Java核心_内省

2021-08-13 23:37:34

Java核心_内省

查看java的api，发现有一个包java.bean
咦，这个包是干什么的呢，原来，它是用来操作JavaBean对象的！

一、内省操作
①JavaBean：一种特殊的Java类
无参构造方法，每个属性提供getter和setter
/Introspector/src/yuki/core/introspector/bean/Point.java

package yuki.core.introspector.bean;

public class Point {

    private int x;
    private int y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }
    public void setX(int x) {
        this.x = x;
    }
    public int getY() {
        return y;
    }
    public void setY(int y) {
        this.y = y;
    }
}

获取设置值

用内省获取属性值与设置属性值
/Introspector/src/yuki/core/introspector/test/PointTest1

package yuki.core.introspector.test;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;

import yuki.core.introspector.bean.Point;

public class PointTest {

    /**
     * 获得point对象的getX方法的值
     * 如果用反射，需要得到x的字段名
     * 然后首字母大写，前面加get，拼成getX
     * 然后调用这个对象的方法拿到x属性
     * 这里不演示
     *
     * 如果用内省的方法，可以......
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {

        Point p = new Point(3, 4);

        String propertyName = "x";
        // x --> X --> getX --> MethodGetX
        PropertyDescriptor pd = new PropertyDescriptor(propertyName, p.getClass());
        Method methodGetX = pd.getReadMethod();
        Object retVal = methodGetX.invoke(p);
        System.out.println(retVal);

        Method methodSetX = pd.getWriteMethod();
        methodSetX.invoke(p, 7);
        System.out.println(p.getX());
    }
}

运行结果如下：

3
7

②抽取方法
使用Eclipse从代码中抽取出方法
Refractor>Extract Method...>MethodName=

/Introspector/src/yuki/core/introspector/test/PointTest2

package yuki.core.introspector.test;

import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import yuki.core.introspector.bean.Point;

public class PointTest {

    public static void main(String[] args) throws Exception {
        Point p = new Point(3, 4);

        String propertyName = "x";
        Object retVal = getProperty(p, propertyName);
        System.out.println(retVal);

        Object value = 7;
        setProperty(p, propertyName, value);
        System.out.println(p.getX());
    }

    private static void setProperty(Object p, String propertyName, Object value) throws IntrospectionException, IllegalAccessException, InvocationTargetException {
        PropertyDescriptor pd2 = new PropertyDescriptor(propertyName, p.getClass());
        Method methodSetX = pd2.getWriteMethod();
        methodSetX.invoke(p, value);
    }

    private static Object getProperty(Object p, String propertyName) throws IntrospectionException, IllegalAccessException, InvocationTargetException {
        PropertyDescriptor pd = new PropertyDescriptor(propertyName, p.getClass());
        Method methodGetX = pd.getReadMethod();
        Object retVal = methodGetX.invoke(p);
        return retVal;
    }
}

运行结果如下：

3
7

③BeanInfo对象
调用IntroSpector.getBeanInfo可以得到BeanInfo对象，
BeanInfo对象封装了把这个类当作JavaBean看的结果信息
/Introspector/src/yuki/core/introspector/test/PointTest3

package yuki.core.introspector.test;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import yuki.core.introspector.bean.Point;

public class PointTest {

    public static void main(String[] args) throws Exception {
        Point p = new Point(3, 4);

        String propertyName = "x";
        Object retVal = getProperty(p, propertyName);
        System.out.println(retVal);
    }

    private static Object getProperty(Object p, String propertyName) throws IntrospectionException, IllegalAccessException, InvocationTargetException {
        BeanInfo beanInfo = Introspector.getBeanInfo(p.getClass());
        PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
        Object retVal = null;
        for(PropertyDescriptor pd : pds){
            if(pd.getName().equals(propertyName)){
                Method methodGetX = pd.getReadMethod();
                retVal = methodGetX.invoke(p);
                break;
            }
        }
        return retVal;
    }
}

运行结果如下：

二、BeanUtils工具包操作JavaBean
①Apache提供的工具包
http://commons.apache.org/proper/commons-beanutils/download_beanutils.cgi
commons-beanutils-1.9.2-bin.zip/commons-beanutils-1.9.2.jar

报错：java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory
还需要提供日志包：commons-logging-1.1.3.jar
再次运行得到x的值为3，设置x的值为9
/Introspector/src/yuki/core/introspector/test/PointTest.java

package yuki.core.introspector.test;

import org.apache.commons.beanutils.BeanUtils;

import yuki.core.introspector.bean.Point;

public class PointTest {

    public static void main(String[] args) throws Exception {
        Point p = new Point(3, 4);

        String x = BeanUtils.getProperty(p, "x");
        System.out.println(x);

        BeanUtils.setProperty(p, "x", 9);
        System.out.println(p.getX());

        System.out.println(BeanUtils.getProperty(p, "x").getClass().getName());
    }
}

运行结果如下：

3
9
java.lang.String

字符串类型与属性类型的自动转换
但是，得到x的结果类型为字符串，但是实际值为int
因为从浏览器中获取的值是字符串，如果设置的是"9"的字符串，就会自动转换成int
而显示在网页上的值也是是字符串，所以，这样的设定提供了很大的便捷

②属性的级联操作
假设有一个属性是日期类型
类Date有一个方法，setTime(long time); 所以可以认为Date有一个time的属性
属性birth是一个复合属性，所以可以Date的毫秒值
直接获取cat.getBirth()得到的是null，这是因为没有给birth对象赋初值；
/Introspector/src/yuki/core/introspector/bean/Cat.java

package yuki.core.introspector.bean;

import java.util.Date;

public class Cat {

    private Date birth;
    private String name;
    private Integer age;

    public Cat() {}
    public Cat(Date birth) {
        this.birth = birth;
    }
    public Cat(Date birth, String name, Integer age) {
        this.birth = birth;
        this.name = name;
        this.age = age;
    }

    public Date getBirth() {
        return birth;
    }
    public void setBirth(Date birth) {
        this.birth = birth;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Cat [birth=" + birth + ", name=" + name + ", age=" + age + "]";
    }

}

/Introspector/src/yuki/core/introspector/test/CatTest.java

package yuki.core.introspector.test;

import java.util.Date;

import org.apache.commons.beanutils.BeanUtils;

import yuki.core.introspector.bean.Cat;

public class CatTest {

    public static void main(String[] args) throws Exception {
        Cat cat = new Cat();

        cat.setBirth(new Date());
        BeanUtils.setProperty(cat, "birth.time", "10001000");
        System.out.println(cat.getBirth());

        String birth_time = BeanUtils.getProperty(cat, "birth.time");
        System.out.println(birth_time);
    }
}

运行结果如下：

Thu Jan 01 10:46:41 CST 1970
10001000

③BeanUtils的函数

一个对象上的属性拷贝到另外一个对象
public static void copyProperties(Object dest, Object orig)
一个JavaBean的属性转换成Map
public static Map<String,String> describe(Object bean)
Map转换成一个JavaBean的属性
public static void populate(Object bean, Map<String,? extends Object> properties)
/Introspector/src/yuki/core/introspector/map/BeanUtilsTest.java

package yuki.core.introspector.map;

import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.beanutils.BeanUtils;

import yuki.core.introspector.bean.Cat;

public class BeanUtilsTest {

    public static void main(String[] args) throws Exception {

        //Map --> JavaBean
        Cat cat = new Cat();
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("name", "Tom");
        map.put("age", 12);
        BeanUtils.populate(cat, map);
        System.out.println(cat);

        //JavaBean --> Map
        Map<String, String> map2 = BeanUtils.describe(cat);
        for(Map.Entry<String, String> entry : map2.entrySet()){
            System.out.println(entry.getKey() + " -> " + entry.getValue());
        }

        //cat --> cat2
        Cat cat2 = new Cat(new Date(), null, 14);
        BeanUtils.copyProperties(cat2, cat);
        System.out.println(cat2);

    }

}

运行结果如下：

Cat [birth=null, name=Tom, age=12]
name -> Tom
birth -> null
class -> class yuki.core.introspector.bean.Cat
age -> 12
Cat [birth=null, name=Tom, age=12]

④PropertyUtils的函数
这个对象的函数setProperty和getProperty的类型转换是没有字符串的
/Introspector/src/yuki/core/introspector/map/PropertyUtilsTest.java

package yuki.core.introspector.map;

import org.apache.commons.beanutils.PropertyUtils;

import yuki.core.introspector.bean.Cat;

public class PropertyUtilsTest {

    public static void main(String[] args) throws Exception {

        Cat cat = new Cat();
        PropertyUtils.setProperty(cat, "age", 11);
        System.out.println(cat);

        System.out.println(PropertyUtils.getProperty(cat, "age").getClass().getName());
    }
}

运行结果如下：

Cat [birth=null, name=null, age=11]
java.lang.Integer

以上的内容参考了[张孝祥Java高新技术_内省]

三、用同一个类的对象更新这个对象的属性
一般用作表单中取得的对象更新数据库中的对象
①反射的方式
spring的 @Autowire标签可以不用写setter方法就可以实现自动编织

/Introspector/src/yuki/core/introspector/field/FieldUtil.java

package yuki.core.introspector.field;

import java.lang.reflect.Field;
import java.util.Date;

import yuki.core.introspector.bean.Cat;

public class FieldUtil {

    public static void main(String[] args) throws Exception {
        Cat c1 = new Cat(new Date(12345), "Tom", 11);
        Cat c2 = new Cat();
        FieldUtil.updateField(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(new Date(), "", null);
        FieldUtil.updateField(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(new Date(), "Gaffey", null);
        FieldUtil.updateField(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(null, "Gaffey", 13);
        FieldUtil.updateField(c1, c2);
        System.out.println(c1);
    }

    /**
     * 用同一个类的对象更新这个对象的属性
     * @param dest 目标对象，一般属数据库中取出的的对象
     * @param orig 赋值对象，一般是表单中取得的对象
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     */
    public static <T> void updateField(T dest, T orig) throws IllegalArgumentException, IllegalAccessException {
        Field[] fs = dest.getClass().getDeclaredFields();
        for(Field f : fs){
            try {
                f.setAccessible(true);
                Object val = f.get(orig);
                if(val != null && !"".equals(val)){
                    f.set(dest, val);
                }
            } finally {
                f.setAccessible(false);
            }
        }
    }
}

运行结果如下：

Cat [birth=Thu Jan 01 08:00:12 CST 1970, name=Tom, age=11]
Cat [birth=Sat Oct 18 01:56:21 CST 2014, name=Tom, age=11]
Cat [birth=Sat Oct 18 01:56:21 CST 2014, name=Gaffey, age=11]
Cat [birth=Thu Jan 01 08:00:12 CST 1970, name=Gaffey, age=13]

②内省的方式
/Introspector/src/yuki/core/introspector/field/PropertyUtil.java

package yuki.core.introspector.field;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Date;

import yuki.core.introspector.bean.Cat;

public class PropertyUtil {

    public static void main(String[] args) throws Exception {
        Cat c1 = new Cat(new Date(12345), "Tom", 11);
        Cat c2 = new Cat();
        PropertyUtil.updateProperty(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(new Date(), "", null);
        PropertyUtil.updateProperty(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(new Date(), "Gaffey", null);
        PropertyUtil.updateProperty(c1, c2);
        System.out.println(c1);

        c1 = new Cat(new Date(12345), "Tom", 11);
        c2 = new Cat(null, "Gaffey", 13);
        PropertyUtil.updateProperty(c1, c2);
        System.out.println(c1);
    }

    /**
     * 用同一个类的对象更新这个对象的属性
     * @param dest 目标对象，一般属数据库中取出的的对象
     * @param orig 赋值对象，一般是表单中取得的对象
     * @throws IntrospectionException
     * @throws InvocationTargetException
     * @throws IllegalArgumentException
     * @throws IllegalAccessException
     */
    public static <T> void updateProperty(T dest, T orig) throws IntrospectionException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        BeanInfo beanInfo = Introspector.getBeanInfo(dest.getClass());
        PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
        for(PropertyDescriptor pd : pds){
            Method read = pd.getReadMethod();
            Object val = read.invoke(orig);
            if(val != null && !"".equals(val)){
                Method write = pd.getWriteMethod();
                if(write != null)
                    write.invoke(dest, val);
            }
        }
    }
}

运行结果如下：

Cat [birth=Thu Jan 01 08:00:12 CST 1970, name=Tom, age=11]
Cat [birth=Sat Oct 18 01:57:35 CST 2014, name=Tom, age=11]
Cat [birth=Sat Oct 18 01:57:35 CST 2014, name=Gaffey, age=11]
Cat [birth=Thu Jan 01 08:00:12 CST 1970, name=Gaffey, age=13]

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kongdongyang
2014/10/18

码农公寓

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