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来源：http://www.bjsxt.com/
一、S02E213反射机制_提高反射效率、操作泛型、操作注解
反射机制性能问题
package com.test.reflection;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;import com.test.bean.User;
/*** 通过跳过安全检查，提高反射效率* 三种执行方法的效率差异比较*/
public class ReflectionRuntime {public static void test01(){User u = new User();long startTime = System.currentTimeMillis();for (int i = 0; i < 1000000000L; i++) {u.getUname();}long endTime = System.currentTimeMillis();System.out.println("普通方法调用，执行10亿次，耗时：" + (endTime-startTime) + "ms");}public static void test02() throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{User u = new User();Class clazz = u.getClass();Method m = clazz.getDeclaredMethod("getUname", null);//m.setAccessible(true);long startTime = System.currentTimeMillis();for (int i = 0; i < 1000000000L; i++) {m.invoke(u, null);}long endTime = System.currentTimeMillis();System.out.println("反射动态方法调用，执行10亿次，耗时：" + (endTime-startTime) + "ms");}public static void test03() throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{User u = new User();Class clazz = u.getClass();Method m = clazz.getDeclaredMethod("getUname", null);m.setAccessible(true);//不需要执行访问安全检查long startTime = System.currentTimeMillis();for (int i = 0; i < 1000000000L; i++) {m.invoke(u, null);}long endTime = System.currentTimeMillis();System.out.println("反射动态方法调用，跳过安全检查，执行10亿次，耗时：" + (endTime-startTime) + "ms");}public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {test01();test02();test03();}
}package com.test.bean;public class User {private int id;private int age;private String uname;//javabean必须要有无参的构造方法！public User() {}public User(int id, int age, String uname) {super();this.id = id;this.age = age;this.uname = uname;}public int getId() {return id;}public void setId(int id) {this.id = id;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}
}控制台输出
普通方法调用，执行10亿次，耗时：2168ms
反射动态方法调用，执行10亿次，耗时：60739ms
反射动态方法调用，跳过安全检查，执行10亿次，耗时：12310ms反射操作泛型(Generic)
package com.test.reflection;import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;import com.test.bean.User;/*** 通过反射获取泛型信息*/
public class GetGeneric {public void test01(Map<String,User> map,List<User> list){System.out.println("GetGeneric.test01()");}public Map<Integer,User> test02(){System.out.println("GetGeneric.test02()");return null;}public static void main(String[] args) {try {//获取指定方法参数泛型信息Method m = GetGeneric.class.getMethod("test01", Map.class, List.class);Type[] t = m.getGenericParameterTypes();for (Type paramType : t) {System.out.println("#" + paramType);if(paramType instanceof ParameterizedType){Type[] genericTypes = ((ParameterizedType) paramType).getActualTypeArguments();for (Type genericType : genericTypes) {System.out.println("泛型类型：" + genericType);}}}//获取指定方法返回值泛型信息Method m2 = GetGeneric.class.getMethod("test02", null);Type returnType = m2.getGenericReturnType();if(returnType instanceof ParameterizedType){Type[] genericTypes = ((ParameterizedType) returnType).getActualTypeArguments();for (Type genericType : genericTypes) {System.out.println("返回值，泛型类型：" + genericType);}}} catch (NoSuchMethodException e) {e.printStackTrace();} catch (SecurityException e) {e.printStackTrace();}}
}package com.test.bean;public class User {private int id;private int age;private String uname;//javabean必须要有无参的构造方法！public User() {}public User(int id, int age, String uname) {super();this.id = id;this.age = age;this.uname = uname;}public int getId() {return id;}public void setId(int id) {this.id = id;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}
}控制台输出
#java.util.Map<java.lang.String, com.test.bean.User>
泛型类型：class java.lang.String
泛型类型：class com.test.bean.User
#java.util.List<com.test.bean.User>
泛型类型：class com.test.bean.User
返回值，泛型类型：class java.lang.Integer
返回值，泛型类型：class com.test.bean.User反射操作注解(annotation)
package com.test.annotation2;import java.lang.annotation.Annotation;
import java.lang.reflect.Field;/*** 使用反射读取注解的信息，模拟处理注解信息的流程*/
public class Demo {public static void main(String[] args) {try {Class clazz = Class.forName("com.test.annotation2.SxtStudent");//获取类的所有有效注解Annotation[] annotations = clazz.getAnnotations();for (Annotation a : annotations) {System.out.println(a);}//获取类的指定的注解SxtTable st = (SxtTable) clazz.getAnnotation(SxtTable.class);System.out.println(st.value());//获取类的属性的注解Field f = clazz.getDeclaredField("sname");SxtField sxtField = f.getAnnotation(SxtField.class);System.out.println(sxtField.columnName()+"--"+sxtField.type()+"--"+sxtField.length());//根据获取的表名和字段的信息，拼出DDL语句，然后，使用JDBC执行这个SQL，在数据库中生成相关的表} catch (Exception e) {e.printStackTrace();}}
}package com.test.annotation2;@SxtTable("tb_student")
public class SxtStudent {@SxtField(columnName="id",type="int",length=10)private int id;@SxtField(columnName="sname",type="varchar",length=10)private String sname;@SxtField(columnName="age",type="int",length=3)private int age;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getStudentName() {return sname;}public void setStudentName(String studentName) {this.sname = studentName;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}package com.test.annotation2;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target(value={ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface SxtTable {String value();
}package com.test.annotation2;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target(value={ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface SxtField {String columnName();String type();int length();
}控制台输出
@com.test.annotation2.SxtTable(value=tb_student)
tb_student
sname--varchar--10这篇关于反射机制_提高反射效率_操作泛型_操作注解JAVA213的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
