Java反射初探123456789

牛逼的框架都反射，不要问我为什么，因为我也不知道

可能是因为生成了class文件没法实例化，所以只能反射创建对象，但是在spring中，ioc就是反射实现的控制反转

看Spring4.x企业级开发实战  自己写的  第一个是Person类

package com.smart.reflect;

/**
 * @program: chapter3
 * @description: Entity
 * @author: Sunshine
 * @create: 2020-12-25 15:34
 */
public class Person {
    private String name;
    private String nipples;
    private int hight;

    public Person() {
    }

    public Person(String name, String nipples, int hight) {
        this.name = name;
        this.nipples = nipples;
        this.hight = hight;
    }

    public void introduce () {
        System.out.println("name:"+ name+"; nipples:" + nipples +";hight:"+ hight );
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getNipples() {
        return nipples;
    }

    public void setNipples(String nipples) {
        this.nipples = nipples;
    }

    public int getHight() {
        return hight;
    }

    public void setHight(int hight) {
        this.hight = hight;
    }
}

package com.smart.reflect;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

/**
 * @program: chapter3
 * @description: 测试反射
 * @author: Sunshine
 * @create: 2020-12-25 15:39
 */
public class ReflectTest {
    public static Person initByDefaultConst() throws  Throwable {
        //1 类加载器获取对象
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Class clazz = loader.loadClass("com.smart.reflect.Person");
        //2 获取类的默认构造器对象 ，通过它实例化Person
        Constructor cons = clazz.getDeclaredConstructor((Class<?>[]) null);
        Person person = (Person) cons.newInstance();

        //3 通过反射方法设置（属性）

        Method setName = clazz.getMethod("setName", String.class);
　　　　　　// 这里才是真正的射入属性 当然得有前面的铺垫，要不直接射不太行，你说呢？
        setName.invoke(person, "兔宝宝");

        Method setNipples = clazz.getMethod("setNipples", String.class);
        setNipples.invoke(person, "pink");

        Method setHignt = clazz.getMethod("setHight", int.class);
        setHignt.invoke(person, 170);

        return person;
    }

    public static void main(String[] args) {
        try {
            Person p = initByDefaultConst();
            p.introduce();
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }
    }
}
红色的方法对应的jdk源码

/**
     * Returns a {@code Constructor} object that reflects the specified
     * constructor of the class or interface represented by this
     * {@code Class} object.  The {@code parameterTypes} parameter is
     * an array of {@code Class} objects that identify the constructor's
     * formal parameter types, in declared order.
     *
     * If this {@code Class} object represents an inner class
     * declared in a non-static context, the formal parameter types
     * include the explicit enclosing instance as the first parameter.
     *
     * @param parameterTypes the parameter array
     * @return  The {@code Constructor} object for the constructor with the
     *          specified parameter list
     * @throws  NoSuchMethodException if a matching method is not found.
     * @throws  SecurityException
     *          If a security manager, <i>s</i>, is present and any of the
     *          following conditions is met:
     *
     *          <ul>
     *
     *          <li> the caller's class loader is not the same as the
     *          class loader of this class and invocation of
     *          {@link SecurityManager#checkPermission
     *          s.checkPermission} method with
     *          {@code RuntimePermission("accessDeclaredMembers")}
     *          denies access to the declared constructor
     *
     *          <li> the caller's class loader is not the same as or an
     *          ancestor of the class loader for the current class and
     *          invocation of {@link SecurityManager#checkPackageAccess
     *          s.checkPackageAccess()} denies access to the package
     *          of this class
     *
     *          </ul>
     *
     * @since JDK1.1
     */
    @CallerSensitive
    public Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)
        throws NoSuchMethodException, SecurityException {
        checkMemberAccess(Member.DECLARED, Reflection.getCallerClass(), true);
        return getConstructor0(parameterTypes, Member.DECLARED);
    }

其实就是获取当前的这个Person类的默认的构造函数，了解的差不多就行了，别逮到一个类就往死点jdk   深入是深入了   出不来不是白给么？

下面这个图片就是借花献佛以下，下面也说了   newInsrtance（）就是实例化对象用的

 类装载器 CLassLoader

懒得打字  直接看图 

类装载找类字节，虚机建类象组件
类加载装虚机中，需要通过下几步

查找导入类文件，校验准备和解析
校验类文件数据，是否准确不掺假
准备阶段很关键，要给静态配空间
解析阶段可以选，符号引用变直引

初始化阶段不拉胯，静态系列初始化




　　　　　　　　　　　　JVM

ClassLoader　　　　　　ExtClassLoader　　　　AppClassLoader

　　

 ClassLoader loader = Thread.currentThread().getContextClassLoader();
        System.out.println("current Loader" + loader);
        System.out.println("baba Loader" + loader.getParent());
        System.out.println("yeye Loader" + loader.getParent().getParent());




"C:Program FilesJavajdk1.8.0_152injava.exe" "-javaagent:E:ideaIntelliJ IDEA 2020.2.4libidea_rt.jar=57015:E:ideaIntelliJ IDEA 2020.2.4in" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_152jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_152jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_152jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_152jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_152jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_152jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_152jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_152jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_152jrelibext
ashorn.jar;C:Program FilesJavajdk1.8.0_152jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_152jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_152jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_152jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_152jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_152jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_152jrelibjce.jar;C:Program FilesJavajdk1.8.0_152jrelibjfr.jar;C:Program FilesJavajdk1.8.0_152jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_152jrelibjsse.jar;C:Program FilesJavajdk1.8.0_152jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_152jrelibplugin.jar;C:Program FilesJavajdk1.8.0_152jrelib
esources.jar;C:Program FilesJavajdk1.8.0_152jrelib
t.jar;C:UsersAdministratorDesktopspring4.xwangpanchapter3	argetclasses;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-web1.3.3.RELEASEspring-boot-starter-web-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter1.3.3.RELEASEspring-boot-starter-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot1.3.3.RELEASEspring-boot-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-autoconfigure1.3.3.RELEASEspring-boot-autoconfigure-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-logging1.3.3.RELEASEspring-boot-starter-logging-1.3.3.RELEASE.jar;D:ToolsForDev
epositorychqoslogbacklogback-classic1.1.5logback-classic-1.1.5.jar;D:ToolsForDev
epositorychqoslogbacklogback-core1.1.5logback-core-1.1.5.jar;D:ToolsForDev
epositoryorgslf4jslf4j-api1.7.16slf4j-api-1.7.16.jar;D:ToolsForDev
epositoryorgslf4jjcl-over-slf4j1.7.16jcl-over-slf4j-1.7.16.jar;D:ToolsForDev
epositoryorgslf4jjul-to-slf4j1.7.16jul-to-slf4j-1.7.16.jar;D:ToolsForDev
epositoryorgslf4jlog4j-over-slf4j1.7.16log4j-over-slf4j-1.7.16.jar;D:ToolsForDev
epositoryorgyamlsnakeyaml1.16snakeyaml-1.16.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-tomcat1.3.3.RELEASEspring-boot-starter-tomcat-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgapache	omcatembed	omcat-embed-logging-juli8.0.32	omcat-embed-logging-juli-8.0.32.jar;D:ToolsForDev
epositoryorgapache	omcatembed	omcat-embed-websocket8.0.32	omcat-embed-websocket-8.0.32.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-validation1.3.3.RELEASEspring-boot-starter-validation-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorghibernatehibernate-validator5.2.4.Finalhibernate-validator-5.2.4.Final.jar;D:ToolsForDev
epositoryjavaxvalidationvalidation-api1.1.0.Finalvalidation-api-1.1.0.Final.jar;D:ToolsForDev
epositoryorgjbossloggingjboss-logging3.3.0.Finaljboss-logging-3.3.0.Final.jar;D:ToolsForDev
epositorycomfasterxmlclassmate1.1.0classmate-1.1.0.jar;D:ToolsForDev
epositorycomfasterxmljacksoncorejackson-databind2.6.5jackson-databind-2.6.5.jar;D:ToolsForDev
epositorycomfasterxmljacksoncorejackson-annotations2.6.5jackson-annotations-2.6.5.jar;D:ToolsForDev
epositorycomfasterxmljacksoncorejackson-core2.6.5jackson-core-2.6.5.jar;D:ToolsForDev
epositoryorgspringframeworkspring-web4.2.5.RELEASEspring-web-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkspring-aop4.2.5.RELEASEspring-aop-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryaopallianceaopalliance1.0aopalliance-1.0.jar;D:ToolsForDev
epositoryorgspringframeworkspring-beans4.2.5.RELEASEspring-beans-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkspring-context4.2.5.RELEASEspring-context-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkspring-webmvc4.2.5.RELEASEspring-webmvc-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkspring-expression4.2.5.RELEASEspring-expression-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-jdbc1.3.3.RELEASEspring-boot-starter-jdbc-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgapache	omcat	omcat-jdbc8.0.32	omcat-jdbc-8.0.32.jar;D:ToolsForDev
epositoryorgapache	omcat	omcat-juli8.0.32	omcat-juli-8.0.32.jar;D:ToolsForDev
epositoryorgspringframeworkspring-jdbc4.2.5.RELEASEspring-jdbc-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkspring-tx4.2.5.RELEASEspring-tx-4.2.5.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-starter-actuator1.3.3.RELEASEspring-boot-starter-actuator-1.3.3.RELEASE.jar;D:ToolsForDev
epositoryorgspringframeworkootspring-boot-actuator1.3.3.RELEASEspring-boot-actuator-1.3.3.RELEASE.jar;D:ToolsForDev
epositorymysqlmysql-connector-java5.1.38mysql-connector-java-5.1.38.jar;D:ToolsForDev
epositoryorgapache	omcatembed	omcat-embed-core8.0.32	omcat-embed-core-8.0.32.jar;D:ToolsForDev
epositoryorgapache	omcatembed	omcat-embed-el8.0.32	omcat-embed-el-8.0.32.jar;D:ToolsForDev
epositoryjavaxservletjstl1.2jstl-1.2.jar;D:ToolsForDev
epositoryorgspringframeworkspring-core4.2.5.RELEASEspring-core-4.2.5.RELEASE.jar" com.smart.reflect.ReflectTest
name:兔宝宝; nipples:pink;hight:170

当前加载器
current Loadersun.misc.Launcher$AppClassLoader@18b4aac2
当前加载器的爹

baba Loadersun.misc.Launcher$ExtClassLoader@33c7353a
当前加载器的爷爷

yeye Loadernull

Process finished with exit code 0

 

 

 这个费点劲   还得启动 
用这个省事

package com.smart.utils;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.CodeSource;
import java.security.ProtectionDomain;

/**
 * tools to find which jar does the class come from 
 * @author : chenxh
 * @date: 16-04-0
 */
public class ClassLocationUtils {

    /**
     * find the location of the class come from
     * @param cls
     * @return
     */
    public static String where(final Class cls) {
        if (cls == null)throw new IllegalArgumentException("null input: cls");
        URL result = null;
        final String clsAsResource = cls.getName().replace('.', '/').concat(".class");
        final ProtectionDomain pd = cls.getProtectionDomain();
        if (pd != null) {
            final CodeSource cs = pd.getCodeSource();
            if (cs != null) result = cs.getLocation();
            if (result != null) {
                if ("file".equals(result.getProtocol())) {
                    try {
                        if (result.toExternalForm().endsWith(".jar") ||
                                result.toExternalForm().endsWith(".zip"))
                            result = new URL("jar:".concat(result.toExternalForm())
                                    .concat("!/").concat(clsAsResource));
                        else if (new File(result.getFile()).isDirectory())
                            result = new URL(result, clsAsResource);
                    }
                    catch (MalformedURLException ignore) {}
                }
            }
        }
        if (result == null) {
            final ClassLoader clsLoader = cls.getClassLoader();
            result = clsLoader != null ?
                    clsLoader.getResource(clsAsResource) :
                    ClassLoader.getSystemResource(clsAsResource);
        }
        return result.toString();
    }

}

自己试了一下   嘿  您猜怎么着   还真好使

file:/C:/Users/Administrator/Desktop/spring4.x/wangpan/chapter3/target/classes/com/smart/reflect/Person.class

 

 

新鲜刺激的东西永远都有，玩之前掂量掂量自己几斤几两
【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/banxianer/p/14190177.html