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 +
'}';
}
}