淺談 SpringMVC 數據綁定

查看spring源碼可以看出spring支持轉換的數據類型：
[b]org.springframework.beans.PropertyEditorRegistrySupport[/b]:

	/**
	 * Actually register the default editors for this registry instance.
	 */
	private void createDefaultEditors() {
		this.defaultEditors = new HashMap<Class, PropertyEditor>(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);
		}
	}

下面挑選一些常用的數據類型，舉例說明它們的綁定方式

[b]1. 基本數據類型(以int爲例，其他類似)：[/b]
Controller代碼：

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

	}

JSP表單代碼：

      <form action="test.do" method="post">
         <input name="num" value="10" type="text"/>
         ......
      </form>

表單中input的name值和Controller的參數變量名保持一致，就能完成基本數據類型的數據綁定，如果不一致可以使用@RequestParam標註實現。值得一提的是，如果Controller方法參數中定義的是基本數據類型，但是從jsp提交過來的數據爲null或者""的話，會出現數據轉換的異常。也就是說，必須保證表單傳遞過來的數據不能爲null或""，所以，在開發過程中，對可能爲空的數據，最好將參數數據類型定義成包裝類型，具體參見下面的第二條。

[b]2. 包裝類型(以Integer爲例，其他類似)：[/b]
Controller代碼：

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

	}

JSP表單代碼：

      <form action="test.do" method="post">
         <input name="num" value="10" type="text"/>
         ......
      </form>

和基本數據類型基本一樣，不同之處在於，JSP表單傳遞過來的數據可以爲null或""，以上面代碼爲例，如果jsp中num爲""或者表單中無num這個input，那麼，Controller方法參數中的num值則爲null。

[b]3. 自定義對象類型：[/b]
Model代碼：

	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代碼：

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

	}

JSP表單代碼：

      <form action="test.do" method="post">
         <input name="firstName" value="張" type="text"/>
         <input name="lastName" value="三" type="text"/>
         ......
      </form>

非常簡單，只需將對象的屬性名和input的name值一一對應即可。

[b]4. 自定義複合對象類型：[/b]
Model代碼：

	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代碼：

	@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表單代碼：

      <form action="test.do" method="post">
         <input name="firstName" value="張" /><br>
         <input name="lastName" value="三" /><br>
         <input name="contactInfo.tel" value="13809908909" /><br>
         <input name="contactInfo.address" value="北京海淀" /><br>
         <input type="submit" value="Save" />
      </form>

User對象中有ContactInfo屬性，Controller中的代碼和第3點說的一致，但是，在jsp代碼中，需要使用“屬性名(對象類型的屬性).屬性名”來命名input的name。

[b]5. List綁定：[/b]
List需要綁定在對象上，而不能直接寫在Controller方法的參數中。
Model代碼：

	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<User> users;

		public List<User> getUsers() {
			return users;
		}

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

	}

Controller代碼：

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

JSP表單代碼：

      <form action="test.do" method="post">
         <table>
            <thead>
               <tr>
                  <th>First Name</th>
                  <th>Last Name</th>
               </tr>
            </thead>
            <tfoot>
               <tr>
                  <td colspan="2"><input type="submit" value="Save" /></td>
               </tr>
            </tfoot>
            <tbody>
               <tr>
                  <td><input name="users[0].firstName" value="aaa" /></td>
                  <td><input name="users[0].lastName" value="bbb" /></td>
               </tr>
               <tr>
                  <td><input name="users[1].firstName" value="ccc" /></td>
                  <td><input name="users[1].lastName" value="ddd" /></td>
               </tr>
               <tr>
                  <td><input name="users[2].firstName" value="eee" /></td>
                  <td><input name="users[2].lastName" value="fff" /></td>
               </tr>
            </tbody>
         </table>
      </form>

其實，這和第4點User對象中的contantInfo數據的綁定有點類似，但是這裏的UserListForm對象裏面的屬性被定義成List，而不是普通自定義對象。所以，在JSP中需要指定List的下標。值得一提的是，Spring會創建一個以最大下標值爲size的List對象，所以，如果JSP表單中有動態添加行、刪除行的情況，就需要特別注意，譬如一個表格，用戶在使用過程中經過多次刪除行、增加行的操作之後，下標值就會與實際大小不一致，這時候，List中的對象，只有在jsp表單中對應有下標的那些纔會有值，否則會爲null，看個例子：
JSP表單代碼：

      <form action="test.do" method="post">
         <table>
            <thead>
               <tr>
                  <th>First Name</th>
                  <th>Last Name</th>
               </tr>
            </thead>
            <tfoot>
               <tr>
                  <td colspan="2"><input type="submit" value="Save" /></td>
               </tr>
            </tfoot>
            <tbody>
               <tr>
                  <td><input name="users[0].firstName" value="aaa" /></td>
                  <td><input name="users[0].lastName" value="bbb" /></td>
               </tr>
               <tr>
                  <td><input name="users[1].firstName" value="ccc" /></td>
                  <td><input name="users[1].lastName" value="ddd" /></td>
               </tr>
               <tr>
                  <td><input name="users[20].firstName" value="eee" /></td>
                  <td><input name="users[20].lastName" value="fff" /></td>
               </tr>
            </tbody>
         </table>
      </form>

這個時候，Controller中的userForm.getUsers()獲取到List的size爲21，而且這21個User對象都不會爲null，但是，第2到第19的User對象中的firstName和lastName都爲null。打印結果：

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

[b]6. Set綁定：[/b]
Set和List類似，也需要綁定在對象上，而不能直接寫在Controller方法的參數中。但是，綁定Set數據時，必須先在Set對象中add相應的數量的模型對象。
Model代碼：

	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<User> users = new HashSet<User>();

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

		public Set<User> getUsers() {
			return users;
		}

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

	}

Controller代碼：

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

JSP表單代碼：

      <form action="test.do" method="post">
         <table>
            <thead>
               <tr>
                  <th>First Name</th>
                  <th>Last Name</th>
               </tr>
            </thead>
            <tfoot>
               <tr>
                  <td colspan="2"><input type="submit" value="Save" /></td>
               </tr>
            </tfoot>
            <tbody>
               <tr>
                  <td><input name="users[0].firstName" value="aaa" /></td>
                  <td><input name="users[0].lastName" value="bbb" /></td>
               </tr>
               <tr>
                  <td><input name="users[1].firstName" value="ccc" /></td>
                  <td><input name="users[1].lastName" value="ddd" /></td>
               </tr>
               <tr>
                  <td><input name="users[2].firstName" value="eee" /></td>
                  <td><input name="users[2].lastName" value="fff" /></td>
               </tr>
            </tbody>
         </table>
      </form>

基本和List綁定類似。
[color=red]需要特別提醒的是，如果最大下標值大於Set的size，則會拋出org.springframework.beans.InvalidPropertyException異常。[/color]所以，在使用時有些不便。暫時沒找到解決方法，如果有網友知道，請回帖共享你的做法。

[b]5. Map綁定：[/b]
Map最爲靈活，它也需要綁定在對象上，而不能直接寫在Controller方法的參數中。
Model代碼：

	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<String, User> users;

		public Map<String, User> getUsers() {
			return users;
		}

		public void setUsers(Map<String, User> users) {
			this.users = users;
		}

	}

Controller代碼：

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

JSP表單代碼：

      <form action="test.do" method="post">
         <table>
            <thead>
               <tr>
                  <th>First Name</th>
                  <th>Last Name</th>
               </tr>
            </thead>
            <tfoot>
               <tr>
                  <td colspan="2"><input type="submit" value="Save" /></td>
               </tr>
            </tfoot>
            <tbody>
               <tr>
                  <td><input name="users['x'].firstName" value="aaa" /></td>
                  <td><input name="users['x'].lastName" value="bbb" /></td>
               </tr>
               <tr>
                  <td><input name="users['y'].firstName" value="ccc" /></td>
                  <td><input name="users['y'].lastName" value="ddd" /></td>
               </tr>
               <tr>
                  <td><input name="users['z'].firstName" value="eee" /></td>
                  <td><input name="users['z'].lastName" value="fff" /></td>
               </tr>
            </tbody>
         </table>
      </form>

打印結果：

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