Java Introspector（内省）

POJO

public class Student {
    // 创建属性(含有 get|set 的Field)
    private String name;
    private int age;
    private Date birthday;

    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {  //age
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    // 只有 set
    public int getAbc(){  //abc
        return 10;
    }
}

内省

1. Introspector构建一个BeanInfo对象。
2. BeanInfo将一个类的所有属性进行了封装
3. 获取属性描述器
   PropertyDescriptor[] pds = bf.getPropertyDescriptors();
4. PropertyDescriptor对象：
   1. Method getReadMethod()
   获得应该用于读取属性值的方法。
   2. Method getWriteMethod()
   获得应该用于写入属性值的方法。

public class 内省 {
    @Test
    public void test1() throws Exception {
        // 将Student中的所有属性封装到BeanInfo对象中
        BeanInfo bf = Introspector.getBeanInfo(Student.class);
        // 属性描述器
        PropertyDescriptor[] pds = bf.getPropertyDescriptors();
        // System.out.println(pds.length);
        for (PropertyDescriptor pd : pds) {
            System.out.println(pd.getName());
        }
        /*
        5
        abc
        age
        birthday
        class
        name
        */
    }

    @Test
    public void test2() throws Exception {
        Student stu = new Student();
        // 得到指定的属性对象
        PropertyDescriptor pd = new PropertyDescriptor("name", Student.class);
        Method setter = pd.getWriteMethod();// 得到setter方法：setName()
        setter.invoke(stu, "tom");

        Method getter = pd.getReadMethod(); // 得到getter方法：getName()
        System.out.println(getter.invoke(stu, null));
    }

    @Test
    public void test3() throws Exception {
        Student stu = new Student();
        // 得到指定的属性对象
        PropertyDescriptor pd = new PropertyDescriptor("age", Student.class);
        Method setter = pd.getWriteMethod();// 得到setter方法：setName()
        setter.invoke(stu, 18);

        Method getter = pd.getReadMethod(); // 得到getter方法：getName()
        System.out.println(getter.invoke(stu, null));
    }
}

BeanUtils 的封装使用

public class BeanUtil {
    @Test
    public void test1() throws Exception{
        Student stu = new Student();

        BeanUtils.setProperty(stu, "name", "张三"); //给属性赋值
        String s = BeanUtils.getProperty(stu, "name");

        System.out.println(s);
    }

    @Test
    public void test2() throws Exception{
        Student stu = new Student();
        //BeanUtils默认支持8种基本数据类型，自动转换
        BeanUtils.setProperty(stu, "age", "18"); //给属性赋值
        String s = BeanUtils.getProperty(stu, "age");

        System.out.println(s);
    }

    @Test
    public void test3() throws Exception{
        Student stu = new Student();
        //注册类型转换器
        ConvertUtils.register(new DateLocaleConverter(), Date.class);
        BeanUtils.setProperty(stu, "birthday", "1990-11-12"); //给属性赋值
        String s = BeanUtils.getProperty(stu, "birthday");

        System.out.println(s);
    }

    @Test
    public void test4() throws Exception{
        Student stu = new Student();
        //注册类型转换器
        ConvertUtils.register(new Converter() {

            public Object convert(Class type, Object value) {
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
                if(value instanceof String){
                    String v = (String) value;
                    try {
                        return sdf.parse(v);
                    } catch (ParseException e) {
                        throw new RuntimeException(e);
                    }
                }
                return null;
            }
        }, Date.class);

        BeanUtils.setProperty(stu, "birthday", "1995-11-12"); //给属性赋值
        String s = BeanUtils.getProperty(stu, "birthday");

        System.out.println(s);
    }

    @Test
    public void test5() throws Exception{
        //
        Map m = new HashMap();
        m.put("name", "张三"); //key名一定要与对象中的变量名一致
        m.put("age", "18"); //key名一定要与对象中的变量名一致
        m.put("birthday", "1992-05-12"); //key名一定要与对象中的变量名一致

        Student stu = new Student();

        ConvertUtils.register(new DateLocaleConverter(), Date.class);
        BeanUtils.populate(stu, m); //将Map属性自动放到Bean中

        System.out.println(stu.getName());
    }
}