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对象绑定与类型转换
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对象绑定与类型转换

类图

底层第一套转换接口与实现
classDiagram

Formatter --|> Printer
Formatter --|> Parser

class Converters {
   Set~GenericConverter~
}
class Converter

class ConversionService
class FormattingConversionService

ConversionService <|-- FormattingConversionService
FormattingConversionService o-- Converters

Printer --> Adapter1
Adapter1 --> Converters
Parser --> Adapter2
Adapter2 --> Converters
Converter --> Adapter3
Adapter3 --> Converters

<<interface>> Formatter
<<interface>> Printer
<<interface>> Parser
<<interface>> Converter
<<interface>> ConversionService
  • Printer 把其它类型转为 String
  • Parser 把 String 转为其它类型
  • Formatter 综合 Printer 与 Parser 功能
  • Converter 把类型 S 转为类型 T
  • Printer、Parser、Converter 经过适配转换成 GenericConverter 放入 Converters 集合
  • FormattingConversionService 利用其它们实现转换
 
底层第二套转换接口
classDiagram

PropertyEditorRegistry o-- "多" PropertyEditor

<<interface>> PropertyEditorRegistry
<<interface>> PropertyEditor
  • PropertyEditor 把 String 与其它类型相互转换
  • PropertyEditorRegistry 可以注册多个 PropertyEditor 对象
  • 与第一套接口直接可以通过 FormatterPropertyEditorAdapter 来进行适配
 
高层接口与实现
classDiagram
TypeConverter <|-- SimpleTypeConverter
TypeConverter <|-- BeanWrapperImpl
TypeConverter <|-- DirectFieldAccessor
TypeConverter <|-- ServletRequestDataBinder

SimpleTypeConverter --> TypeConverterDelegate
BeanWrapperImpl --> TypeConverterDelegate
DirectFieldAccessor --> TypeConverterDelegate
ServletRequestDataBinder --> TypeConverterDelegate

TypeConverterDelegate --> ConversionService
TypeConverterDelegate --> PropertyEditorRegistry

<<interface>> TypeConverter
<<interface>> ConversionService
<<interface>> PropertyEditorRegistry
  • 它们都实现了 TypeConverter 这个高层转换接口，在转换时，会用到 TypeConverter Delegate 委派ConversionService 与 PropertyEditorRegistry 真正执行转换（Facade 门面模式）
    • 首先看是否有自定义转换器, @InitBinder 添加的即属于这种 (用了适配器模式把 Formatter 转为需要的 PropertyEditor)
    • 再看有没有 ConversionService 转换
    • 再利用默认的 PropertyEditor 转换
    • 最后有一些特殊处理
  • SimpleTypeConverter 仅做类型转换
  • BeanWrapperImpl 为 bean 的属性赋值，当需要时做类型转换，走 Property
  • DirectFieldAccessor 为 bean 的属性赋值，当需要时做类型转换，走 Field
  • ServletRequestDataBinder 为 bean 的属性执行绑定，当需要时做类型转换，根据 directFieldAccess 选择走 Property 还是 Field，具备校验与获取校验结果功能

案例

非web环境

SimpleConverter

public class TestSimpleConverter {
    public static void main(String[] args) {
        // 仅有类型转换的功能
        SimpleTypeConverter typeConverter = new SimpleTypeConverter();
        Integer number = typeConverter.convertIfNecessary("13", int.class);
        Date date = typeConverter.convertIfNecessary("1999/03/04", Date.class);
        System.out.println(number);
        System.out.println(date);
    }
}
输出
13
Thu Mar 04 00:00:00 CST 1999

BeanWrapper

public class TestBeanWrapper {
    public static void main(String[] args) {
        // 利用反射原理, 为 bean 的属性赋值
        MyBean target = new MyBean();
        BeanWrapperImpl wrapper = new BeanWrapperImpl(target);
        wrapper.setPropertyValue("a", "10");
        wrapper.setPropertyValue("b", "hello");
        wrapper.setPropertyValue("c", "1999/03/04");
        System.out.println(target);
    }

    static class MyBean {
        private int a;
        private String b;
        private Date c;

        public int getA() {
            return a;
        }

        public void setA(int a) {
            this.a = a;
        }

        public String getB() {
            return b;
        }

        public void setB(String b) {
            this.b = b;
        }

        public Date getC() {
            return c;
        }

        public void setC(Date c) {
            this.c = c;
        }

        @Override
        public String toString() {
            return "MyBean{" +
                   "a=" + a +
                   ", b='" + b + '\'' +
                   ", c=" + c +
                   '}';
        }
    }
}
输出
MyBean{a=10, b='hello', c=Thu Mar 04 00:00:00 CST 1999}

FieldAccessor

public class TestFieldAccessor {
    public static void main(String[] args) {
        // 利用反射原理, 为 bean 的属性赋值
        MyBean target = new MyBean();
        DirectFieldAccessor accessor = new DirectFieldAccessor(target);
        accessor.setPropertyValue("a", "10");
        accessor.setPropertyValue("b", "hello");
        accessor.setPropertyValue("c", "1999/03/04");
        System.out.println(target);
    }

    static class MyBean {
        private int a;
        private String b;
        private Date c;
        @Override
        public String toString() {
            return "MyBean{" +
                   "a=" + a +
                   ", b='" + b + '\'' +
                   ", c=" + c +
                   '}';
        }
    }
}
MyBean{a=10, b='hello', c=Thu Mar 04 00:00:00 CST 1999}

DataBinder

默认走set方法绑定数据
public class TestDataBinder {

    public static void main(String[] args) {
        // 执行数据绑定
        MyBean target = new MyBean();
        DataBinder dataBinder = new DataBinder(target);
        MutablePropertyValues pvs = new MutablePropertyValues();
        pvs.add("a", "10");
        pvs.add("b", "hello");
        pvs.add("c", "1999/03/04");
        dataBinder.bind(pvs);
        System.out.println(target);
    }

    static class MyBean {
        private int a;
        private String b;
        private Date c;

        public int getA() {
            return a;
        }

        public void setA(int a) {
            this.a = a;
        }

        public String getB() {
            return b;
        }

        public void setB(String b) {
            this.b = b;
        }

        public Date getC() {
            return c;
        }

        public void setC(Date c) {
            this.c = c;
        }

        @Override
        public String toString() {
            return "MyBean{" +
                   "a=" + a +
                   ", b='" + b + '\'' +
                   ", c=" + c +
                   '}';
        }
    }
}
 
MyBean{a=10, b='hello', c=Thu Mar 04 00:00:00 CST 1999}
去掉set方法后
static class MyBean {
        private int a;
        private String b;
        private Date c;

        @Override
        public String toString() {
            return "MyBean{" +
                   "a=" + a +
                   ", b='" + b + '\'' +
                   ", c=" + c +
                   '}';
        }
    }
 
MyBean{a=0, b='null', c=null}
dataBinder.initDirectFieldAccess(); 开启直接字段的访问
MyBean{a=10, b='hello', c=Thu Mar 04 00:00:00 CST 1999}

web环境

ServletRequestDataBinder

public class TestServletDataBinder {

    public static void main(String[] args) {
        // web 环境下数据绑定
        MyBean target = new MyBean();
        ServletRequestDataBinder dataBinder = new ServletRequestDataBinder(target);
        MockHttpServletRequest request = new MockHttpServletRequest();
        request.setParameter("a", "10");
        request.setParameter("b", "hello");
        request.setParameter("c", "1999/03/04");

        dataBinder.bind(new ServletRequestParameterPropertyValues(request));

        System.out.println(target);
    }

    static class MyBean {
        private int a;
        private String b;
        private Date c;

        public int getA() {
            return a;
        }

        public void setA(int a) {
            this.a = a;
        }

        public String getB() {
            return b;
        }

        public void setB(String b) {
            this.b = b;
        }

        public Date getC() {
            return c;
        }

        public void setC(Date c) {
            this.c = c;
        }

        @Override
        public String toString() {
            return "MyBean{" +
                   "a=" + a +
                   ", b='" + b + '\'' +
                   ", c=" + c +
                   '}';
        }
    }
}
 
MyBean{a=10, b='hello', c=Thu Mar 04 00:00:00 CST 1999}

数据绑定工厂

ServletRequestDataBinder 的局限性

使用之前的ServletRequestDataBinder 去绑定参数无法支持特殊的数据类型，比如日期，如果输入的是自定义格式YYYY|MM|DD 
TestServletDataBinderFactory {
    public static void main(String[] args) throws Exception {
        MockHttpServletRequest request = new MockHttpServletRequest();
        request.setParameter("birthday", "1999|01|02");
        request.setParameter("address.name", "西安");

        User target = new User();
        ServletRequestDataBinder dataBinder = new ServletRequestDataBinder(target, "user");
        dataBinder.bind(new ServletRequestParameterPropertyValues(request));
        System.out.println(target);

      }

    public static class User {
        @DateTimeFormat(pattern = "yyyy|MM|dd")
        private Date birthday;
        private Address address;

        public Address getAddress() {
            return address;
        }

        public void setAddress(Address address) {
            this.address = address;
        }

        public Date getBirthday() {
            return birthday;
        }

        public void setBirthday(Date birthday) {
            this.birthday = birthday;
        }

        @Override
        public String toString() {
            return "User{" +
                   "birthday=" + birthday +
                   ", address=" + address +
                   '}';
        }
    }

    public static class Address {
        private String name;

        public String getName() {
            return name;
        }

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

        @Override
        public String toString() {
            return "Address{" +
                   "name='" + name + '\'' +
                   '}';
        }
    }
}
输出
User{birthday=null, address=Address{name='西安'}}
日期类型没有绑定上
 
使用工厂创建转换器
ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);
        factory.createBinder(new ServletWebRequest(request), target, "user")
                .bind(new ServletRequestParameterPropertyValues(request));
System.out.println(target);
 
User{birthday=null, address=Address{name='西安'}}

用 @InitBinder 转换

static class MyController {
        @InitBinder
        public void aaa(WebDataBinder dataBinder) {
            // 扩展 dataBinder 的转换器
            dataBinder.addCustomFormatter(new MyDateFormatter("用 @InitBinder 方式扩展的"));
        }
    }
自定义转换器，继承Formatter接口
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.format.Formatter;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class MyDateFormatter implements Formatter<Date> {
    private static final Logger log = LoggerFactory.getLogger(MyDateFormatter.class);
    private final String desc;

    public MyDateFormatter(String desc) {
        this.desc = desc;
    }

    @Override
    public String print(Date date, Locale locale) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy|MM|dd");
        return sdf.format(date);
    }

    @Override
    public Date parse(String text, Locale locale) throws ParseException {
        log.debug(">>>>>> 进入了: {}", desc);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy|MM|dd");
        return sdf.parse(text);
    }


}
 
public static void main(String[] args) throws Exception {
        MockHttpServletRequest request = new MockHttpServletRequest();
        request.setParameter("birthday", "1999|01|02");
        request.setParameter("address.name", "西安");

        User target = new User();
        InvocableHandlerMethod method = new InvocableHandlerMethod(new MyController(), MyController.class.getMethod("aaa", WebDataBinder.class));
        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(List.of(method), null);
        factory.createBinder(new ServletWebRequest(request), target, "user")
                .bind(new ServletRequestParameterPropertyValues(request));
        System.out.println(target);
  
    }
 
[DEBUG] 19:33:47.123 [main] com.onethink.a23.MyDateFormatter    - >>>>>> 进入了: 用 @InitBinder 方式扩展的 
User{birthday=Sat Jan 02 00:00:00 CST 1999, address=Address{name='西安'}}

ConversionService

 
FormattingConversionService service = new FormattingConversionService();
        service.addFormatter(new MyDateFormatter("用 ConversionService 方式扩展转换功能"));
        ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
        initializer.setConversionService(service);
        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, initializer);
        factory.createBinder(new ServletWebRequest(request), target, "user")
                .bind(new ServletRequestParameterPropertyValues(request));
        System.out.println(target);
[DEBUG] 19:39:23.555 [main] com.onethink.a23.MyDateFormatter    - >>>>>> 进入了: 用 ConversionService 方式扩展转换功能 
User{birthday=Sat Jan 02 00:00:00 CST 1999, address=Address{name='西安'}}
 
同时使用ConversionService和@initBinder
@initBinder优先级更高
 
InvocableHandlerMethod method = new InvocableHandlerMethod(new MyController(), MyController.class.getMethod("aaa", WebDataBinder.class));

        FormattingConversionService service = new FormattingConversionService();
        service.addFormatter(new MyDateFormatter("用 ConversionService 方式扩展转换功能"));
        ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
        initializer.setConversionService(service);
        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(List.of(method), initializer);
        // "5. 使用默认 ConversionService 转换"
        WebDataBinder dataBinder = factory.createBinder(new ServletWebRequest(request), target, "user");
        dataBinder.bind(new ServletRequestParameterPropertyValues(request));
        System.out.println(target);
[DEBUG] 19:44:19.667 [main] com.onethink.a23.MyDateFormatter    - >>>>>> 进入了: 用 @InitBinder 方式扩展的 
User{birthday=Sat Jan 02 00:00:00 CST 1999, address=Address{name='西安'}}
 
使用默认的ConversionService 不需要自定义formatter，配合 @DateTimeFormat(pattern = "yyyy|MM|dd")
springboot使用ApplicationConversionService
非springboot用DefaultConversionService
ApplicationConversionService service = new ApplicationConversionService();
        ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
        initializer.setConversionService(service);

        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, initializer);

        WebDataBinder dataBinder = factory.createBinder(new ServletWebRequest(request), target, "user");
        dataBinder.bind(new ServletRequestParameterPropertyValues(request));
        System.out.println(target);
 
User{birthday=Sat Jan 02 00:00:00 CST 1999, address=Address{name='西安'}}

泛型参数获取

class BaseDao<T> {
    T findOne() {
        return null;
    }
}

class TeacherDao extends BaseDao<Teacher> {
}
 
public class TestGenericType {
    public static void main(String[] args) {
        // 小技巧
        // 1. java api
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>");
        Type type = TeacherDao.class.getGenericSuperclass();
        System.out.println(type);

        if (type instanceof ParameterizedType parameterizedType) {
            System.out.println(parameterizedType.getActualTypeArguments()[0]);
        }

        // 2. spring api 1 单个泛型参数
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>");
        Class<?> t = GenericTypeResolver.resolveTypeArgument(TeacherDao.class, BaseDao.class);
        System.out.println(t);

        // 3. spring api 2
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>");
        System.out.println(ResolvableType.forClass(TeacherDao.class).getSuperType().getGeneric().resolve());
    }

}
 
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