Properties
加载defaults.properties文件
defaults.properties内容如下
lastname=Smith
获取properties属性（defaults.properties文件和TestController文件置于同级目录）
try (InputStream bundledResource = TestController.class.getResourceAsStream("defaults.properties")) {
Properties defaults = new Properties();
defaults.load(bundledResource);
return defaults;
} catch (IOException e) {
throw new UncheckedIOException( "defaults.properties not properly packaged" + " with application", e);
}
写Properties到xml文件
Properties prop = new Properties();
prop.setProperty("name", "Steve");
prop.setProperty("color", "green");
prop.setProperty("age", "23");
File file = new File("C:\Users\26401\Desktop\defaults.properties");
if (!file.exists()){
file.createNewFile();
}
prop.storeToXML(new FileOutputStream(file), "testing properties with xml");
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
<comment>testing properties with xml</comment>
<entry key="color">green</entry>
<entry key="name">Steve</entry>
<entry key="age">23</entry>
</properties>
读Properties从xml文件
Properties prop = new Properties();
File file = new File("C:\Users\26401\Desktop\defaults.properties");
if (file.exists()){
prop.loadFromXML(new FileInputStream(file));
for (String name : prop.stringPropertyNames()){
System.out.println(name + "=" + prop.getProperty(name));
}
}else {
System.err.println("Error: No file found at: " + file);
}
Lambda表达式
自定义
Lambda表达式只能用于函数式接口
函数式接口只能包含一个抽象方法，可以有多个default和static方法，可以有多个重写对象的方法
@FunctionalInterface
interface MyFunctionalInterface {
void fn();
}
MyFunctionalInterface mfi = () -> System.out.println("函数式接口");
mfi.fn();
等价于
MyFunctionalInterface mfi = new MyFunctionalInterface() {
@Override
public void fn() {
System.out.println("函数式接口");
}
};
内置
Predicate<String> p = o -> o.isEmpty(); // 返回值类型必须是布尔值
Function<String, Boolean> f = o -> o.isEmpty(); // 返回值类型可以自定义
Consumer<String> c = o -> System.out.println(o); // 返回值类型为void
c.accept("没有返回值");
sort方法中使用Lambada
原始写法
List<Integer> list = new ArrayList<>();
list.add(3);
list.add(1);
list.add(2);
Collections.sort(list, new Comparator<Integer>(){
public int compare(Integer b, Integer l){
return b.compareTo(l);
}
}); // [1,2,3]
Lambada写法
Collections.sort(list, (b, l) -> b.compareTo(l));
或者
Collections.sort(list, Comparator.comparing(Integer::valueOf));
序列化
文件序列化
public class SerialClass implements Serializable {
private static final long serialVersionUID = 1L;
}
Gson序列化
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>
public class User {
private Integer id;
private String name;
public User(Integer id, String name) {
this.id = id;
this.name = name;
}
getter...
setter...
}
// 序列化成json
User user = new User(1, "小李");
Gson gson = new Gson();
String json = gson.toJson(user);
// 反序列化
User userCopy = gson.fromJson(json, User.class);
Jackson序列化
依赖
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.6</version>
</dependency>
json字符串转对象
ObjectMapper objectMapper = new ObjectMapper();
User outputObject = objectMapper.readValue( "{"id":"1","name":"小叶"}", User.class);
outputObject.getName();
@JsonIgnoreProperties(ignoreUnknown = true) // 忽视反序列化遇到的不认识的属性
public class User {
...
}
对象转字符串
User user = new User(1, "小李");
ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(user);
Comparable和Comparator
Comparable对象排序
public class User implements Comparable<User> {
private Integer id;
private String name;
public User(Integer id, String name) {
this.id = id;
this.name = name;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getId() {
return id;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
@Override
public boolean equals(Object o) {
if (! (o instanceof User)) return false;
User p = (User)o;
return id.equals(p.id) && name.equals(p.name);
}
@Override
public int hashCode() {
return Objects.hash(id, name);
}
@Override
public int compareTo(User other) {
int idCompare = id.compareTo(other.id);
if (idCompare != 0) {
return idCompare;
} else {
return id.compareTo(other.id);
}
}
}
List<User> list = Arrays.asList(new User(2, "小李"), new User(3, "小李"), new User(1, "小李"));
Collections.sort(list);
Comparator对象排序
List<User> list = Arrays.asList(new User(2, "小李"), new User(3, "小张"), new User(1, "小王"));
Collections.sort(list, new Comparator<User>() {
@Override
public int compare(User u1, User u2) {
return u1.getId().compareTo(u2.getId());
}
});
Collections.sort(list,(u1, u2) -> {
return u1.getId().compareTo(u2.getId());
});
Collections.sort(list,Comparator.comparing(User::getId).thenComparing(User::getName));
结语
本文章是java成神的系列文章之一
如果你想知道，但是本文没有的，请下方留言
我会第一时间总结出来并发布填充到本文