浅谈 SpringMVC 数据绑定

转自: http://senton.iteye.com/blog/973918

查看spring源码可以看出spring支持转换的数据类型：
org.springframework.beans.PropertyEditorRegistrySupport:

	/**
	 * Actually register the default editors for this registry instance.
	 */
	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());
		this.defaultEditors.put(Class[].class, new ClassArrayEditor());
		this.defaultEditors.put(Currency.class, new CurrencyEditor());
		this.defaultEditors.put(File.class, new FileEditor());
		this.defaultEditors.put(InputStream.class, new InputStreamEditor());
		this.defaultEditors.put(InputSource.class, new InputSourceEditor());
		this.defaultEditors.put(Locale.class, new LocaleEditor());
		this.defaultEditors.put(Pattern.class, new PatternEditor());
		this.defaultEditors.put(Properties.class, new PropertiesEditor());
		this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
		this.defaultEditors.put(TimeZone.class, new TimeZoneEditor());
		this.defaultEditors.put(URI.class, new URIEditor());
		this.defaultEditors.put(URL.class, new URLEditor());
		this.defaultEditors.put(UUID.class, new UUIDEditor());

		// 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));

		// Default editors for primitive arrays.
		this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
		this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());

		// The JDK does not contain a default editor for char!
		this.defaultEditors.put(char.class, new CharacterEditor(false));
		this.defaultEditors.put(Character.class, new CharacterEditor(true));

		// Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor.
		this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
		this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));

		// The JDK does not contain default editors for number wrapper types!
		// Override JDK primitive number editors with our own CustomNumberEditor.
		this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false));
		this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
		this.defaultEditors.put(short.class, new CustomNumberEditor(Short.class, false));
		this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
		this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
		this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
		this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false));
		this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
		this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false));
		this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
		this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false));
		this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true));
		this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true));
		this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true));

		// Only register config value editors if explicitly requested.
		if (this.configValueEditorsActive) {
			StringArrayPropertyEditor sae = new StringArrayPropertyEditor();
			this.defaultEditors.put(String[].class, sae);
			this.defaultEditors.put(short[].class, sae);
			this.defaultEditors.put(int[].class, sae);
			this.defaultEditors.put(long[].class, sae);
		}
	}

下面挑选一些常用的数据类型，举例说明它们的绑定方式

[size=x-large]1. 基本数据类型(以int为例，其他类似)： [/size]
Controller代码：

	@RequestMapping("test.do")
	public void test(int num) {

	}

JSP表单代码：

    
  
         
       ......  
    

表单中input的name值和Controller的参数变量名保持一致，就能完成基本数据类型的数据绑定，如果不一致可以使用@RequestParam标注实现。值得一提的是，如果Controller方法参数中定义的是基本数据类型，但是从jsp提交过来的数据为null或者""的话，会出现数据转换的异常。也就是说，必须保证表单传递过来的数据不能为null或""，所以，在开发过程中，对可能为空的数据，最好将参数数据类型定义成包装类型，具体参见下面的第二条。

[size=x-large]2. 包装类型(以Integer为例，其他类似)：[/size]
Controller代码：

    @RequestMapping("test.do")  
    public void test(Integer num) {  

    }  

JSP表单代码：

    
  
         
       ......  
    
  

和基本数据类型基本一样，不同之处在于，JSP表单传递过来的数据可以为null或""，以上面代码为例，如果jsp中num为""或者表单中无num这个input，那么，Controller方法参数中的num值则为null。

[size=x-large]3. 自定义对象类型：[/size]
Model代码：

	
    public class User {  

        private String firstName;  

        private String lastName;  

        public String getFirstName() {  
            return firstName;  
        }  

        public void setFirstName(String firstName) {  
            this.firstName = firstName;  
        }  

        public String getLastName() {  
            return lastName;  
        }  

        public void setLastName(String lastName) {  
            this.lastName = lastName;  
        }  

    }  

Controller代码：

    @RequestMapping("test.do")  
    public void test(User user) {  

    }  

JSP表单代码：

    
  
         
         
       ......  
    
  

非常简单，只需将对象的属性名和input的name值一一对应即可。

[size=x-large]4. 自定义复合对象类型：[/size]
Model代码：

    public class ContactInfo {  

        private String tel;  

        private String address;  

        public String getTel() {  
            return tel;  
        }  

        public void setTel(String tel) {  
            this.tel = tel;  
        }  

        public String getAddress() {  
            return address;  
        }  

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

    }  

    public class User {  

        private String firstName;  

        private String lastName;  

        private ContactInfo contactInfo;  

        public String getFirstName() {  
            return firstName;  
        }  

        public void setFirstName(String firstName) {  
            this.firstName = firstName;  
        }  

        public String getLastName() {  
            return lastName;  
        }  

        public void setLastName(String lastName) {  
            this.lastName = lastName;  
        }  

        public ContactInfo getContactInfo() {  
            return contactInfo;  
        }  

        public void setContactInfo(ContactInfo contactInfo) {  
            this.contactInfo = contactInfo;  
        }  

    }  

Controller代码：

    @RequestMapping("test.do")  
    public void test(User user) {  
        System.out.println(user.getFirstName());  
        System.out.println(user.getLastName());  
        System.out.println(user.getContactInfo().getTel());  
        System.out.println(user.getContactInfo().getAddress());  
    }  

JSP表单代码：

User对象中有ContactInfo属性，Controller中的代码和第3点说的一致，但是，在jsp代码中，需要使用“属性名(对象类型的属性).属性名”来命名input的name。

[size=x-large]5. List绑定：[/size]
List需要绑定在对象上，而不能直接写在Controller方法的参数中。
Model代码：

    public class User {  

        private String firstName;  

        private String lastName;  

        public String getFirstName() {  
            return firstName;  
        }  

        public void setFirstName(String firstName) {  
            this.firstName = firstName;  
        }  

        public String getLastName() {  
            return lastName;  
        }  

        public void setLastName(String lastName) {  
            this.lastName = lastName;  
        }  

    }  

           public class UserListForm {  

        private List users;  //注意这里要用list, 不能使用数组, 用数组会报错. 同时也表明了为了绑定, 要多定义一个类出来. 可以把它看成是dto

        public List getUsers() {  
            return users;  
        }  

        public void setUsers(List users) {  
            this.users = users;  
        }  

    }  

Controller代码：

    @RequestMapping("test.do")  
    public void test(UserListForm userForm) {  
        for (User user : userForm.getUsers()) {  
            System.out.println(user.getFirstName() + " - " + user.getLastName());  
        }  
    }  

JSP表单代码：

    
  
       

























            
               
                  
First Name
                  
Last Name
               
            
            
               
                  
               
            
            
               
                  
                  
               
               
                  
                  
               
               
                  
                  
               
            
         
  
    
  

其实，这和第4点User对象中的contantInfo数据的绑定有点类似，但是这里的UserListForm对象里面的属性被定义成List，而不是普通自定义对象。所以，在JSP中需要指定List的下标。值得一提的是，Spring会创建一个以最大下标值为size的List对象，所以，如果JSP表单中有动态添加行、删除行的情况，就需要特别注意，譬如一个表格，用户在使用过程中经过多次删除行、增加行的操作之后，下标值就会与实际大小不一致，这时候，List中的对象，只有在jsp表单中对应有下标的那些才会有值，否则会为null，看个例子：
JSP表单代码：

    
  
       

























            
               
                  
First Name
                  
Last Name
               
            
            
               
                  
               
            
            
               
                  
                  
               
               
                  
                  
               
               
                  
                  
               
            
         
  
    
  

这个时候，Controller中的userForm.getUsers()获取到List的size为21，而且这21个User对象都不会为null，但是，第2到第19的User对象中的firstName和lastName都为null。打印结果：

    aaa - bbb  
    ccc - ddd  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    null - null  
    eee - fff  

[size=x-large]6. Set绑定：[/size]
Set和List类似，也需要绑定在对象上，而不能直接写在Controller方法的参数中。但是，绑定Set数据时，必须先在Set对象中add相应的数量的模型对象。
Model代码：

    public class User {  

        private String firstName;  

        private String lastName;  

        public String getFirstName() {  
            return firstName;  
        }  

        public void setFirstName(String firstName) {  
            this.firstName = firstName;  
        }  

        public String getLastName() {  
            return lastName;  
        }  

        public void setLastName(String lastName) {  
            this.lastName = lastName;  
        }  

    }  

    public class UserSetForm {  

        private Set users = new HashSet();  

        public UserSetForm(){  
            users.add(new User());  
            users.add(new User());  
            users.add(new User());  
        }  

        public Set getUsers() {  
            return users;  
        }  

        public void setUsers(Set users) {  
            this.users = users;  
        }  

    }  

Controller代码：

    @RequestMapping("test.do")  
    public void test(UserSetForm userForm) {  
        for (User user : userForm.getUsers()) {  
            System.out.println(user.getFirstName() + " - " + user.getLastName());  
        }  
    }  

JSP表单代码：

    
  
       

























            
               
                  
First Name
                  
Last Name
               
            
            
               
                  
               
            
            
               
                  
                  
               
               
                  
                  
               
               
                  
                  
               
            
         
  
    
  

基本和List绑定类似。
需要特别提醒的是，如果最大下标值大于Set的size，则会抛出org.springframework.beans.InvalidPropertyException异常。所以，在使用时有些不便。暂时没找到解决方法，如果有网友知道，请回帖共享你的做法。

[size=x-large]5. Map绑定：[/size]
Map最为灵活，它也需要绑定在对象上，而不能直接写在Controller方法的参数中。
Model代码：

    public class User {  

        private String firstName;  

        private String lastName;  

        public String getFirstName() {  
            return firstName;  
        }  

        public void setFirstName(String firstName) {  
            this.firstName = firstName;  
        }  

        public String getLastName() {  
            return lastName;  
        }  

        public void setLastName(String lastName) {  
            this.lastName = lastName;  
        }  

    }  

    public class UserMapForm {  

        private Map users;  

        public Map getUsers() {  
            return users;  
        }  

        public void setUsers(Map users) {  
            this.users = users;  
        }  

    }  

Controller代码：

    @RequestMapping("test.do")  
    public void test(UserMapForm userForm) {  
        for (Map.Entry entry : userForm.getUsers().entrySet()) {  
            System.out.println(entry.getKey() + ": " + entry.getValue().getFirstName() + " - " +  
                                     entry.getValue().getLastName());  
        }  
    }  

JSP表单代码：

    
  
       

























            
               
                  
First Name
                  
Last Name
               
            
            
               
                  
               
            
            
               
                  
                  
               
               
                  
                  
               
               
                  
                  
               
            
         
  
    
  

打印结果：

    x: aaa - bbb  
    y: ccc - ddd  
    z: eee - fff  

[size=x-large]当controller有两个对象时[/size]
model代码

public class Person {
    private String name;

    private int age;

    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 "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class Dog {
    private String name;
    private int age;

    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 "Dog{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

jsp代码

controller代码

@Controller
public class HelloWorldController {

    @InitBinder("person")
    protected void initBinderPerson(WebDataBinder binder) {
        binder.setFieldDefaultPrefix("person."); //注意这一行
        System.out.println("initBinderPerson ");
    }

    @InitBinder("dog")
    protected void initBinderDog(WebDataBinder binder) {
        binder.setFieldDefaultPrefix("dog."); //注意这一行
        System.out.println("initBinderDog");
    }

    @InitBinder //这个方法可以不要, 写在这里是为了说明, 每个属性的绑定前都会调用这个方法
    protected void initCommon(WebDataBinder binder) {
        System.out.println("initCommon");
    }

    @RequestMapping("/hello")
    public String hello(@ModelAttribute("dog") Dog dog, //注意这里的ModelAttribute里面的名字要跟上面的InitBinder的一致. 这样才知道是绑定哪个
                        @ModelAttribute("person") Person person,//注意这里的ModelAttribute里面的名字要跟上面的InitBinder的一致
                        @RequestParam(value = "button", defaultValue = "button1") String button,
                        Model model) {

        System.out.println("----------------");
        System.out.println(dog.toString());
        System.out.println(person.toString());

        return "helloworld";
    }

也可以不用上面的方法, 定义一个组合类包含 person类及dog类

public class ComClass{
	private Person person;
	private Dog dog;

	//get, set 方法
}

这样的话就是多定义一个类出来