淺談 SpringMVC 資料繫結

查看spring源碼可以看出spring支援轉換的資料類型：
org.springframework.beans.PropertyEditorRegistrySupport:

/** * 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資料類型，舉例說明它們的綁定方式

1. 基礎資料型別 (Elementary Data Type)(以int為例，其他類似)：
    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的參數變數名保持一致，就能完成基礎資料型別 (Elementary Data Type)的資料繫結，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礎資料型別 (Elementary Data Type)，但是從jsp提交過來的資料為null或者""的話，會出現資料轉換的異常。也就是說，必須保證表單傳遞過來的資料不能為null或""，所以，在開發過程中，對可能為空白的資料，最好將參數資料類型定義成封裝類型，具體參見下面的第二條。

2. 封裝類型(以Integer為例，其他類似)：
    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>

和基礎資料型別 (Elementary Data Type)基本一樣，不同之處在於，JSP表單傳遞過來的資料可以為null或""，以上面代碼為例，如果jsp中num為""或者表單中無num這個input，那麼，Controller方法參數中的num值則為null。

3. 自訂物件類型：
    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稱和input的name值一一對應即可。

4. 自訂綜合物件類型：
    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="北京海澱" /><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“屬性名稱(物件類型的屬性).屬性名稱”來命名input的name。

5. List綁定：
    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資料的綁定有點類似，但是這裡的UserListForm對象裡面的屬性被定義成List，而不是普通自訂對象。所以，在JSP中需要指定List的下標。值得一提的是，Spring會建立一個以最大下標值為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，使用者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才會有值，否則會為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()擷取到List的size為21，而且這21個User對象都不會為null，但是，第2到第19的User對象中的firstName和lastName都為null。列印結果：

aaa - bbbccc - dddnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nullnull - nulleee - fff

6. Set綁定：
    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資料時，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。
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。所以，在使用時有些不便。暫時沒找到解決方案，如果有網友知道，請回帖共用你的做法。

5. Map綁定：
    Map最為靈活，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>

列印結果：

x: aaa - bbby: ccc - dddz: eee - fff