api.Ray;
-import org.ray.api.RayObject;
-import org.ray.api.annotation.RayRemote;
-import org.ray.runtime.util.FileUtil;
-import org.testng.Assert;
-
-/**
- * given a directory of document files on each "machine", we would like to count the appearance of
- * some word.
- */
-public class WordCountTest {
-
-  @RayRemote
-  public static List<String> getMachineList() {
-    return Arrays.asList("A", "B", "C");
-  }
-
-  @RayRemote
-  public static Integer countWord(String machine, String word) {
-
-    String log;
-    try {
-      log = FileUtil.readResourceFile("mapreduce/" + machine + ".log");
-    } catch (FileNotFoundException e) {
-      e.printStackTrace();
-      log = "";
-    }
-    log = log.toLowerCase();
-    int start = 0;
-    int count = 0;
-    while (true) {
-      if (start >= log.length()) {
-        break;
-      }
-      int index = log.indexOf(word, start);
-      if (index == -1) {
-        break;
-      }
-      start = index + word.length();
-      count++;
-    }
-    return count;
-  }
-
-  @RayRemote
-  public static Integer sum(Integer a, Integer/*TODO modify int to Integer in ASM hook*/ b) {
-    return a + b;
-  }
-
-  //@Test
-  public void test() {
-    int sum = mapReduce();
-    Assert.assertEquals(sum, 143);
-  }
-
-  public int mapReduce() {
-    RayObject<List<String>> machines = Ray.call(WordCountTest::getMachineList);
-    RayObject<Integer> total = null;
-    for (String machine : machines.get()) {
-      RayObject<Integer> wordcount = Ray.call(WordCountTest::countWord, machine, "ray");
-      if (total == null) {
-        total = wordcount;
-      } else {
-        total = Ray.call(WordCountTest::sum, total, wordcount);
-      }
-    }
-    return total.get();
-  }
-}