Spring PropertyEditor 相关类的模拟实现

Spring xml 配置文件中的字符串值类型是如何通过 Spring的机制以正确的数据类型注入给目标属性的？
以下主要模拟将 String 转为 int 、date 类型。

首先 Spring 是结合了 java.beans.BeanInfo 实现了属性的转换。

1、模拟的demo类

package com.jd;import java.beans.*;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.stream.Stream;public class JavaBeanDemo {    public static void main(String[] args) {        try {            BeanInfo beanInfo = Introspector.getBeanInfo(Student.class, Object.class);            PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();            Stream.of(propertyDescriptors).forEach(System.out::println);            System.out.println();            Student student = new Student();            Stream.of(propertyDescriptors).forEach(propertyDescriptor -> {                String propertyName = propertyDescriptor.getName();                if ("id".equals(propertyName)) {                    // 必须设置一下，否则会 NNP                    propertyDescriptor.setPropertyEditorClass(IdPropertyEditor.class);                    PropertyEditor propertyEditor = propertyDescriptor.createPropertyEditor(student);                    Method setIdMethod = propertyDescriptor.getWriteMethod();                    propertyEditor.addPropertyChangeListener(new SetPropertyChangeListener(student, setIdMethod));                    propertyEditor.setAsText("99");                }                if ("birth".equals(propertyName)) {                    // 必须设置一下，否则会 NNP                    propertyDescriptor.setPropertyEditorClass(DatePropertyEditor.class);                    PropertyEditor propertyEditor = propertyDescriptor.createPropertyEditor(student);                    Method setBirthMethod = propertyDescriptor.getWriteMethod();                    propertyEditor.addPropertyChangeListener(new SetPropertyChangeListener(student, setBirthMethod));                    propertyEditor.setAsText("2017-09-01 22:00:00");                }            });            System.out.println(student);        } catch (Exception e) {            e.printStackTrace();        }    }    private static class SetPropertyChangeListener implements PropertyChangeListener {        private Object bean;        private Method setWriteMethod;        public SetPropertyChangeListener(Object bean, Method setWriteMethod) {            this.bean = bean;            this.setWriteMethod = setWriteMethod;        }        @Override        public void propertyChange(PropertyChangeEvent event) {            PropertyEditor source = (PropertyEditor) event.getSource();            try {                setWriteMethod.invoke(bean, source.getValue());            } catch (IllegalAccessException e) {                e.printStackTrace();            } catch (InvocationTargetException e) {                e.printStackTrace();            }        }    }}

2、int 类型 PropertyEditor

package com.jd;import org.springframework.util.StringUtils;import java.beans.PropertyEditorSupport;public class IdPropertyEditor extends PropertyEditorSupport {    @Override    public void setAsText(String text) throws IllegalArgumentException {        if (StringUtils.hasText(text)) {            int id = Integer.valueOf(text);            setValue(id);        }    }}

3、date 类型PropertyEditor

package com.jd;import org.springframework.util.StringUtils;import java.beans.PropertyEditorSupport;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;public class DatePropertyEditor extends PropertyEditorSupport {    @Override    public void setAsText(String text) throws IllegalArgumentException {        if (StringUtils.hasText(text)) {            SimpleDateFormat simpleDateFormat = new SimpleDateFormat();            simpleDateFormat.applyPattern("yyyy-MM-dd HH:mm");            try {                Date date = simpleDateFormat.parse(text);                setValue(date);            } catch (ParseException e) {                throw new RuntimeException(e);            }        }    }}

4、Java bean

package com.jd;import java.util.Date;public class Student {    private int id;    private String name;    private int age;    private Date birth;    public Date getBirth() {        return birth;    }    public void setBirth(Date birth) {        this.birth = birth;    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    @Override    public String toString() {        return "Student{" +                "id=" + id +                ", name='" + name + '\'' +                ", age=" + age +                ", birth=" + birth +                '}';    }}