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import java.lang.reflect.Constructor;
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import java.lang.reflect.Field;
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import java.lang.reflect.Modifier;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* 反射工具类
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*
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*/
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    public class ReflectionUtil {
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        private ReflectionUtil() {
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            throw new AssertionError();
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        }
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/**
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* 通过反射取对象指定字段(属性)的值
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* @param target 目标对象
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* @param fieldName 字段的名字
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* @throws 如果取不到对象指定字段的值则抛出异常
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* @return 字段的值
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*/
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    public static Object getValue(Object target, String fieldName) {
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        Class<?> clazz = target.getClass();
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        String[] fs = fieldName.split("\\.");
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        try {
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            for(int i = 0; i < fs.length - 1; i++) {
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                Field f = clazz.getDeclaredField(fs[i]);
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                f.setAccessible(true);
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                target = f.get(target);
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                clazz = target.getClass();
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            }
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            Field f = clazz.getDeclaredField(fs[fs.length - 1]);
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            f.setAccessible(true);
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            return f.get(target);
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        }
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        catch (Exception e) {
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            throw new RuntimeException(e);
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        }
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    }
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/**
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* 通过反射给对象的指定字段赋值
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* @param target 目标对象
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* @param fieldName 字段的名称
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* @param value 值
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*/
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    public static void setValue(Object target, String fieldName, Object value) {
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        Class<?> clazz = target.getClass();
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        String[] fs = fieldName.split("\\.");
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        try {
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            for(int i = 0; i < fs.length - 1; i++) {
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                Field f = clazz.getDeclaredField(fs[i]);
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                f.setAccessible(true);
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                Object val = f.get(target);
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                if(val == null) {
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                    Constructor<?> c =
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                        f.getType().getDeclaredConstructor();
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                    c.setAccessible(true);
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                    val = c.newInstance();
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                    f.set(target, val);
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                }
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                target = val;
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                clazz = target.getClass();
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            }
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            Field f = clazz.getDeclaredField(fs[fs.length - 1]);
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            f.setAccessible(true);
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            f.set(target, value);
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        }
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        catch (Exception e) {
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            throw new RuntimeException(e);
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        }
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    }
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}

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import java.lang.reflect.Method;
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class MethodInvokeTest {
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    public static void main(String[] args) throws Exception {
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        String str = "hello";
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        Method m = str.getClass().getMethod("toUpperCase");
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        System.out.println(m.invoke(str)); // HELLO
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    }
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}