一、例子1：
1 package com.cy.test.thread; 2 3 4 import java.util.ArrayList; 5 import java.util.List; 6 import java.util.concurrent.CountDownLatch; 7 import java.util.concurrent.ExecutorService; 8 import java.util.concurrent.Executors; 9 10 public class TestMultiThread { 11 /** 12 * n = 核心數*2 + 1 13 */ 14 private static ExecutorService pool = Executors.newFixedThreadPool(5); 15 16 /** 17 * 1.模擬，使用多線程，找到每個學生的老師名字，並且打印出來。 18 * @param args 19 */ 20 public static void main(String[] args) { 21 long begin = System.currentTimeMillis(); 22 23 List<String> studentList = new ArrayList<>(); 24 studentList.add("zhangsan"); 25 studentList.add("lisi"); 26 studentList.add("wangwu"); 27 28 try { 29 CountDownLatch latch = new CountDownLatch(studentList.size()); 30 doFindTeacher(studentList, latch); 31 latch.await(); 32 } catch (InterruptedException e) { 33 e.printStackTrace(); 34 } 35 36 System.out.println("執行完畢，耗時：" + (System.currentTimeMillis() - begin) + "ms"); 37 pool.shutdown(); 38 } 39 40 private static void doFindTeacher(List<String> studentList, CountDownLatch latch) { 41 for(String student : studentList){ 42 pool.execute(() -> { 43 System.out.println("開始處理學生:" + student); 44 //模擬查數據庫...等操作，查找學生的老師 45 try { 46 Thread.sleep(3000); 47 } catch (InterruptedException e) { 48 e.printStackTrace(); 49 } 50 System.out.println("teacher: " + student + "'s teacher"); 51 52 latch.countDown(); 53 }); 54 } 55 } 56 }
console：
開始處理學生:zhangsan
開始處理學生:lisi
開始處理學生:wangwu
teacher: lisi's teacher
teacher: zhangsan's teacher
teacher: wangwu's teacher
執行完畢，耗時：3081ms
二、例子2：
1 package com.cy.test.thread; 2 3 4 import java.util.ArrayList; 5 import java.util.List; 6 import java.util.concurrent.CountDownLatch; 7 import java.util.concurrent.ExecutorService; 8 import java.util.concurrent.Executors; 9 10 public class TestMultiThread2 { 11 private static int minProcessCnt = 1; 12 private static int poolSize = 5; 13 private static ExecutorService pool = Executors.newFixedThreadPool(poolSize); 14 15 /** 16 * 1.模擬，使用多線程，找到每個學生的老師名字，並且打印出來。 17 * @param args 18 */ 19 public static void main(String[] args) { 20 long begin = System.currentTimeMillis(); 21 22 List<String> studentList = new ArrayList<>(); 23 studentList.add("zhangsan"); 24 studentList.add("lisi"); 25 studentList.add("wangwu"); 26 27 int perCnt = studentList.size() / poolSize; //每個線程處理的數量 28 int step = Math.max(perCnt, minProcessCnt); //每個線程處理的數量，按照step切割list 29 int latchNum = (studentList.size() + step - 1) / step; //處理次數 (和分頁計算方法一樣：pageCount = (totalCount + pageSize - 1)/pageSize ) 30 CountDownLatch latch = new CountDownLatch(latchNum); 31 32 //切割studentList，分批查詢 33 try { 34 for (int i = 0, start = 0; i < latchNum; i++) { 35 if(i == latchNum - 1){ 36 doFindTeacher(studentList.subList(start, studentList.size()), latch); 37 }else{ 38 doFindTeacher(studentList.subList(start, start+step), latch); 39 start = start + step; 40 } 41 } 42 43 latch.await(); 44 } catch (InterruptedException e) { 45 e.printStackTrace(); 46 } 47 48 System.out.println("執行完成，耗時：" + (System.currentTimeMillis() - begin) + "ms"); 49 50 pool.shutdown(); 51 } 52 53 private static void doFindTeacher(List<String> studentList, CountDownLatch latch){ 54 pool.execute(() -> { 55 try{ 56 for(String student : studentList){ 57 System.out.println("開始處理學生:" + student); 58 59 //模擬查數據庫...等操作，查找學生的老師 60 Thread.sleep(3000); 61 System.out.println("teacher: " + student + "'s teacher"); 62 } 63 }catch (Exception e){ 64 e.printStackTrace(); 65 }finally { 66 latch.countDown(); 67 } 68 }); 69 } 70 71 72 }
開始處理學生:wangwu
開始處理學生:zhangsan
開始處理學生:lisi
teacher: zhangsan's teacher
teacher: wangwu's teacher
teacher: lisi's teacher
執行完成，耗時：3094ms
三、例子3:
1 package com.cy.test.thread; 2 3 4 import java.util.ArrayList; 5 import java.util.List; 6 import java.util.concurrent.ExecutorService; 7 import java.util.concurrent.Executors; 8 import java.util.concurrent.FutureTask; 9 10 public class TestMultiThread3 { 11 private static int minProcessCnt = 1; 12 private static int poolSize = 5; 13 private static ExecutorService pool = Executors.newFixedThreadPool(poolSize); 14 15 /** 16 * 1.模擬，使用多線程，找到每個學生的老師名字 17 * 2.將老師們的名字返回，並且輸出 18 * @param args 19 */ 20 public static void main(String[] args) { 21 long begin = System.currentTimeMillis(); 22 23 List<String> studentList = new ArrayList<>(); 24 studentList.add("zhangsan"); 25 studentList.add("lisi"); 26 studentList.add("wangwu"); 27 28 int size = studentList.size(); 29 int perCnt = size / poolSize; 30 int step = Math.max(perCnt, minProcessCnt); 31 int pollCount = (size + step - 1) / step; // 列表循環次數 32 33 List<FutureTask<List<String>>> taskList = new ArrayList<>(); 34 for (int i = 0; i < pollCount; i++) { 35 final int start = step * i; 36 final int end = (i == pollCount - 1) ? size : step * (i + 1); 37 FutureTask<List<String>> task = new FutureTask<>(() -> { 38 return doFindTeacher(studentList, start, end); 39 }); 40 taskList.add(task); 41 pool.execute(task); 42 } 43 44 //拿到返回結果 45 List<String> teacherList = new ArrayList<>(); 46 try { 47 for (FutureTask<List<String>> futureTask : taskList) { 48 List<String> list = futureTask.get(); 49 teacherList.addAll(list); 50 } 51 }catch (Exception e){ 52 e.printStackTrace(); 53 } 54 55 System.out.println(teacherList); 56 57 System.out.println("TestMultiThread3 執行完成，耗時：" + (System.currentTimeMillis() - begin) + "ms"); 58 pool.shutdown(); 59 } 60 61 62 private static List<String> doFindTeacher(List<String> studentList, int start, int end) throws InterruptedException { 63 List<String> teacherList = new ArrayList<>(); 64 for(int j=start; j<end; j++){ 65 String student = studentList.get(j); 66 System.out.println("開始處理學生:" + student); 67 68 //模擬查數據庫...等操作，查找學生的老師 69 Thread.sleep(3000); 70 String teacher = student + "'s teacher"; 71 teacherList.add(teacher); 72 } 73 return teacherList; 74 } 75 }
console:
1 開始處理學生:zhangsan 2 開始處理學生:wangwu 3 開始處理學生:lisi 4 [zhangsan's teacher, lisi's teacher, wangwu's teacher] 5 TestMultiThread3 執行完成，耗時：3080ms