java 反射性能优化

待我称王封你为后i 2022-11-18 05:52 206阅读 0赞

### 反射访问器 ###

import sun.misc.Unsafe;
    
    import java.lang.reflect.Field;
    
    /**
     * @Author JZ
     * @Date 2021/4/12 16:30
     */
    public class UnsafeFieldAccessor { 
    
        private static final Unsafe unsafe ;
    
        static { 
            try { 
                Field field = Unsafe.class.getDeclaredField("theUnsafe");
                field.setAccessible(true);
                unsafe = (Unsafe) field.get(null);
            } catch (Exception e) { 
                throw new IllegalStateException(e);
            }
        }
    
        private final long fieldOffset;
    
        public UnsafeFieldAccessor(Field field) { 
            fieldOffset = unsafe.objectFieldOffset(field);
        }
    
        public Object getObject(Object object) { 
            return unsafe.getObject(object, fieldOffset);
        }
    
        public void setObject(Object object, Object value) { 
            unsafe.putObject(object, fieldOffset, value);
        }
    
    }

### 测试 ###

import com.jz.zeus.excel.util.UnsafeFieldAccessor;
    import lombok.Data;
    import lombok.SneakyThrows;
    
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    /**
     * @Author JZ
     * @Date 2021/4/12 16:31
     */
    public class Test { 
    
        @Data
        static class T { 
            private Object obj;
        }
    
        @SneakyThrows
        public static void main(String[] args) { 
            Method getMethod = T.class.getMethod("getObj");
            Method setMethod = T.class.getMethod("setObj", Object.class);
            Field field = T.class.getDeclaredField("obj");
            field.setAccessible(true);
            UnsafeFieldAccessor accessor = new UnsafeFieldAccessor(field);
            T t = new T();
            Object v = new Object();
            int n = 10000000;
            long start;
    
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                t = new T();
                t.setObj(new Object());
                accessor.getObject(t);
            }
            System.out.printf("unsafe get: %d\n", System.currentTimeMillis() - start);
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                field.get(t);
            }
            System.out.printf("reflect get: %d\n", System.currentTimeMillis() - start);
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                getMethod.invoke(t);
            }
            System.out.printf("cache method get: %d\n", System.currentTimeMillis() - start);
    
            // -----------------------------------------------------
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                accessor.setObject(t, v);
            }
            System.out.printf("unsafe set: %d\n", System.currentTimeMillis() - start);
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                field.set(t, v);
            }
            System.out.printf("reflect set: %d\n", System.currentTimeMillis() - start);
    
            start = System.currentTimeMillis();
            for (int i = 0; i < n; i++) { 
                setMethod.invoke(t, v);
            }
            System.out.printf("cache method set: %d\n", System.currentTimeMillis() - start);
        }
    
    }