接口性能优化指南、函数式接口案例、JDK9-JDK13新特性

清疚 2023-01-13 13:59 27阅读 0赞

## 一、接口性能优化指南 ##

1.代码是不是渣？ 代码逻辑梳理与重构，去掉不必要的逻辑处理和外部查询

2.SQL是不是烂？所写SQL是否缺乏优化，比如涉及Full Scan全表扫描

3.需要进程缓存？ 进程缓存：EhCache LoadingCache Caffeine

4.需要远程缓存？ Redis，MemCache

## 二、函数式接口案例 ##

@FunctionalInterface
    public interface BiFunction<T,U,R> { 
        R apply(T t,U u);
    }
    
    @FunctionalInterface
    public interface Consumer<T> { 
        void accept(T t);
    }

@SneakyThrows
    public static void main(String[] args) { 
         System.out.println(operator(10,21,(a,b)->a+b));
         System.out.println(operator(10,2,(a,b)->a-b));
         System.out.println(operator(8,4,(a,b)->a*b));
         System.out.println(operator(10,2,(a,b)->a/b));
         Consumer<String> consumer = obj -> { 
              System.out.println("发送短信" + obj);
         };
         consumer.accept("8888888");
         send("11111111@qq.com", obj->{ 
              System.out.println("发送邮件" + obj);
        });
    }

方法：

public static Integer operator(Integer a, Integer b, BiFunction<Integer, Integer, Integer> bf){ 
         return bf.apply(a, b);
    }
    
    private static void send(String emailAndPhone, Consumer<String> consumer){ 
         consumer.accept(emailAndPhone);
    }

## 三、JDK9-JDK13新特性 ##

1.`jshell`

从java9开始，jdk引⼊了交互式 REPL（`Read-Eval-Print-Loop`，读取-求值-输出-循环）  
官⽅⽂档：[https://docs.oracle.com/en/java/javase/12/jshell/introduction-jshell.html\#GUID-63  
0F27C8-1195-4989-9F6B-2C51D46F52C8][https_docs.oracle.com_en_java_javase_12_jshell_introduction-jshell.html_GUID-63 0F27C8-1195-4989-9F6B-2C51D46F52C8]

2.增强`try-with-resource`

public static void main(String[] args) throws Exception { 
            String path = "/Desktop/t.txt";
            test(path);
        }
        private static void test(String filepath) throws FileNotFoundException { 
            OutputStream out = new FileOutputStream(filepath);
            try (out) { 
                out.write((filepath + "java").getBytes());
            } catch (Exception e) { 
                e.printStackTrace();
            }
        }

3.创建只读集合

List<String> list = List.of("SpringBoot", "SpringCloud");
                System.out.println(list);
        Set<String> set = Set.of("Mysql", "Linux", "Git");
        System.out.println(set);
        Map<String, String> map = Map.of("key1", "key2");
        System.out.println(map);

4.局部变量推断`var`

//根据推断为 字符串类型
     var strVar = "springboot";
     System.out.println(strVar instanceof String);
    
     //根据10L 推断long 类型
     var longVar = 10L;
     //根据 true推断 boolean 类型
     var flag = true;
     //var flag = Boolean.valueOf("true");
     //System.out.println(flag instanceof Boolean);
     // 推断 ArrayList<String>
     var listVar = new ArrayList<String>();
     System.out.println(listVar instanceof ArrayList);
    
     // 推断 Stream<String>
     var streamVar = Stream.of("aa", "bb", "cc");
     System.out.println(streamVar instanceof Stream)

5.`jdk11`后运⾏java程序(本地不会⽣成class⽂件)

public class Main { 
    	 public static void main(String[] args) throws Exception { 
    	 String text = "测试";
    	 //String类新增repeat(int num) ⽅法，⽤于字符串循环输出
    	 System.out.println(text.repeat(2));
    	 }
    }

6.增强`switch`表达式  
使⽤箭头函数，不⽤声明`break`,会⾃动终⽌，⽀持多个值匹配,使⽤逗号分隔

public void testNewSwitch(int i){ 
            switch(i){ 
                case 0 -> { 
                    System.out.println("zero");
                    System.out.println("这是多⾏语句");
                }
                case 1,11,111 -> System.out.println("one");
                case 2 -> System.out.println("two");
                default -> System.out.println("default");
            }
        }

[https_docs.oracle.com_en_java_javase_12_jshell_introduction-jshell.html_GUID-63 0F27C8-1195-4989-9F6B-2C51D46F52C8]: https://docs.oracle.com/en/java/javase/12/jshell/introduction-jshell.html#GUID-63%200F27C8-1195-4989-9F6B-2C51D46F52C8