使用java8中的Optional API解决nullPointException问题

今天和大家一起使用java8中的optional api解决nullpointexception,

先来看一段代码：

 public class car {
  private insurance insurance;
  public insurance getinsurance() {
return insurance;
  }
 }


 public class insurance {
  private string name;
  public string getname() {
return name;
  }
 }


 public class person {
  private car car;
  public car getcar() {
return car;
  }
 }

 public string getcarinsurancename(person p){
  return p.getcar().getinsurance().getname();
 }

这个getcarinsurancename()方法一看就知道可能有nullpointexception

通常我们这样处理：

public string getcarinsurancename(person p){
  if(p!=null){
 car car = p.getcar();
 if(car!=null){
 insurane insurance = car.getinsurance();
 if(insurance!=null){
 return insurance.getname();
 }
 }
  }
  return "unknow";
}

public class person {
 private optional car;
 public optional getcar() {
  return car;
 }
}

public class car {
 private optional insurance;
 public optional getinsurance() {
  return insurance;
 }
}

public class insurance {
 private string name;
 public string getname() {
  return name;
 }
}

 public string getcarinsurancename(optional person) {
  return person.flatmap(person::getcar)
.flatmap(car::getinsurance)
.map(insurance::getname)
.orelse("unknown");
}

一脸懵逼有没有？好的大王,不管你有没有被征服，反正我是被臣妾是要开始

娓娓道来了。

上面的getcarinsurancename方法的几个关键点：

1：使用lambda表达式(不会的请恶补上篇文章)

2：使用java.util.optional对person类中的car类和car类中的insurance类包装

3：使用java.util.optional 中流式api处理数据(类似rxjava或者java.util.steam)

偷偷的把optional类实例方法截了图

optional构造函数

1：空值optional

optional optcar = optional.empty();

2：非空值optional，传空抛异常

optional optcar = optional.of(car);

3：可接受null的optional

optional optcar = optional.ofnullable(car);

使用map从optional中取值和转换值

optional optinsurance = optional.ofnullable(insurance);

optional name = optinsurance.map(insurance::getname);

使用flatmap转换optional

 

optional optcar= person.flatmap(person::getcar);

optional = optcar.flatmap(car::getinsurance)

map和flatmap区别：

optional> car = optperson.map(person::getcar);

optional car1 = optperson.flatmap(person::getcar);

ifpresent：如果值存在就会执行回调，否则什么也不干

optcar.ifpresent(car::getinsurance);

ispresent：值存在返回true，否则false

boolean = optcar.ispresent;

orelse:有值则返回，否则返回一个默认值

string name = optcar.map(insurance::getname)

.orelse("unknown");

andthen,再来个filter的例子

 @requiresapi(api = build.version_codes.n)
 public static void main(string[] args) {
  properties properties = new properties();
  properties.setproperty("a", "5");
  properties.setproperty("b", "-1");
  properties.setproperty("c", "true");
  system.out.println(readduration(properties,"a"));
  system.out.println(readduration(properties,"b"));
  system.out.println(readduration(properties,"c"));
  optionalint.of(1).
 }
 @requiresapi(api = build.version_codes.n)
 public static int readduration(properties properties, string name) {
  return optional.ofnullable(properties.getproperty(name))
 .flatmap(s -> parsestring(s))
 .filter(i -> i > 10)
 .orelse(0);
 }

 @requiresapi(api = build.version_codes.n)
 public static  optional parsestring(string s) {
  optional optionalint;
  try {
optionalint = optional.of(integer.parseint(s));
  } catch (numberformatexception e) {
optionalint = optional.empty();
  }
  return optionalint;
 }

好了，通过上面的这些例子可以帮助我们更优雅的处理nullpointexception,祝福各位撸的愉快