Java反射機制-PPT

注意：PPT來源於“https://www.bilibili.com/video/BV1p4411P7V3?p=6”。

 

 

 

 

 

 

 

 

   

 

 

 

 

    

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    @Test
    public void classLoaderTest() throws ClassNotFoundException {

        //1.獲取系統類加載器
        ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
        System.out.println(systemClassLoader);

        //2.獲取系統類加載器的父類加載器，也即擴展類加載器
        ClassLoader systemClassLoaderParent = systemClassLoader.getParent();
        System.out.println(systemClassLoaderParent);

        //3.獲取擴展類加載器的父類加載器：跟加載器(用c/c++編寫，裝載java平臺核心庫：rt.jar)
        ClassLoader parent = systemClassLoaderParent.getParent();
        System.out.println(parent);

        //4.測試用戶自己定義的類使用哪個類加載器加載進內存
        ClassLoader classLoader = Class.forName("com.wind.ssm.controller.StudentController").getClassLoader();
        System.out.println(classLoader);

        //5.測試JDK內置的類使用哪個類加載器加載進內存
        classLoader = Class.forName("java.lang.Object").getClassLoader();
        System.out.println(classLoader);

        //6.獲取系統類加載器可以加載的路徑
        String property = System.getProperty("java.class.path");
        System.out.println(property);

        //7.類加載機制：雙親委派機制

        /**
         * /Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar:
         * /Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-rt.jar:
         * /Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit5-rt.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/charsets.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/deploy.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/dnsns.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jaccess.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/localedata.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/nashorn.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunec.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/zipfs.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/javaws.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jce.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfr.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfxswt.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jsse.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/management-agent.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/plugin.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/resources.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/rt.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/ant-javafx.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/dt.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/javafx-mx.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/jconsole.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/packager.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/sa-jdi.jar:
         * /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/tools.jar:
         * /Users/cmm/codes/ssm-project/target/test-classes:/Users/cmm/codes/ssm-project/target/classes:
         * /Users/cmm/.m2/repository/org/springframework/spring-web/5.2.5.RELEASE/spring-web-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-core/5.2.5.RELEASE/spring-core-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-jcl/5.2.5.RELEASE/spring-jcl-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-beans/5.2.5.RELEASE/spring-beans-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-context/5.2.5.RELEASE/spring-context-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-context-support/5.2.5.RELEASE/spring-context-support-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-aop/5.2.5.RELEASE/spring-aop-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-aspects/5.2.5.RELEASE/spring-aspects-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/aspectj/aspectjweaver/1.9.5/aspectjweaver-1.9.5.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-expression/5.2.5.RELEASE/spring-expression-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-tx/5.2.5.RELEASE/spring-tx-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-test/5.2.5.RELEASE/spring-test-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-webmvc/5.2.5.RELEASE/spring-webmvc-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/javax/servlet/javax.servlet-api/4.0.0-b07/javax.servlet-api-4.0.0-b07.jar:
         * /Users/cmm/.m2/repository/jstl/jstl/1.2/jstl-1.2.jar:
         * /Users/cmm/.m2/repository/org/mybatis/mybatis/3.4.6/mybatis-3.4.6.jar:
         * /Users/cmm/.m2/repository/org/mybatis/mybatis-spring/2.0.3/mybatis-spring-2.0.3.jar:
         * /Users/cmm/.m2/repository/mysql/mysql-connector-java/8.0.13/mysql-connector-java-8.0.13.jar:
         * /Users/cmm/.m2/repository/com/google/protobuf/protobuf-java/3.6.1/protobuf-java-3.6.1.jar:
         * /Users/cmm/.m2/repository/org/springframework/spring-jdbc/5.2.5.RELEASE/spring-jdbc-5.2.5.RELEASE.jar:
         * /Users/cmm/.m2/repository/com/alibaba/druid/1.1.18/druid-1.1.18.jar:/Users/cmm/.m2/repository/junit/junit/4.13/junit-4.13.jar:
         * /Users/cmm/.m2/repository/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar:
         * /Users/cmm/.m2/repository/com/google/code/gson/gson/2.8.5/gson-2.8.5.jar:
         * /Users/cmm/.m2/repository/com/google/guava/guava/23.0/guava-23.0.jar:
         * /Users/cmm/.m2/repository/com/google/code/findbugs/jsr305/1.3.9/jsr305-1.3.9.jar:
         * /Users/cmm/.m2/repository/com/google/errorprone/error_prone_annotations/2.0.18/error_prone_annotations-2.0.18.jar:
         * /Users/cmm/.m2/repository/com/google/j2objc/j2objc-annotations/1.1/j2objc-annotations-1.1.jar:
         * /Users/cmm/.m2/repository/org/codehaus/mojo/animal-sniffer-annotations/1.14/animal-sniffer-annotations-1.14.jar:
         * /Users/cmm/.m2/repository/org/apache/commons/commons-collections4/4.4/commons-collections4-4.4.jar:
         * /Users/cmm/.m2/repository/org/apache/commons/commons-lang3/3.8.1/commons-lang3-3.8.1.jar:
         * /Users/cmm/.m2/repository/org/projectlombok/lombok/1.18.10/lombok-1.18.10.jar:
         * /Users/cmm/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar:
         * /Users/cmm/.m2/repository/ch/qos/logback/logback-core/1.2.3/logback-core-1.2.3.jar:
         * /Users/cmm/.m2/repository/log4j/log4j/1.2.17/log4j-1.2.17.jar:
         * /Users/cmm/.m2/repository/org/slf4j/slf4j-api/1.7.30/slf4j-api-1.7.30.jar:
         * /Users/cmm/.m2/repository/org/slf4j/slf4j-log4j12/1.7.25/slf4j-log4j12-1.7.25.jar:
         * /Users/cmm/Library/Caches/IntelliJIdea2018.1/captureAgent/debugger-agent.jar
         */
    }

 

 

 

  

 

 

 

 

package com.wind.ssm.serviceProcessor;

import java.lang.annotation.*;
import java.lang.reflect.Field;

/**
 * @Date: 2020/6/6 19:08
 * @Description:
 */
public class AnnotationTest {

    //功能：使用反射技術操作註解
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {

        Class c1 = Class.forName("com.wind.ssm.serviceProcessor.StudentOne");

        //通過反射獲取類的註解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        //獲取類註解的value的值
        TableAnnotation tableAnnotation = (TableAnnotation) c1.getAnnotation(TableAnnotation.class);
        String value = tableAnnotation.value();
        System.out.println(value);

        //獲取類指定的註解
        Field name = c1.getDeclaredField("name");
        FiledAnnotation filedAnnotation = name.getAnnotation(FiledAnnotation.class);
        System.out.println(filedAnnotation.columnName());
        System.out.println(filedAnnotation.type());
        System.out.println(filedAnnotation.length());
    }
}


@TableAnnotation("db_student")
class StudentOne {

    @FiledAnnotation(columnName = "db_id", type = "int", length = 10)
    private int id;
    @FiledAnnotation(columnName = "db_age", type = "int", length = 10)
    private int age;
    @FiledAnnotation(columnName = "db_name", type = "varchar", length = 3)
    private String name;

    public StudentOne() {
    }

    public StudentOne(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    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 getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "StudentOne{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}


//類名的註解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface TableAnnotation {
    String value();
}


//屬性的註解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FiledAnnotation {
    String columnName();

    String type();

    int length();
}