139 lines
4.5 KiB
Markdown
139 lines
4.5 KiB
Markdown
# 日志
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## 日志框架
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# 枚举
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**一般用作信息的标记和分类**
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## 枚举的特点
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<img src="https://gitee.com/icecat2233/picture/raw/master/20260104153711421.png" alt="image-20260104153710216" style="zoom:50%;" />
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作用：
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代码优雅，可读性高，入参约束严谨
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# 类加载器
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**过程**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20260105160250925.png" alt="image-20260105160242903" style="zoom: 50%;" />
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类加载器的分类
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**双亲委派模型：**
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# 反射：
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## 如何创建类的字节码对象：
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## 反射类中的构造方法
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其中返回单个构造方法对象括号中给的参数是可变参数，给的是字节码文件参数，用来代表返回的是有参构造还是无参构造，可看下边例子
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**反射到Constructor类中后的创建对象方法**
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其中newInstance方法中的参数代表了是走的带参构造还是无参构造
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```Java
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public class Demo1 {
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public static void main(String[] args) throws Exception{
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//获取类的字节码对象
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Class<?> class1 = Class.forName("com.ice.cat.domain.Student");
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//反射构造方法对象
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Constructor<?> constructor = class1.getDeclaredConstructor(String.class,int.class);//此方法无视权限返回单个所有权限的构造方法对象
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//设置为true 表示取消访问检查
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constructor.setAccessible(true);
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//通过此方法实例化，创建对象
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Object o = constructor.newInstance("杏菜",15);
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System.out.println(o);
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}
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}
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```
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## 反射类中的成员变量：
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## 设置成员变量的方法
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例子：
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```Java
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public class Demo2 {
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public static void main(String[] args)throws Exception{
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//获取Student的字节码文件
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Class<Student> studentClass = Student.class;
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//暴力获取单个所有权限无参构造方法
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Constructor<Student> constructor = studentClass.getDeclaredConstructor();
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//取消检查权限
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constructor.setAccessible(true);
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//实例化
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Student stu1 = constructor.newInstance();
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Student stu2 = constructor.newInstance();
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//暴力反射内部成员变量
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Field name = studentClass.getDeclaredField("name");
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Field age = studentClass.getDeclaredField("age");
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//因为是暴力获取，得设置访问权限
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name.setAccessible(true);
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age.setAccessible(true);
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//通过set给成员变量赋值
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name.set(stu1,"杏菜");
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name.set(stu2,"佳树");
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age.set(stu1,15);
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age.set(stu2,13);
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System.out.println(name.get(stu1));
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System.out.println(name.get(stu2));
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}
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}
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```
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## 反射的建议：禁止暴力反射
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小知识点：Java中的泛型是假的，只有在编译期间有效
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```Java
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public class Test1 {
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//在一个泛型为Integer的集合里面添加一个字符串
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//思路：Java中的泛型是假的，只有在编译期间有效
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public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
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ArrayList<Integer> list = new ArrayList<>();
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Collections.addAll(list,1,2,3,4);
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Class<? extends ArrayList> class1 = list.getClass();
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Method add = class1.getMethod("add", Object.class);
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add.invoke(list,"hhh");
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System.out.println(list);
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}
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}
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```
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# 方法引用：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20260106153308790.png" alt="image-20260106153259853" style="zoom:50%;" />
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# Junit单元测试：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20260106153753082.png" alt="image-20260106153751296" style="zoom:50%;" />
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## 总结：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20260106154608910.png" alt="image-20260106154607624" style="zoom:50%;" /> |