聊聊Spring中的数据绑定 --- WebDataBinder、ServletRequestDataBinder、WebBindingInitializer...【享学Spring】

// @since 1.2
public class WebDataBinder extends DataBinder {

	// 此字段意思是：字段标记  比如name -> _name
	// 这对于HTML复选框和选择选项特别有用。
	public static final String DEFAULT_FIELD_MARKER_PREFIX = "_";
	// !符号是处理默认值的，提供一个默认值代替空值~~~
	public static final String DEFAULT_FIELD_DEFAULT_PREFIX = "!";
	
	@Nullable
	private String fieldMarkerPrefix = DEFAULT_FIELD_MARKER_PREFIX;
	@Nullable
	private String fieldDefaultPrefix = DEFAULT_FIELD_DEFAULT_PREFIX;
	// 默认也会绑定空的文件流~
	private boolean bindEmptyMultipartFiles = true;

	// 完全沿用父类的两个构造~~~
	public WebDataBinder(@Nullable Object target) {
		super(target);
	}
	public WebDataBinder(@Nullable Object target, String objectName) {
		super(target, objectName);
	}

	... //  省略get/set
	// 在父类的基础上，增加了对_和!的处理~~~
	@Override
	protected void doBind(MutablePropertyValues mpvs) {
		checkFieldDefaults(mpvs);
		checkFieldMarkers(mpvs);
		super.doBind(mpvs);
	}

	protected void checkFieldDefaults(MutablePropertyValues mpvs) {
		String fieldDefaultPrefix = getFieldDefaultPrefix();
		if (fieldDefaultPrefix != null) {
			PropertyValue[] pvArray = mpvs.getPropertyValues();
			for (PropertyValue pv : pvArray) {

				// 若你给定的PropertyValue的属性名确实是以!打头的  那就做处理如下：
				// 如果JavaBean的该属性可写 && mpvs不存在去掉!后的同名属性，那就添加进来表示后续可以使用了（毕竟是默认值，没有精确匹配的高的）
				// 然后把带!的给移除掉（因为默认值以已经转正了~~~）
				// 其实这里就是说你可以使用！来给个默认值。比如!name表示若找不到name这个属性的时，就取它的值~~~
				// 也就是说你request里若有穿!name保底，也就不怕出现null值啦~
				if (pv.getName().startsWith(fieldDefaultPrefix)) {
					String field = pv.getName().substring(fieldDefaultPrefix.length());
					if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) {
						mpvs.add(field, pv.getValue());
					}
					mpvs.removePropertyValue(pv);
				}
			}
		}
	}

	// 处理_的步骤
	// 若传入的字段以_打头
	// JavaBean的这个属性可写 && mpvs木有去掉_后的属性名字
	// getEmptyValue(field, fieldType)就是根据Type类型给定默认值。
	// 比如Boolean类型默认给false，数组给空数组[]，集合给空集合，Map给空map  可以参考此类：CollectionFactory
	// 当然，这一切都是建立在你传的属性值是以_打头的基础上的，Spring才会默认帮你处理这些默认值
	protected void checkFieldMarkers(MutablePropertyValues mpvs) {
		String fieldMarkerPrefix = getFieldMarkerPrefix();
		if (fieldMarkerPrefix != null) {
			PropertyValue[] pvArray = mpvs.getPropertyValues();
			for (PropertyValue pv : pvArray) {
				if (pv.getName().startsWith(fieldMarkerPrefix)) {
					String field = pv.getName().substring(fieldMarkerPrefix.length());
					if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) {
						Class<?> fieldType = getPropertyAccessor().getPropertyType(field);
						mpvs.add(field, getEmptyValue(field, fieldType));
					}
					mpvs.removePropertyValue(pv);
				}
			}
		}
	}

	// @since 5.0
	@Nullable
	public Object getEmptyValue(Class<?> fieldType) {
		try {
			if (boolean.class == fieldType || Boolean.class == fieldType) {
				// Special handling of boolean property.
				return Boolean.FALSE;
			} else if (fieldType.isArray()) {
				// Special handling of array property.
				return Array.newInstance(fieldType.getComponentType(), 0);
			} else if (Collection.class.isAssignableFrom(fieldType)) {
				return CollectionFactory.createCollection(fieldType, 0);
			} else if (Map.class.isAssignableFrom(fieldType)) {
				return CollectionFactory.createMap(fieldType, 0);
			}
		} catch (IllegalArgumentException ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Failed to create default value - falling back to null: " + ex.getMessage());
			}
		}
		// 若不在这几大类型内，就返回默认值null呗~~~
		// 但需要说明的是，若你是简单类型比如int，
		// Default value: null. 
		return null;
	}

	// 单独提供的方法，用于绑定org.springframework.web.multipart.MultipartFile类型的数据到JavaBean属性上~
	// 显然默认是允许MultipartFile作为Bean一个属性  参与绑定的
	// Map<String, List<MultipartFile>>它的key，一般来说就是文件们啦~
	protected void bindMultipart(Map<String, List<MultipartFile>> multipartFiles, MutablePropertyValues mpvs) {
		multipartFiles.forEach((key, values) -> {
			if (values.size() == 1) {
				MultipartFile value = values.get(0);
				if (isBindEmptyMultipartFiles() || !value.isEmpty()) {
					mpvs.add(key, value);
				}
			}
			else {
				mpvs.add(key, values);
			}
		});
	}
}

@Getter
@Setter
@ToString
public class Person {

    public String name;
    public Integer age;

    // 基本数据类型
    public Boolean flag;
    public int index;
    public List<String> list;
    public Map<String, String> map;

}

    public static void main(String[] args) {
        Person person = new Person();
        WebDataBinder binder = new WebDataBinder(person, "person");

        // 设置属性（此处演示一下默认值）
        MutablePropertyValues pvs = new MutablePropertyValues();

        // 使用!来模拟各个字段手动指定默认值
        //pvs.add("name", "fsx");
        pvs.add("!name", "不知火舞");
        pvs.add("age", 18);
        pvs.add("!age", 10); // 上面有确切的值了，默认值不会再生效

        binder.bind(pvs);
        System.out.println(person);
    }

Person(name=null, age=null, flag=false, index=0, list=[], map={})

public class ServletRequestDataBinder extends WebDataBinder {
	... // 沿用父类构造
	// 注意这个可不是父类的方法，是本类增强的~~~~意思就是kv都从request里来~~当然内部还是适配成了一个MutablePropertyValues
	public void bind(ServletRequest request) {
		// 内部最核心方法是它：WebUtils.getParametersStartingWith()  把request参数转换成一个Map
		// request.getParameterNames()
		MutablePropertyValues mpvs = new ServletRequestParameterPropertyValues(request);
		MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class);
	
		// 调用父类的bindMultipart方法，把MultipartFile都放进MutablePropertyValues里去~~~
		if (multipartRequest != null) {
			bindMultipart(multipartRequest.getMultiFileMap(), mpvs);
		}
		// 这个方法是本类流出来的一个扩展点~~~子类可以复写此方法自己往里继续添加
		// 比如ExtendedServletRequestDataBinder它就复写了这个方法，进行了增强（下面会说）  支持到了uriTemplateVariables的绑定
		addBindValues(mpvs, request);
		doBind(mpvs);
	}

	// 这个方法和父类的close方法类似，很少直接调用
	public void closeNoCatch() throws ServletRequestBindingException {
		if (getBindingResult().hasErrors()) {
			throw new ServletRequestBindingException("Errors binding onto object '" + getBindingResult().getObjectName() + "'", new BindException(getBindingResult()));
		}
	}
}

    public static void main(String[] args) {
        Person person = new Person();
        ServletRequestDataBinder binder = new ServletRequestDataBinder(person, "person");

        // 构造参数，此处就不用MutablePropertyValues，以HttpServletRequest的实现类MockHttpServletRequest为例吧
        MockHttpServletRequest request = new MockHttpServletRequest();
        // 模拟请求参数
        request.addParameter("name", "fsx");
        request.addParameter("age", "18");

        // flag不仅仅可以用true/false  用0和1也是可以的？
        request.addParameter("flag", "1");

        // 设置多值的
        request.addParameter("list", "4", "2", "3", "1");
        // 给map赋值(Json串)
        // request.addParameter("map", "{'key1':'value1','key2':'value2'}"); // 这样可不行
        request.addParameter("map['key1']", "value1");
        request.addParameter("map['key2']", "value2");

        //// 一次性设置多个值（传入Map）
        //request.setParameters(new HashMap<String, Object>() {{
        //    put("name", "fsx");
        //    put("age", "18");
        //}});

        binder.bind(request);
        System.out.println(person);
    }

Person(name=fsx, age=18, flag=true, index=0, list=[4, 2, 3, 1], map={key1=value1, key2=value2})

// @since 3.1
public class ExtendedServletRequestDataBinder extends ServletRequestDataBinder {
	... // 沿用父类构造

	//本类的唯一方法
	@Override
	@SuppressWarnings("unchecked")
	protected void addBindValues(MutablePropertyValues mpvs, ServletRequest request) {
		// 它的值是：HandlerMapping.class.getName() + ".uriTemplateVariables";
		String attr = HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE;

		// 注意：此处是attr，而不是parameter
		Map<String, String> uriVars = (Map<String, String>) request.getAttribute(attr);
		if (uriVars != null) {
			uriVars.forEach((name, value) -> {
				
				// 若已经存在确切的key了，不会覆盖~~~~
				if (mpvs.contains(name)) {
					if (logger.isWarnEnabled()) {
						logger.warn("Skipping URI variable '" + name + "' because request contains bind value with same name.");
					}
				} else {
					mpvs.addPropertyValue(name, value);
				}
			});
		}
	}
}

data binding from URL query params or form data in the request data to Java objects

public class PropertyEditorRegistrySupport implements PropertyEditorRegistry {

	@Nullable
	private Map<Class<?>, PropertyEditor> defaultEditors;

	private void createDefaultEditors() {
		this.defaultEditors = new HashMap<>(64);

		// Simple editors, without parameterization capabilities.
		// The JDK does not contain a default editor for any of these target types.
		this.defaultEditors.put(Charset.class, new CharsetEditor());
		this.defaultEditors.put(Class.class, new ClassEditor());
		...
		// Default instances of collection editors.
		// Can be overridden by registering custom instances of those as custom editors.
		this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class));
		this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class));
		this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class));
		this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class));
		this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class));
		...
		// 这里就部全部枚举出来了
	}
}

@Getter
@Setter
@ToString
public class Person {

    public String name;
    public Integer age;

    // 以Date类型为示例
    private Date start;
    private Date end;
    private Date endTest;

}

    public static void main(String[] args) {
        Person person = new Person();
        DataBinder binder = new DataBinder(person, "person");

        // 设置属性
        MutablePropertyValues pvs = new MutablePropertyValues();
        pvs.add("name", "fsx");

        // 事件类型绑定
        pvs.add("start", new Date());
        pvs.add("end", "2019-07-20");
        // 试用试用标准的事件日期字符串形式~
        pvs.add("endTest", "Sat Jul 20 11:00:22 CST 2019");


        binder.bind(pvs);
        System.out.println(person);
    }

Person(name=fsx, age=null, start=Sat Jul 20 11:05:29 CST 2019, end=null, endTest=Sun Jul 21 01:00:22 CST 2019)

@Getter
@Setter
@ToString
public class Person {
    private String name;
    // 备注：child是有有一个入参的构造器的
    private Child child;
}

@Getter
@Setter
@ToString
public class Child {
    private String name;
    private Integer age;
    public Child() {
    }
    public Child(String name) {
        this.name = name;
    }
}

    public static void main(String[] args) {
        Person person = new Person();
        DataBinder binder = new DataBinder(person, "person");

        // 设置属性
        MutablePropertyValues pvs = new MutablePropertyValues();
        pvs.add("name", "fsx");

        // 给child赋值，其实也可以传一个字符串就行了 非常的方便   Spring会自动给我们new对象
        pvs.add("child", "fsx-son");
        
        binder.bind(pvs);
        System.out.println(person);
    }

Person(name=fsx, child=Child(name=fsx-son, age=null))

public class MyDatePropertyEditor extends PropertyEditorSupport {

    private static final String PATTERN = "yyyy-MM-dd";

    @Override
    public String getAsText() {
        Date date = (Date) super.getValue();
        return new SimpleDateFormat(PATTERN).format(date);
    }

    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        try {
            super.setValue(new SimpleDateFormat(PATTERN).parse(text));
        } catch (ParseException e) {
            System.out.println("ParseException....................");
        }
    }
}

    public static void main(String[] args) {
        Person person = new Person();
        DataBinder binder = new DataBinder(person, "person");
        binder.registerCustomEditor(Date.class, new MyDatePropertyEditor());
        //binder.registerCustomEditor(Date.class, "end", new MyDatePropertyEditor());

        // 设置属性
        MutablePropertyValues pvs = new MutablePropertyValues();
        pvs.add("name", "fsx");

        // 事件类型绑定
        pvs.add("start", new Date());
        pvs.add("end", "2019-07-20");
        // 试用试用标准的事件日期字符串形式~
        pvs.add("endTest", "Sat Jul 20 11:00:22 CST 2019");


        binder.bind(pvs);
        System.out.println(person);
    }

ParseException....................
Person(name=fsx, age=null, start=Sat Jul 20 11:41:49 CST 2019, end=Sat Jul 20 00:00:00 CST 2019, endTest=null)

// @since 2.5   Spring在初始化WebDataBinder时候的回调接口，给调用者自定义~
public interface WebBindingInitializer {

	// @since 5.0
	void initBinder(WebDataBinder binder);

	// @deprecated as of 5.0 in favor of {@link #initBinder(WebDataBinder)}
	@Deprecated
	default void initBinder(WebDataBinder binder, WebRequest request) {
		initBinder(binder);
	}

}

public class ConfigurableWebBindingInitializer implements WebBindingInitializer {
	private boolean autoGrowNestedPaths = true;
	private boolean directFieldAccess = false; // 显然这里是false

	// 下面这些参数，不就是WebDataBinder那些可以配置的属性们吗？
	@Nullable
	private MessageCodesResolver messageCodesResolver;
	@Nullable
	private BindingErrorProcessor bindingErrorProcessor;
	@Nullable
	private Validator validator;
	@Nullable
	private ConversionService conversionService;
	// 此处使用的PropertyEditorRegistrar来管理的，最终都会被注册进PropertyEditorRegistry嘛
	@Nullable
	private PropertyEditorRegistrar[] propertyEditorRegistrars;

	... //  省略所有get/set
	
	// 它做的事无非就是把配置的值都放进去而已~~
	@Override
	public void initBinder(WebDataBinder binder) {
		binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
		if (this.directFieldAccess) {
			binder.initDirectFieldAccess();
		}
		if (this.messageCodesResolver != null) {
			binder.setMessageCodesResolver(this.messageCodesResolver);
		}
		if (this.bindingErrorProcessor != null) {
			binder.setBindingErrorProcessor(this.bindingErrorProcessor);
		}
		// 可以看到对校验器这块  内部还是做了容错的
		if (this.validator != null && binder.getTarget() != null && this.validator.supports(binder.getTarget().getClass())) {
			binder.setValidator(this.validator);
		}
		if (this.conversionService != null) {
			binder.setConversionService(this.conversionService);
		}
		if (this.propertyEditorRegistrars != null) {
			for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
				propertyEditorRegistrar.registerCustomEditors(binder);
			}
		}
	}
}

// @since 3.1   注意：WebDataBinder 可是1.2就有了~
public interface WebDataBinderFactory {
	// 此处使用的是Spring自己的NativeWebRequest   后面两个参数就不解释了
	WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception;
}

public class DefaultDataBinderFactory implements WebDataBinderFactory {
	@Nullable
	private final WebBindingInitializer initializer;
	// 注意：这是唯一构造函数
	public DefaultDataBinderFactory(@Nullable WebBindingInitializer initializer) {
		this.initializer = initializer;
	}

	// 实现接口的方法
	@Override
	@SuppressWarnings("deprecation")
	public final WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception {

		WebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);
		
		// 可见WebDataBinder 创建好后，此处就会回调（只有一个）
		if (this.initializer != null) {
			this.initializer.initBinder(dataBinder, webRequest);
		}
		// 空方法 子类去实现，比如InitBinderDataBinderFactory实现了词方法
		initBinder(dataBinder, webRequest);
		return dataBinder;
	}

	//  子类可以复写，默认实现是WebRequestDataBinder
	// 比如子类ServletRequestDataBinderFactory就复写了，使用的new ExtendedServletRequestDataBinder(target, objectName)
	protected WebDataBinder createBinderInstance(@Nullable Object target, String objectName, NativeWebRequest webRequest) throws Exception 
		return new WebRequestDataBinder(target, objectName);
	}
}

// @since 3.1
public class InitBinderDataBinderFactory extends DefaultDataBinderFactory {
	
	// 需要注意的是：`@InitBinder`可以标注N多个方法~  所以此处是List
	private final List<InvocableHandlerMethod> binderMethods;

	// 此子类的唯一构造函数
	public InitBinderDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods, @Nullable WebBindingInitializer initializer) {
		super(initializer);
		this.binderMethods = (binderMethods != null ? binderMethods : Collections.emptyList());
	}

	// 上面知道此方法的调用方法生initializer.initBinder之后
	// 所以使用注解它生效的时机是在直接实现接口的后面的~
	@Override
	public void initBinder(WebDataBinder dataBinder, NativeWebRequest request) throws Exception {
		for (InvocableHandlerMethod binderMethod : this.binderMethods) {
			// 判断@InitBinder是否对dataBinder持有的target对象生效~~~（根据name来匹配的）
			if (isBinderMethodApplicable(binderMethod, dataBinder)) {
				// 关于目标方法执行这块，可以参考另外一篇@InitBinder的原理说明~
				Object returnValue = binderMethod.invokeForRequest(request, null, dataBinder);

				// 标注@InitBinder的方法不能有返回值
				if (returnValue != null) {
					throw new IllegalStateException("@InitBinder methods must not return a value (should be void): " + binderMethod);
				}
			}
		}
	}

	//@InitBinder有个Value值，它是个数组。它是用来匹配dataBinder.getObjectName()是否匹配的   若匹配上了，现在此注解方法就会生效
	// 若value为空，那就对所有生效~~~
	protected boolean isBinderMethodApplicable(HandlerMethod initBinderMethod, WebDataBinder dataBinder) {
		InitBinder ann = initBinderMethod.getMethodAnnotation(InitBinder.class);
		Assert.state(ann != null, "No InitBinder annotation");
		String[] names = ann.value();
		return (ObjectUtils.isEmpty(names) || ObjectUtils.containsElement(names, dataBinder.getObjectName()));
	}
}

// @since 3.1
public class ServletRequestDataBinderFactory extends InitBinderDataBinderFactory {
	public ServletRequestDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods, @Nullable WebBindingInitializer initializer) {
		super(binderMethods, initializer);
	}
	@Override
	protected ServletRequestDataBinder createBinderInstance(
			@Nullable Object target, String objectName, NativeWebRequest request) throws Exception  {
		return new ExtendedServletRequestDataBinder(target, objectName);
	}
}