springmvc--7--数据绑定器WebDataBinder

深藏阁楼爱情的钟 2022-11-01 14:58 663阅读 0赞

# springmvc–数据绑定器`WebDataBinder` #

### 文章目录 ###

*  springmvc--数据绑定器\`WebDataBinder\`
 *  1 简单介绍
 *  2 \`ServletRequestDataBinderFactory\`
 *   *  2.1 构造方法
     *  2.2 \`createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName)\`方法，创建属性对应的数据绑定器
     *   *  2.2.1 创建数据绑定器实例
         *  2.2.2 初始化数据绑定器
 *  3 \`ConfigurableWebBindingInitializer\`
 *   *  3.1 \`initBinder(WebDataBinder binder)\`方法，初始化属性绑定器
 *  4 \`ExtendedServletRequestDataBinder\`
 *   *  4.1 构造方法
     *  4.2 \`DataBinder\`的字段
     *   *  4.2.1 \`setAutoGrowNestedPaths(boolean autoGrowNestedPaths)\`方法，设置是否处理嵌套属性
         *  4.2.2 \`getObjectName()\`方法，获取要绑定参数的参数名
         *  4.2.3 \`getTarget()\`方法，获取要绑定的对象
         *  4.2.4 \`getValidators()\`方法， 获取配置的所有的校验器
         *  4.2.5 \`getBindingResult()\`方法，获取\`BindingResult\`绑定结果
     *  4.3 \`validate(Object... validationHints)\`方法，校验数据
     *  4.4 \`initBeanPropertyAccess()\`方法，初始化\`bean属性寄存器\`
     *  4.5 \`bind(ServletRequest request)\`方法，数据绑定器的核心方法之一
     *   *  4.5.1 将文件上传映射添加到\`MutablePropertyValues\`中
         *  4.5.2 将模板变量映射添加到\`MutablePropertyValues\`中
         *  4.5.3 绑定到\`javaBean\`对象中
         *   *  4.5.3.1 检查所有默认字段，去掉那些不可写的字段
             *  4.5.3.2 检查所有字段标记，去掉那些不可写的字段
             *  4.5.3.3 检查所有字段，移除掉用户指定的不允许绑定的字段
             *  4.5.3.4 检查用户指定的必须绑定的字段有没有对应值
             *  4.5.3.5 进行对象属性填充
         *  4.6 \`getPropertyAccessor()\`方法，获取需要绑定对象的属性寄存器
 *  5 \`BeanPropertyBindingResult\`
 *   *  5.1 它们拥有的字段
     *   *  5.1.1 \`hasErrors()\`方法，判断数据绑定过程中是否产生错误
     *  5.2 构造方法
     *  5.3 \`getModel()\`方法，获取绑定结果的模型数据
 *  6 \`ServletRequestParameterPropertyValues\`

# 1 简单介绍 #

数据绑定不是`springmvc`所特有的，早在`spring`的时候就已经存在了，当时是`DataBinder`，后来`springmvc`在其基础上扩展，并广泛应用。数据绑定器可以完成如下功能

*  类型转换
 *  数据校验
 *  属性填充

接下来我们就来看一下它是如何完成这三大功能的

# 2 `ServletRequestDataBinderFactory` #

类图如下

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center]

> 它的顶层接口是`WebDataBinderFactory`，我们先看一下这个接口

public interface WebDataBinderFactory { 
    
        /** * Create a {@link WebDataBinder} for the given object. * @param webRequest the current request * @param target the object to create a data binder for, * or {@code null} if creating a binder for a simple type * @param objectName the name of the target object * @return the created {@link WebDataBinder} instance, never null * @throws Exception raised if the creation and initialization of the data binder fails */
        WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName)
            throws Exception;
    
    }

> 只有一个方法，用来创建一个`WebDataBinder`数据绑定器对象

## 2.1 构造方法 ##

/** * initializer默认为ConfigurableWebBindingInitializer * springmvc配置文件中使用`<mvc:annotation-driven>`，会通过属性填充给它一个默认值 */
 public ServletRequestDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods,
 @Nullable WebBindingInitializer initializer) { 
 
 super(binderMethods, initializer);
 }

父类`InitBinderDataBinderFactory`构造方法

//保存有@InitBinder注解的方法
 private final List<InvocableHandlerMethod> binderMethods;
 
 /** * Create a new InitBinderDataBinderFactory instance. * @param binderMethods {@code @InitBinder} methods * @param initializer for global data binder initialization */
 public InitBinderDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods,
 @Nullable WebBindingInitializer initializer) { 
 
 super(initializer);
 this.binderMethods = (binderMethods != null ? binderMethods : Collections.emptyList());
 }

父类`DefaultDataBinderFactory`构造方法

/** * 绑定器的初始化器 * 使用这个初始化器来初始化绑定器 */
    @Nullable
    private final WebBindingInitializer initializer;
    
    
    /** * Create a new {@code DefaultDataBinderFactory} instance. * @param initializer for global data binder initialization * (or {@code null} if none) */
    public DefaultDataBinderFactory(@Nullable WebBindingInitializer initializer) { 
       this.initializer = initializer;
    }

> 构造方法只是简单的将两个参数对象赋值给属性

## 2.2 `createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName)`方法，创建属性对应的数据绑定器 ##

/** * Create a new {@link WebDataBinder} for the given target object and * initialize it through a {@link WebBindingInitializer}. * @throws Exception in case of invalid state or arguments */
    @Override
    @SuppressWarnings("deprecation")
    public final WebDataBinder createBinder(
        NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception { 
    
        //创建数据绑定器实例，见2.2.1
        WebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);
        //初始化器初始化数据绑定器，见3.1
        if (this.initializer != null) { 
            this.initializer.initBinder(dataBinder, webRequest);
        }
        //初始化数据绑定器，见2.2.2
        initBinder(dataBinder, webRequest);
        return dataBinder;
    }

### 2.2.1 创建数据绑定器实例 ###

/** * Returns an instance of {@link ExtendedServletRequestDataBinder}. */
    @Override
    protected ServletRequestDataBinder createBinderInstance(
        @Nullable Object target, String objectName, NativeWebRequest request) throws Exception  { 
    
        /** * 创建一个数据绑定器，见4.1 * 实际类型是ExtendedServletRequestDataBinder */
        return new ExtendedServletRequestDataBinder(target, objectName);
    }

### 2.2.2 初始化数据绑定器 ###

/** * Initialize a WebDataBinder with {@code @InitBinder} methods. * If the {@code @InitBinder} annotation specifies attributes names, * it is invoked only if the names include the target object name. * @throws Exception if one of the invoked @{@link InitBinder} methods fails * @see #isBinderMethodApplicable */
 @Override
 public void initBinder(WebDataBinder dataBinder, NativeWebRequest request) throws Exception { 
 //遍历所有的@InitBinder注解的方法
 for (InvocableHandlerMethod binderMethod : this.binderMethods) { 
 //过滤掉不符合条件的方法
 if (isBinderMethodApplicable(binderMethod, dataBinder)) { 
 /** * 反射执行@InitBinder注解的方法 * 方法源码内容在springmvc--7--ServletInvocableHandlerMethod增强的处理器方法 */
 Object returnValue = binderMethod.invokeForRequest(request, null, dataBinder);
 if (returnValue != null) { 
 throw new IllegalStateException(
 "@InitBinder methods must not return a value (should be void): " + binderMethod);
 }
 }
 }
 }

过滤掉不符合条件的方法

/** * Determine whether the given {@code @InitBinder} method should be used * to initialize the given {@link WebDataBinder} instance. By default we * check the specified attribute names in the annotation value, if any. */
    protected boolean isBinderMethodApplicable(HandlerMethod initBinderMethod, WebDataBinder dataBinder) { 
        //获取方法上@InitBinder注解信息
        InitBinder ann = initBinderMethod.getMethodAnnotation(InitBinder.class);
        Assert.state(ann != null, "No InitBinder annotation");
        String[] names = ann.value();
        /** * 如果注解未指定value属性值，则表示所有的绑定器都要执行该方法进行初始化 * 如果指定了，那么就会判断要绑定参数的参数名，只有和注解上指定的匹配，才会执行 * 该注解方法进行初始化 * getObjectName()方法，获取要绑定参数的参数名，见4.2.2 */
        return (ObjectUtils.isEmpty(names) || ObjectUtils.containsElement(names, dataBinder.getObjectName()));
    }

> 遍历所有标注`@InitBinder`注解的方法，逐个过滤，判定通过之后才会执行方法
> 
>  *  如果注解未指定`value`属性值，判定通过
>  *  如果注解指定了`value`属性值，那么就判断要绑定参数的参数名，只有和注解上指定的匹配，才会判定通过

# 3 `ConfigurableWebBindingInitializer` #

> 这是`springmvc`默认的初始化器，它继承了`WebBindingInitializer`接口

public interface WebBindingInitializer { 
    
        /** * 初始化数据绑定器，5.0以后使用这个方法 * @since 5.0 */
        void initBinder(WebDataBinder binder);
    
        /** * 该方法已经被废弃了，但是在springmvc5.2中还未修改过来，于是 * 通过默认实现回调5.0新增的接口方法 */
        @Deprecated
        default void initBinder(WebDataBinder binder, WebRequest request) { 
            initBinder(binder);
        }
    }

我们来看看`ConfigurableWebBindingInitializer`类的属性

public class ConfigurableWebBindingInitializer implements WebBindingInitializer { 
    
        //是否开启处理嵌套属性
        private boolean autoGrowNestedPaths = true;
    
        private boolean directFieldAccess = false;
    
        @Nullable
        private MessageCodesResolver messageCodesResolver;
    
        @Nullable
        private BindingErrorProcessor bindingErrorProcessor;
    
        //数据校验器
        @Nullable
        private Validator validator;
    
        //统一转换服务
        @Nullable
        private ConversionService conversionService;
    
        //属性注册器注册商
        @Nullable
        private PropertyEditorRegistrar[] propertyEditorRegistrars;
    }

## 3.1 `initBinder(WebDataBinder binder)`方法，初始化属性绑定器 ##

/** * Initialize the given DataBinder for the given (Servlet) request. * @param binder the DataBinder to initialize * @param request the web request that the data binding happens within * @deprecated as of 5.0 in favor of {@link #initBinder(WebDataBinder)} */
    @Deprecated
    default void initBinder(WebDataBinder binder, WebRequest request) { 
        initBinder(binder);
    }

> 上面这个方法在`5.0`之后就被废弃掉了，该方法里面回调了`initBinder(binder)`方法，源码如下所示

@Override
    public void initBinder(WebDataBinder binder) { 
        //设置处理嵌套属性,见4.2.1
        binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
        
        /** * 直接通过字段绑定属性，而不是setter方法，见4.4 */
        if (this.directFieldAccess) { 
            binder.initDirectFieldAccess();
        }
        //消息码解析器
        if (this.messageCodesResolver != null) { 
            binder.setMessageCodesResolver(this.messageCodesResolver);
        }
        //绑定错误处理器
        if (this.bindingErrorProcessor != null) { 
            binder.setBindingErrorProcessor(this.bindingErrorProcessor);
        }
        //数据校验器
        if (this.validator != null && binder.getTarget() != null &&
            this.validator.supports(binder.getTarget().getClass())) { 
            binder.setValidator(this.validator);
        }
        //统一转换服务
        if (this.conversionService != null) { 
            binder.setConversionService(this.conversionService);
        }
        //属性编辑器注册器商，批量注册属性编辑器到数据绑定器中
        if (this.propertyEditorRegistrars != null) { 
            for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) { 
                propertyEditorRegistrar.registerCustomEditors(binder);
            }
        }
    }

> 实际上就是将用户在初始化器上的配置覆盖到数据绑定器中

# 4 `ExtendedServletRequestDataBinder` #

> 这是`springmvc`默认使用的数据绑定器`DataBinder`，见`2.2.1`

它的类图如下所示

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 1]

> 在学习`spring`的类型转换时，我们就接触过了`TypeConverter`接口和`PropertyEditorRegistry`接口，我们熟知的`BeanWrapperImpl`也实现了这两个接口
> 
>  *  `TypeConverter`接口：`spring`属性填充阶段，调用该接口的`convertForProperty(value, propertyName)`方法完成该属性的类型转换
>  *  `PropertyEditorRegistry`接口：`PropertyEditor`注册中心，提供注册和查找指定转换类型的`PropertyEditor`方法

下面是`ExtendedServletRequestDataBinder`和`BeanWrapperImpl`的结构比较

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 2]

## 4.1 构造方法 ##

/** * Create a new instance. * @param target the target object to bind onto (or {@code null} * if the binder is just used to convert a plain parameter value) * @param objectName the name of the target object * @see #DEFAULT_OBJECT_NAME */
    public ExtendedServletRequestDataBinder(@Nullable Object target, String objectName) { 
       super(target, objectName);
    }

父类`ServletRequestDataBinder`的构造方法

/** * Create a new ServletRequestDataBinder instance. * @param target the target object to bind onto (or {@code null} * if the binder is just used to convert a plain parameter value) * @param objectName the name of the target object */
    public ServletRequestDataBinder(@Nullable Object target, String objectName) { 
       super(target, objectName);
    }

父类`WebDataBinder`的构造方法

/** * Create a new WebDataBinder instance. * @param target the target object to bind onto (or {@code null} * if the binder is just used to convert a plain parameter value) * @param objectName the name of the target object */
    public WebDataBinder(@Nullable Object target, String objectName) { 
       super(target, objectName);
    }

父类`DataBinder`的构造方法

//要绑定的对象
    @Nullable
    private final Object target;
    
    //要绑定参数的参数名
    private final String objectName;
    
    
    /** * Create a new DataBinder instance. * @param target the target object to bind onto (or {@code null} * if the binder is just used to convert a plain parameter value) * @param objectName the name of the target object */
    public DataBinder(@Nullable Object target, String objectName) { 
        //从Optional容器中取出原始对象
        this.target = ObjectUtils.unwrapOptional(target);
        this.objectName = objectName;
    }

> 构造方法额外做什么事情，只是简单的将两个参数值保存到字段中

## 4.2 `DataBinder`的字段 ##

public class DataBinder implements PropertyEditorRegistry, TypeConverter { 
 
 /** Default object name used for binding: "target". */
 public static final String DEFAULT_OBJECT_NAME = "target";
 
 /** Default limit for array and collection growing: 256. */
 public static final int DEFAULT_AUTO_GROW_COLLECTION_LIMIT = 256;
 
 //要绑定的对象
 @Nullable
 private final Object target;
 
 //要绑定参数的参数名
 private final String objectName;
 
 //绑定结果
 @Nullable
 private AbstractPropertyBindingResult bindingResult;
 
 @Nullable
 private SimpleTypeConverter typeConverter;
 
 private boolean ignoreUnknownFields = true;
 
 private boolean ignoreInvalidFields = false;
 
 //是否处理嵌套属性
 private boolean autoGrowNestedPaths = true;
 
 private int autoGrowCollectionLimit = DEFAULT_AUTO_GROW_COLLECTION_LIMIT;
 
 @Nullable
 private String[] allowedFields;
 
 @Nullable
 private String[] disallowedFields;
 
 @Nullable
 private String[] requiredFields;
 
 //统一转换服务
 @Nullable
 private ConversionService conversionService;
 
 @Nullable
 private MessageCodesResolver messageCodesResolver;
 
 private BindingErrorProcessor bindingErrorProcessor = new DefaultBindingErrorProcessor();
 
 //校验器，默认是空的，需要用户自己配置
 private final List<Validator> validators = new ArrayList<>();
 }

> 上面字段的`setter`或`getter`方法统一放在这个章节下面

### 4.2.1 `setAutoGrowNestedPaths(boolean autoGrowNestedPaths)`方法，设置是否处理嵌套属性 ###

public void setAutoGrowNestedPaths(boolean autoGrowNestedPaths) { 
        Assert.state(this.bindingResult == null,
                     "DataBinder is already initialized - call setAutoGrowNestedPaths before other configuration methods");
        this.autoGrowNestedPaths = autoGrowNestedPaths;
    }

### 4.2.2 `getObjectName()`方法，获取要绑定参数的参数名 ###

public String getObjectName() { 
       return this.objectName;
    }

### 4.2.3 `getTarget()`方法，获取要绑定的对象 ###

@Nullable
    public Object getTarget() { 
       return this.target;
    }

### 4.2.4 `getValidators()`方法， 获取配置的所有的校验器 ###

public List<Validator> getValidators() { 
 return Collections.unmodifiableList(this.validators);
 }

### 4.2.5 `getBindingResult()`方法，获取`BindingResult`绑定结果 ###

public BindingResult getBindingResult() { 
        //获取BindingResult
        return getInternalBindingResult();
    }

获取`BindingResult`

/** * Return the internal BindingResult held by this DataBinder, * as an AbstractPropertyBindingResult. */
    protected AbstractPropertyBindingResult getInternalBindingResult() { 
        //没有就创建一个，有就直接返回
        if (this.bindingResult == null) { 
            //初始化bean属性寄存器，见4.4
            initBeanPropertyAccess();
        }
        return this.bindingResult;
    }

## 4.3 `validate(Object... validationHints)`方法，校验数据 ##

/** * Invoke the specified Validators, if any, with the given validation hints. * Note: Validation hints may get ignored by the actual target Validator. * @param validationHints one or more hint objects to be passed to a {@link SmartValidator} * @since 3.1 * @see #setValidator(Validator) * @see SmartValidator#validate(Object, Errors, Object...) */
 public void validate(Object... validationHints) { 
 //得到要绑定的对象，见4.2.3
 Object target = getTarget();
 Assert.state(target != null, "No target to validate");
 //获取绑定结果
 BindingResult bindingResult = getBindingResult();
 // Call each validator with the same binding result
 /** * 遍历所有的校验器，校验数据 * getValidators()方法，获取配置的所有的校验器，见4.2.4 */
 for (Validator validator : getValidators()) { 
 if (!ObjectUtils.isEmpty(validationHints) && validator instanceof SmartValidator) { 
 ((SmartValidator) validator).validate(target, bindingResult, validationHints);
 }
 else if (validator != null) { 
 validator.validate(target, bindingResult);
 }
 }
 }

## 4.4 `initBeanPropertyAccess()`方法，初始化`bean属性寄存器` ##

/** * Initialize standard JavaBean property access for this DataBinder. * This is the default; an explicit call just leads to eager initialization. * @see #initDirectFieldAccess() * @see #createBeanPropertyBindingResult() */
 public void initBeanPropertyAccess() { 
 Assert.state(this.bindingResult == null,
 "DataBinder is already initialized - call initBeanPropertyAccess before other configuration methods");
 //创建一个BindingResult
 this.bindingResult = createBeanPropertyBindingResult();
 }

创建一个`BindingResult`

/** * Create the {@link AbstractPropertyBindingResult} instance using standard * JavaBean property access. * @since 4.2.1 */
    protected AbstractPropertyBindingResult createBeanPropertyBindingResult() { 
        //创建一个BeanPropertyBindingResult
        BeanPropertyBindingResult result = new BeanPropertyBindingResult(getTarget(),
                                                                         getObjectName(), isAutoGrowNestedPaths(), getAutoGrowCollectionLimit());
    
        //设置统一转换服务
        if (this.conversionService != null) { 
            result.initConversion(this.conversionService);
        }
        //设置消息码解析器
        if (this.messageCodesResolver != null) { 
            result.setMessageCodesResolver(this.messageCodesResolver);
        }
    
        return result;
    }

> `BeanPropertyBindingResult`：通过`setter`方法完成属性绑定

## 4.5 `bind(ServletRequest request)`方法，数据绑定器的核心方法之一 ##

> 该方法会将`request`请求参数绑定到`javaBean`对象中

/** * Bind the parameters of the given request to this binder's target, * also binding multipart files in case of a multipart request. * This call can create field errors, representing basic binding * errors like a required field (code "required"), or type mismatch * between value and bean property (code "typeMismatch"). * Multipart files are bound via their parameter name, just like normal * HTTP parameters: i.e. "uploadedFile" to an "uploadedFile" bean property, * invoking a "setUploadedFile" setter method. * The type of the target property for a multipart file can be MultipartFile, * byte[], or String. The latter two receive the contents of the uploaded file; * all metadata like original file name, content type, etc are lost in those cases. * @param request the request with parameters to bind (can be multipart) * @see org.springframework.web.multipart.MultipartHttpServletRequest * @see org.springframework.web.multipart.MultipartFile * @see #bind(org.springframework.beans.PropertyValues) */
 public void bind(ServletRequest request) { 
 /** * ServletRequestParameterPropertyValues中封装了所有请求参数,无前缀 */
 MutablePropertyValues mpvs = new ServletRequestParameterPropertyValues(request);
 //得到文件上传请求对象
 MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class);
 //文件上传请求的MultipartFile添加到mpvs中，见4.5.1
 if (multipartRequest != null) { 
 bindMultipart(multipartRequest.getMultiFileMap(), mpvs);
 }
 //将模板变量映射添加到mpvs中，见4.5.2
 addBindValues(mpvs, request);
 //绑定
 doBind(mpvs);
 }

### 4.5.1 将文件上传映射添加到`MutablePropertyValues`中 ###

/** * Bind all multipart files contained in the given request, if any * (in case of a multipart request). To be called by subclasses. * Multipart files will only be added to the property values if they * are not empty or if we're configured to bind empty multipart files too. * @param multipartFiles a Map of field name String to MultipartFile object * @param mpvs the property values to be bound (can be modified) * @see org.springframework.web.multipart.MultipartFile * @see #setBindEmptyMultipartFiles */
 protected void bindMultipart(Map<String, List<MultipartFile>> multipartFiles, MutablePropertyValues mpvs) { 
 //遍历，保存
 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);
 }
 });
 }

### 4.5.2 将模板变量映射添加到`MutablePropertyValues`中 ###

/** * Merge URI variables into the property values to use for data binding. */
 @Override
 @SuppressWarnings("unchecked")
 protected void addBindValues(MutablePropertyValues mpvs, ServletRequest request) { 
 /** * HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE= * org.springframework.web.servlet.HandlerMapping.uriTemplateVariables * 所有的模板变量映射都保存在这个请求域中 */
 String attr = HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE;
 Map<String, String> uriVars = (Map<String, String>) request.getAttribute(attr);
 if (uriVars != null) { 
 //遍历保存不重复的
 uriVars.forEach((name, value) -> { 
 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);
 }
 });
 }
 }

### 4.5.3 绑定到`javaBean`对象中 ###

/** * This implementation performs a field default and marker check * before delegating to the superclass binding process. * @see #checkFieldDefaults * @see #checkFieldMarkers */
    @Override
    protected void doBind(MutablePropertyValues mpvs) { 
        //检查所有默认字段，去掉那些不可写的字段,见4.5.3.1
        checkFieldDefaults(mpvs);
        //检查所有字段标记，去掉那些不可写的字段，见4.5.3.2
        checkFieldMarkers(mpvs);
        //父类再进一步处理，完成属性填充
        super.doBind(mpvs);
    }

父类`doBind(mpvs)`方法再进一步处理，完成属性填充

/** * Actual implementation of the binding process, working with the * passed-in MutablePropertyValues instance. * @param mpvs the property values to bind, * as MutablePropertyValues instance * @see #checkAllowedFields * @see #checkRequiredFields * @see #applyPropertyValues */
    protected void doBind(MutablePropertyValues mpvs) { 
        //检查所有字段，移除掉用户指定的不允许绑定的字段，见4.5.3.3
        checkAllowedFields(mpvs);
        //检查用户指定的必须绑定的字段有没有对应值，见4.5.3.4
        checkRequiredFields(mpvs);
        //进行对象属性填充
        applyPropertyValues(mpvs);
    }

#### 4.5.3.1 检查所有默认字段，去掉那些不可写的字段 ####

/** * Check the given property values for field defaults, * i.e. for fields that start with the field default prefix. * The existence of a field defaults indicates that the specified * value should be used if the field is otherwise not present. * @param mpvs the property values to be bound (can be modified) * @see #getFieldDefaultPrefix */
 protected void checkFieldDefaults(MutablePropertyValues mpvs) { 
 //fieldDefaultPrefix = "!"
 String fieldDefaultPrefix = getFieldDefaultPrefix();
 if (fieldDefaultPrefix != null) { 
 PropertyValue[] pvArray = mpvs.getPropertyValues();
 for (PropertyValue pv : pvArray) { 
 //以"!"开头，就截取下来，然后判断对应字段是否可写
 if (pv.getName().startsWith(fieldDefaultPrefix)) { 
 String field = pv.getName().substring(fieldDefaultPrefix.length());
 /** * getPropertyAccessor()方法， 获取需要绑定对象的属性寄存器 * isWritableProperty(field)方法，判断field对应的字段有没有setter方法 */
 if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) { 
 //保存
 mpvs.add(field, pv.getValue());
 }
 mpvs.removePropertyValue(pv);
 }
 }
 }
 }

> 对于以`!`开头的属性，截取掉`!`得到`field`，然后判`field`对应的字段是否可写，可写，就再次保存`field`映射关系到`MutablePropertyValues`中，并移除掉这个属性，否则直接移除掉这个属性

#### 4.5.3.2 检查所有字段标记，去掉那些不可写的字段 ####

/** * Check the given property values for field markers, * i.e. for fields that start with the field marker prefix. * The existence of a field marker indicates that the specified * field existed in the form. If the property values do not contain * a corresponding field value, the field will be considered as empty * and will be reset appropriately. * @param mpvs the property values to be bound (can be modified) * @see #getFieldMarkerPrefix * @see #getEmptyValue(String, Class) */
 protected void checkFieldMarkers(MutablePropertyValues mpvs) { 
 //fieldMarkerPrefix = "_"
 String fieldMarkerPrefix = getFieldMarkerPrefix();
 if (fieldMarkerPrefix != null) { 
 PropertyValue[] pvArray = mpvs.getPropertyValues();
 for (PropertyValue pv : pvArray) { 
 //以"_"开头，就截取下来，然后判断对应字段是否可写
 if (pv.getName().startsWith(fieldMarkerPrefix)) { 
 String field = pv.getName().substring(fieldMarkerPrefix.length());
 /** * getPropertyAccessor()方法， 获取需要绑定对象的属性寄存器 * isWritableProperty(field)方法，判断field对应的字段有没有setter方法 */
 if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) { 
 Class<?> fieldType = getPropertyAccessor().getPropertyType(field);
 mpvs.add(field, getEmptyValue(field, fieldType));
 }
 mpvs.removePropertyValue(pv);
 }
 }
 }
 }

> 对于以`_`开头的属性，截取掉`_`得到`field`，然后判`field`对应的字段是否可写，可写，就再次保存`field`映射关系到`MutablePropertyValues`中，并移除掉这个属性，否则直接移除掉这个属性

#### 4.5.3.3 检查所有字段，移除掉用户指定的不允许绑定的字段 ####

/** * Check the given property values against the allowed fields, * removing values for fields that are not allowed. * @param mpvs the property values to be bound (can be modified) * @see #getAllowedFields * @see #isAllowed(String) */
 protected void checkAllowedFields(MutablePropertyValues mpvs) { 
 PropertyValue[] pvs = mpvs.getPropertyValues();
 for (PropertyValue pv : pvs) { 
 String field = PropertyAccessorUtils.canonicalPropertyName(pv.getName());
 //移除所有不允许绑定的字段的映射
 if (!isAllowed(field)) { 
 mpvs.removePropertyValue(pv);
 getBindingResult().recordSuppressedField(field);
 if (logger.isDebugEnabled()) { 
 logger.debug("Field [" + field + "] has been removed from PropertyValues " +
 "and will not be bound, because it has not been found in the list of allowed fields");
 }
 }
 }
 }
 
 
 /** * Return if the given field is allowed for binding. * Invoked for each passed-in property value. * The default implementation checks for "xxx*", "*xxx" and "*xxx*" matches, * as well as direct equality, in the specified lists of allowed fields and * disallowed fields. A field matching a disallowed pattern will not be accepted * even if it also happens to match a pattern in the allowed list. * Can be overridden in subclasses. * @param field the field to check * @return if the field is allowed * @see #setAllowedFields * @see #setDisallowedFields * @see org.springframework.util.PatternMatchUtils#simpleMatch(String, String) */
 protected boolean isAllowed(String field) { 
 /** * 用户可以在数据绑定器中指定 * 允许绑定的字段allowedFields * 不允许绑定的字段disallowedFields */
 String[] allowed = getAllowedFields();
 String[] disallowed = getDisallowedFields();
 return ((ObjectUtils.isEmpty(allowed) || PatternMatchUtils.simpleMatch(allowed, field)) &&
 (ObjectUtils.isEmpty(disallowed) || !PatternMatchUtils.simpleMatch(disallowed, field)));
 }

> 该方法移除掉用户指定的不允许绑定的字段映射

#### 4.5.3.4 检查用户指定的必须绑定的字段有没有对应值 ####

/** * Check the given property values against the required fields, * generating missing field errors where appropriate. * @param mpvs the property values to be bound (can be modified) * @see #getRequiredFields * @see #getBindingErrorProcessor * @see BindingErrorProcessor#processMissingFieldError */
 protected void checkRequiredFields(MutablePropertyValues mpvs) { 
 /** * requiredFields字段保存所有必须绑定的字段名 * 用户可通过指定这些字段值来定制要绑定的字段 */
 String[] requiredFields = getRequiredFields();
 if (!ObjectUtils.isEmpty(requiredFields)) { 
 Map<String, PropertyValue> propertyValues = new HashMap<>();
 PropertyValue[] pvs = mpvs.getPropertyValues();
 for (PropertyValue pv : pvs) { 
 //规范名
 String canonicalName = PropertyAccessorUtils.canonicalPropertyName(pv.getName());
 propertyValues.put(canonicalName, pv);
 }
 //遍历所有必须填充字段
 for (String field : requiredFields) { 
 PropertyValue pv = propertyValues.get(field);
 boolean empty = (pv == null || pv.getValue() == null);
 if (!empty) { 
 //String
 if (pv.getValue() instanceof String) { 
 empty = !StringUtils.hasText((String) pv.getValue());
 }
 //String[]
 else if (pv.getValue() instanceof String[]) { 
 String[] values = (String[]) pv.getValue();
 empty = (values.length == 0 || !StringUtils.hasText(values[0]));
 }
 }
 //生成一个绑定错误并设置到绑定结果中
 if (empty) { 
 // Use bind error processor to create FieldError.
 getBindingErrorProcessor().processMissingFieldError(field, getInternalBindingResult());
 // Remove property from property values to bind:
 // It has already caused a field error with a rejected value.
 if (pv != null) { 
 mpvs.removePropertyValue(pv);
 propertyValues.remove(field);
 }
 }
 }
 }
 }

> `requiredFields`字段保存着所有必须绑定的字段名
> 
> 该方法遍历这些字段名，通过字段名从映射中取值，取不到值就生成一个绑定错误并设置到绑定结果中

#### 4.5.3.5 进行对象属性填充 ####

/** * Apply given property values to the target object. * Default implementation applies all of the supplied property * values as bean property values. By default, unknown fields will * be ignored. * @param mpvs the property values to be bound (can be modified) * @see #getTarget * @see #getPropertyAccessor * @see #isIgnoreUnknownFields * @see #getBindingErrorProcessor * @see BindingErrorProcessor#processPropertyAccessException */
 protected void applyPropertyValues(MutablePropertyValues mpvs) { 
 try { 
 // Bind request parameters onto target object.
 /** * getPropertyAccessor()方法， 获取javaBean对象的属性寄存器，即BeanWrapperImpl * setPropertyValues()方法，我们应该很熟悉，spring中的属性填充也是该方法完成的 * */
 getPropertyAccessor().setPropertyValues(mpvs, isIgnoreUnknownFields(), isIgnoreInvalidFields());
 }
 catch (PropertyBatchUpdateException ex) { 
 // Use bind error processor to create FieldErrors.
 for (PropertyAccessException pae : ex.getPropertyAccessExceptions()) { 
 getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult());
 }
 }
 }

### 4.6 `getPropertyAccessor()`方法，获取需要绑定对象的属性寄存器 ###

/** * Return the underlying PropertyAccessor of this binder's BindingResult. */
    protected ConfigurablePropertyAccessor getPropertyAccessor() { 
        return getInternalBindingResult().getPropertyAccessor();
    }
    
    
    /** * Return the internal BindingResult held by this DataBinder, * as an AbstractPropertyBindingResult. */
    protected AbstractPropertyBindingResult getInternalBindingResult() { 
        if (this.bindingResult == null) { 
            //初始化bean属性寄存器，见4.4
            initBeanPropertyAccess();
        }
        return this.bindingResult;
    }

> 从`4.4`中，我们知道，初始化的绑定结果类型为`BeanPropertyBindingResult`
> 
> 进入`BeanPropertyBindingResult`类的`getPropertyAccessor()`方法

/** * Returns the {@link BeanWrapper} that this instance uses. * Creates a new one if none existed before. * @see #createBeanWrapper() */
    @Override
    public final ConfigurablePropertyAccessor getPropertyAccessor() { 
        if (this.beanWrapper == null) { 
            //创建一个BeanWrapperImpl对象
            this.beanWrapper = createBeanWrapper();
            this.beanWrapper.setExtractOldValueForEditor(true);
            this.beanWrapper.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
            this.beanWrapper.setAutoGrowCollectionLimit(this.autoGrowCollectionLimit);
        }
        return this.beanWrapper;
    }
    
    
    /** * Create a new {@link BeanWrapper} for the underlying target object. * @see #getTarget() */
    protected BeanWrapper createBeanWrapper() { 
        if (this.target == null) { 
            throw new IllegalStateException("Cannot access properties on null bean instance '" + getObjectName() + "'");
        }
        //实际上就是new BeanWrapperImpl(target)
        return PropertyAccessorFactory.forBeanPropertyAccess(this.target);
    }

> 该方法本质上就是使用`new BeanWrapperImpl(需要绑定的对象)`，创建一个属性寄存器

# 5 `BeanPropertyBindingResult` #

> 用于注册和评估`javaBean`对象上的绑定错误，执行标准的`javaBean`属性访问

先来看它的类图

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 3]

## 5.1 它们拥有的字段 ##

`AbstractBindingResult`

public abstract class AbstractBindingResult extends AbstractErrors implements BindingResult, Serializable { 
 
 //要绑定参数的参数名
 private final String objectName;
 
 //消息码解析器
 private MessageCodesResolver messageCodesResolver = new DefaultMessageCodesResolver();
 
 //产生的错误对象都缓存在此处，
 private final List<ObjectError> errors = new ArrayList<>();
 
 //缓存，所有字段类型
 private final Map<String, Class<?>> fieldTypes = new HashMap<>();
 
 //缓存，所有字段属性
 private final Map<String, Object> fieldValues = new HashMap<>();
 
 private final Set<String> suppressedFields = new HashSet<>();
 }

`AbstractPropertyBindingResult`

public abstract class AbstractPropertyBindingResult extends AbstractBindingResult { 
    
        //统一转换服务
        @Nullable
        private transient ConversionService conversionService;
    }

`BeanPropertyBindingResult`

public class BeanPropertyBindingResult extends AbstractPropertyBindingResult implements Serializable { 
    
        //要绑定的参数对象
        @Nullable
        private final Object target;
    
        private final boolean autoGrowNestedPaths;
    
        private final int autoGrowCollectionLimit;
    
        @Nullable
        private transient BeanWrapper beanWrapper;
    }

### 5.1.1 `hasErrors()`方法，判断数据绑定过程中是否产生错误 ###

@Override
    public boolean hasErrors() { 
       return !this.errors.isEmpty();
    }

> 判断数据绑定过程中是否产生错误很简单，数据绑定器会把绑定错误产生的对象保存到`errors`字段中，用户只需要判断`errors`字段中是否为`null`即可知道是否产生了错误

## 5.2 构造方法 ##

/** * Creates a new instance of the {@link BeanPropertyBindingResult} class. * @param target the target bean to bind onto * @param objectName the name of the target object * @param autoGrowNestedPaths whether to "auto-grow" a nested path that contains a null value * @param autoGrowCollectionLimit the limit for array and collection auto-growing */
    public BeanPropertyBindingResult(@Nullable Object target, String objectName,
                                     boolean autoGrowNestedPaths, int autoGrowCollectionLimit) { 
    
        super(objectName);
        //要进行绑定的对象
        this.target = target;
        //是否允许处理嵌套属性
        this.autoGrowNestedPaths = autoGrowNestedPaths;
        //嵌套限制
        this.autoGrowCollectionLimit = autoGrowCollectionLimit;
    }

父类`AbstractPropertyBindingResult`构造方法

/** * Create a new AbstractPropertyBindingResult instance. * @param objectName the name of the target object * @see DefaultMessageCodesResolver */
    protected AbstractPropertyBindingResult(String objectName) { 
        super(objectName);
    }

父类`AbstractPropertyBindingResult`构造方法

/** * Create a new AbstractBindingResult instance. * @param objectName the name of the target object * @see DefaultMessageCodesResolver */
    protected AbstractBindingResult(String objectName) { 
        //最终保存参数名
        this.objectName = objectName;
    }

## 5.3 `getModel()`方法，获取绑定结果的模型数据 ##

/** * Return a model Map for the obtained state, exposing an Errors * instance as '{@link #MODEL_KEY_PREFIX MODEL_KEY_PREFIX} + objectName' * and the object itself. * Note that the Map is constructed every time you're calling this method. * Adding things to the map and then re-calling this method will not work. * The attributes in the model Map returned by this method are usually * included in the ModelAndView for a form view that uses Spring's bind tag, * which needs access to the Errors instance. * @see #getObjectName * @see #MODEL_KEY_PREFIX */
 @Override
 public Map<String, Object> getModel() { 
 Map<String, Object> model = new LinkedHashMap<>(2);
 // Mapping from name to target object.
 //绑定的参数名->要绑定的对象
 model.put(getObjectName(), getTarget());
 // Errors instance, even if no errors.
 /** * MODEL_KEY_PREFIX=org.springframework.validation.BindingResult. * 前缀+绑定的参数名->绑定结果 */
 model.put(MODEL_KEY_PREFIX + getObjectName(), this);
 return model;
 }

> 得到两个映射关系
> 
>  *  绑定的参数名->要绑定的对象
>  *  前缀+绑定的参数名->绑定结果

# 6 `ServletRequestParameterPropertyValues` #

先看类图

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 4]

> `MutablePropertyValues`我们应该很熟悉了，它内部有一个`PropertyValue`的`list`集合字段，他所有的增删改查和迭代操作都是基于这个`list`集合字段。

下面是该类的源码

public class ServletRequestParameterPropertyValues extends MutablePropertyValues { 
 
 /** Default prefix separator. */
 public static final String DEFAULT_PREFIX_SEPARATOR = "_";
 
 
 /** * Create new ServletRequestPropertyValues using no prefix * (and hence, no prefix separator). * @param request the HTTP request */
 public ServletRequestParameterPropertyValues(ServletRequest request) { 
 this(request, null, null);
 }
 
 /** * Create new ServletRequestPropertyValues using the given prefix and * the default prefix separator (the underscore character "_"). * @param request the HTTP request * @param prefix the prefix for parameters (the full prefix will * consist of this plus the separator) * @see #DEFAULT_PREFIX_SEPARATOR */
 public ServletRequestParameterPropertyValues(ServletRequest request, @Nullable String prefix) { 
 this(request, prefix, DEFAULT_PREFIX_SEPARATOR);
 }
 
 /** * Create new ServletRequestPropertyValues supplying both prefix and * prefix separator. * @param request the HTTP request * @param prefix the prefix for parameters (the full prefix will * consist of this plus the separator) * @param prefixSeparator separator delimiting prefix (e.g. "spring") * and the rest of the parameter name ("param1", "param2") */
 public ServletRequestParameterPropertyValues(
 ServletRequest request, @Nullable String prefix, @Nullable String prefixSeparator) { 
 
 //父类构造方法中将map转化为List<PropertyValue>
 super(WebUtils.getParametersStartingWith(
 request, (prefix != null ? prefix + prefixSeparator : null)));
 }
 
 }

> 该类用来封装`request`请求的请求参数，通过传入`request`对象和指定前缀，就能得到所有指定前缀的请求参数

`WebUtils.getParametersStartingWith()`方法，获取所有指定前缀的请求参数

/** * Return a map containing all parameters with the given prefix. * Maps single values to String and multiple values to String array. * For example, with a prefix of "spring_", "spring_param1" and * "spring_param2" result in a Map with "param1" and "param2" as keys. * @param request the HTTP request in which to look for parameters * @param prefix the beginning of parameter names * (if this is null or the empty string, all parameters will match) * @return map containing request parameters without the prefix, * containing either a String or a String array as values * @see javax.servlet.ServletRequest#getParameterNames * @see javax.servlet.ServletRequest#getParameterValues * @see javax.servlet.ServletRequest#getParameterMap */
 public static Map<String, Object> getParametersStartingWith(ServletRequest request, @Nullable String prefix) { 
 Assert.notNull(request, "Request must not be null");
 //获取所有请求参数名
 Enumeration<String> paramNames = request.getParameterNames();
 Map<String, Object> params = new TreeMap<>();
 if (prefix == null) { 
 prefix = "";
 }
 //遍历找到指定前缀的请求参数
 while (paramNames != null && paramNames.hasMoreElements()) { 
 String paramName = paramNames.nextElement();
 if (prefix.isEmpty() || paramName.startsWith(prefix)) { 
 String unprefixed = paramName.substring(prefix.length());
 String[] values = request.getParameterValues(paramName);
 if (values == null || values.length == 0) { 
 // Do nothing, no values found at all.
 }
 else if (values.length > 1) { 
 params.put(unprefixed, values);
 }
 else { 
 params.put(unprefixed, values[0]);
 }
 }
 }
 return params;
 }

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 2]: /images/20221024/e12b93af23a94bfabdee2e9ce0bf2e95.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMDEyOTgx_size_16_color_FFFFFF_t_70_pic_center 3]: /images/20221024/35d848a373bc4e189d8bbd3cfd448474.png
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