java反射
1 package com.sfbest.financial.basedata.utils; 2 3 import java.lang.reflect.Constructor; 4 import java.lang.reflect.Field; 5 import java.lang.reflect.InvocationTargetException; 6 import java.lang.reflect.Method; 7 import java.lang.reflect.Modifier; 8 9 public class Main { 10 /** 11 * 为了看清楚Java反射部分代码，所有异常我都最后抛出来给虚拟机处理！ 12 * @param args 13 * @throws ClassNotFoundException 14 * @throws InstantiationException 15 * @throws IllegalAccessException 16 * @throws InvocationTargetException 17 * @throws IllegalArgumentException 18 * @throws NoSuchFieldException 19 * @throws SecurityException 20 * @throws NoSuchMethodException 21 */ 22 public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, SecurityException, NoSuchFieldException, NoSuchMethodException { 23 // TODO Auto-generated method stub 24 25 //Demo1. 通过Java反射机制得到类的包名和类名 26 /* Demo1(); 27 System.out.println("==============================================="); 28 29 //Demo2. 验证所有的类都是Class类的实例对象 30 Demo2(); 31 System.out.println("==============================================="); 32 33 //Demo3. 通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在]，无参构造 34 Demo3(); 35 System.out.println("==============================================="); 36 37 //Demo4: 通过Java反射机制得到一个类的构造函数，并实现构造带参实例对象 38 /*Demo4(); 39 System.out.println("==============================================="); 40 41 //Demo5: 通过Java反射机制操作成员变量, set 和 get 42 Demo5(); 43 System.out.println("==============================================="); 44 45 //Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等 46 Demo6(); 47 System.out.println("==============================================="); 48 49 //Demo7: 通过Java反射机制调用类中方法 50 Demo7(); 51 System.out.println("==============================================="); */ 52 53 //Demo8: 通过Java反射机制获得类加载器 54 Demo8(); 55 System.out.println("==============================================="); 56 57 } 58 59 /** 60 * Demo1: 通过Java反射机制得到类的包名和类名 61 */ 62 public static void Demo1() 63 { 64 Person person = new Person(); 65 System.out.println("Demo1: 包名: " + person.getClass().getPackage().getName() + "，" 66 + "完整类名: " + person.getClass().getName()); 67 } 68 69 /** 70 * Demo2: 验证所有的类都是Class类的实例对象 71 * @throws ClassNotFoundException 72 */ 73 public static void Demo2() throws ClassNotFoundException 74 { 75 //定义两个类型都未知的Class , 设置初值为null, 看看如何给它们赋值成Person类 76 Class<?> class1 = null; 77 Class<?> class2 = null; 78 79 //写法1, 可能抛出 ClassNotFoundException [多用这个写法] 80 class1 = Class.forName("cn.lee.demo.Person"); 81 System.out.println("Demo2:(写法1) 包名: " + class1.getPackage().getName() + "，" 82 + "完整类名: " + class1.getName()); 83 84 //写法2 85 class2 = Person.class; 86 System.out.println("Demo2:(写法2) 包名: " + class2.getPackage().getName() + "，" 87 + "完整类名: " + class2.getName()); 88 } 89 90 /** 91 * Demo3: 通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在] 92 * @throws ClassNotFoundException 93 * @throws IllegalAccessException 94 * @throws InstantiationException 95 */ 96 public static void Demo3() throws ClassNotFoundException, InstantiationException, IllegalAccessException 97 { 98 Class<?> class1 = null; 99 class1 = Class.forName("cn.lee.demo.Person"); 100 //由于这里不能带参数，所以你要实例化的这个类Person，一定要有无参构造函数哈～ 101 Person person = (Person) class1.newInstance(); 102 person.setAge(20); 103 person.setName("LeeFeng"); 104 System.out.println("Demo3: " + person.getName() + " : " + person.getAge()); 105 } 106 107 /** 108 * Demo4: 通过Java反射机制得到一个类的构造函数，并实现创建带参实例对象 109 * @throws ClassNotFoundException 110 * @throws InvocationTargetException 111 * @throws IllegalAccessException 112 * @throws InstantiationException 113 * @throws IllegalArgumentException 114 */ 115 public static void Demo4() throws ClassNotFoundException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException 116 { 117 Class<?> class1 = null; 118 Person person1 = null; 119 Person person2 = null; 120 121 class1 = Class.forName("cn.lee.demo.Person"); 122 //得到一系列构造函数集合 123 Constructor<?>[] constructors = class1.getConstructors(); 124 125 person1 = (Person) constructors[0].newInstance(); 126 person1.setAge(30); 127 person1.setName("leeFeng"); 128 129 person2 = (Person) constructors[1].newInstance(20,"leeFeng"); 130 131 System.out.println("Demo4: " + person1.getName() + " : " + person1.getAge() 132 + " , " + person2.getName() + " : " + person2.getAge() 133 ); 134 135 } 136 137 /** 138 * Demo5: 通过Java反射机制操作成员变量, set 和 get 139 * 140 * @throws IllegalAccessException 141 * @throws IllegalArgumentException 142 * @throws NoSuchFieldException 143 * @throws SecurityException 144 * @throws InstantiationException 145 * @throws ClassNotFoundException 146 */ 147 public static void Demo5() throws IllegalArgumentException, IllegalAccessException, SecurityException, NoSuchFieldException, InstantiationException, ClassNotFoundException 148 { 149 Class<?> class1 = Class.forName("cn.lee.demo.Person"); 150 Object obj = class1.newInstance(); 151 Field personNameField = class1.getDeclaredField("name"); 152 personNameField.setAccessible(true); 153 personNameField.set(obj, "胖虎先森"); 154 155 156 System.out.println("Demo5: 修改属性之后得到属性变量的值：" + personNameField.get(obj)); 157 158 } 159 160 161 /** 162 * Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等 163 * @throws ClassNotFoundException 164 */ 165 public static void Demo6() throws ClassNotFoundException 166 { 167 Class<?> class1 = null; 168 class1 = Class.forName("cn.lee.demo.SuperMan"); 169 170 //取得父类名称 171 Class<?> superClass = class1.getSuperclass(); 172 System.out.println("Demo6: SuperMan类的父类名: " + superClass.getName()); 173 174 System.out.println("==============================================="); 175 176 177 Field[] fields = class1.getDeclaredFields(); 178 for (int i = 0; i < fields.length; i++) { 179 System.out.println("类中的成员: " + fields[i]); 180 } 181 System.out.println("==============================================="); 182 183 184 //取得类方法 185 Method[] methods = class1.getDeclaredMethods(); 186 for (int i = 0; i < methods.length; i++) { 187 System.out.println("Demo6,取得SuperMan类的方法："); 188 System.out.println("函数名：" + methods[i].getName()); 189 System.out.println("函数返回类型：" + methods[i].getReturnType()); 190 System.out.println("函数访问修饰符：" + Modifier.toString(methods[i].getModifiers())); 191 System.out.println("函数代码写法： " + methods[i]); 192 } 193 194 System.out.println("==============================================="); 195 196 //取得类实现的接口,因为接口类也属于Class,所以得到接口中的方法也是一样的方法得到哈 197 Class<?> interfaces[] = class1.getInterfaces(); 198 for (int i = 0; i < interfaces.length; i++) { 199 System.out.println("实现的接口类名: " + interfaces[i].getName() ); 200 } 201 202 } 203 204 /** 205 * Demo7: 通过Java反射机制调用类方法 206 * @throws ClassNotFoundException 207 * @throws NoSuchMethodException 208 * @throws SecurityException 209 * @throws InvocationTargetException 210 * @throws IllegalAccessException 211 * @throws IllegalArgumentException 212 * @throws InstantiationException 213 */ 214 public static void Demo7() throws ClassNotFoundException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, InstantiationException 215 { 216 Class<?> class1 = null; 217 class1 = Class.forName("cn.lee.demo.SuperMan"); 218 219 System.out.println("Demo7: \n调用无参方法fly()："); 220 Method method = class1.getMethod("fly"); 221 method.invoke(class1.newInstance()); 222 223 System.out.println("调用有参方法walk(int m)："); 224 method = class1.getMethod("walk",int.class); 225 method.invoke(class1.newInstance(),100); 226 } 227 228 /** 229 * Demo8: 通过Java反射机制得到类加载器信息 230 * 231 * 在java中有三种类类加载器。[这段资料网上截取] 232 233 1）Bootstrap ClassLoader 此加载器采用c++编写，一般开发中很少见。 234 235 2）Extension ClassLoader 用来进行扩展类的加载，一般对应的是jre\lib\ext目录中的类 236 237 3）AppClassLoader 加载classpath指定的类，是最常用的加载器。同时也是java中默认的加载器。 238 * 239 * @throws ClassNotFoundException 240 */ 241 public static void Demo8() throws ClassNotFoundException 242 { 243 Class<?> class1 = null; 244 class1 =SuperMan.class; 245 String nameString = class1.getClassLoader().getClass().getName(); 246 247 System.out.println("Demo8: 类加载器类名: " + nameString); 248 } 249 250 251 252 } 253 /** 254 * 255 * @author xiaoyaomeng 256 * 257 */ 258 class Person{ 259 private int age; 260 private String name; 261 public Person(){ 262 263 } 264 public Person(int age, String name){ 265 this.age = age; 266 this.name = name; 267 } 268 269 public int getAge() { 270 return age; 271 } 272 public void setAge(int age) { 273 this.age = age; 274 } 275 public String getName() { 276 return name; 277 } 278 public void setName(String name) { 279 this.name = name; 280 } 281 } 282 283 class SuperMan extends Person implements ActionInterface 284 { 285 private boolean BlueBriefs; 286 287 public void fly() 288 { 289 System.out.println("超人会飞耶～～"); 290 } 291 292 public boolean isBlueBriefs() { 293 return BlueBriefs; 294 } 295 public void setBlueBriefs(boolean blueBriefs) { 296 BlueBriefs = blueBriefs; 297 } 298 299 @Override 300 public void walk(int m) { 301 // TODO Auto-generated method stub 302 System.out.println("超人会走耶～～走了" + m + "米就走不动了！"); 303 } 304 } 305 interface ActionInterface{ 306 public void walk(int m); 307 }
比如在代码中声明了一个域是List<String>类型的，虽然在运行时刻其类型会变成原始类型List，但是仍然可以通过反射来获取到所用的实际的类型参数。
1 Field field = Pair.class.getDeclaredField("myList"); //myList的类型是List 2 Type type = field.getGenericType(); 3 if (type instanceof ParameterizedType) { 4 ParameterizedType paramType = (ParameterizedType) type; 5 Type[] actualTypes = paramType.getActualTypeArguments(); 6 for (Type aType : actualTypes) { 7 if (aType instanceof Class) { 8 Class clz = (Class) aType; 9 System.out.println(clz.getName()); //输出java.lang.String 10 } 11 } 12 }
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