} } }

    深切懂得Java:内省(Introspector)

    添加时间:2013-6-3 点击量:

      一些概念:





      内省(Introspector) 是Java 说话对 JavaBean 类属性、事务的一种缺省处理惩罚办法。


      JavaBean是一种特别的类,首要用于传递数据信息,这种类中的办法首要用于接见私有的字段,且办法名合适某种定名规矩。若是在两个模块之间传递信息,可以将信息封装进JavaBean中,这种对象称为“值对象”(Value Object),或“VO”。办法斗劲少。这些信息储存在类的私有变量中,经由过程set()、get()获得。


      例如类UserInfo :



    package com.peidasoft.Introspector;
    

    public class UserInfo {

    private long userId;
    private String userName;
    private int age;
    private String emailAddress;

    public long getUserId() {
    return userId;
    }
    public void setUserId(long userId) {
    this.userId = userId;
    }
    public String getUserName() {
    return userName;
    }
    public void setUserName(String userName) {
    this.userName = userName;
    }
    public int getAge() {
    return age;
    }
    public void setAge(int age) {
    this.age = age;
    }
    public String getEmailAddress() {
    return emailAddress;
    }
    public void setEmailAddress(String emailAddress) {
    this.emailAddress = emailAddress;
    }

    }


      在类UserInfo中有属性 userName, 那我们可以经由过程 getUserNamesetUserName来获得其值或者设置新的值。经由过程 getUserName/setUserName来接见 userName属性,这就是默认的规矩。 Java JDK中供给了一套 API 用来接见某个属性的 getter/setter 办法,这就是内省


      JDK内省类库:




      PropertyDescriptor类:


      PropertyDescriptor类默示JavaBean类经由过程存储器导出一个属性。首要办法:
          1. getPropertyType(),获得属性的Class对象;
          2. getReadMethod(),获得用于读取属性值的办法;getWriteMethod(),获得用于写入属性值的办法;
          3. hashCode(),获取对象的哈希值;
          4. setReadMethod(Method readMethod),设置用于读取属性值的办法;
          5. setWriteMethod(Method writeMethod),设置用于写入属性值的办法。


      实例代码如下:



    package com.peidasoft.Introspector;
    

    import java.beans.BeanInfo;
    import java.beans.Introspector;
    import java.beans.PropertyDescriptor;
    import java.lang.reflect.Method;

    public class BeanInfoUtil {

    public static void setProperty(UserInfo userInfo,String userName)throws Exception{
    PropertyDescriptor propDesc
    =new PropertyDescriptor(userName,UserInfo.class);
    Method methodSetUserName
    =propDesc.getWriteMethod();
    methodSetUserName.invoke(userInfo,
    wong);
    System.out.println(
    set userName:+userInfo.getUserName());
    }

    public static void getProperty(UserInfo userInfo,String userName)throws Exception{
    PropertyDescriptor proDescriptor
    =new PropertyDescriptor(userName,UserInfo.class);
    Method methodGetUserName
    =proDescriptor.getReadMethod();
    Object objUserName
    =methodGetUserName.invoke(userInfo);
    System.out.println(
    get userName:+objUserName.toString());
    }
    }


      Introspector类:


      将JavaBean中的属性封装起来进行操纵。在法度把一个类当做JavaBean来看,就是调用Introspector.getBeanInfo()办法,获得的BeanInfo对象封装了把这个类当做JavaBean看的成果信息,即属性的信息。


      getPropertyDescriptors(),获得属性的描述,可以采取遍历BeanInfo的办法,来查找、设置类的属性。具体代码如下:



    package com.peidasoft.Introspector;
    

    import java.beans.BeanInfo;
    import java.beans.Introspector;
    import java.beans.PropertyDescriptor;
    import java.lang.reflect.Method;


    public class BeanInfoUtil {

    public static void setPropertyByIntrospector(UserInfo userInfo,String userName)throws Exception{
    BeanInfo beanInfo
    =Introspector.getBeanInfo(UserInfo.class);
    PropertyDescriptor[] proDescrtptors
    =beanInfo.getPropertyDescriptors();
    if(proDescrtptors!=null&&proDescrtptors.length>0){
    for(PropertyDescriptor propDesc:proDescrtptors){
    if(propDesc.getName().equals(userName)){
    Method methodSetUserName
    =propDesc.getWriteMethod();
    methodSetUserName.invoke(userInfo,
    alan);
    System.out.println(
    set userName:+userInfo.getUserName());
    break;
    }
    }
    }
    }

    public static void getPropertyByIntrospector(UserInfo userInfo,String userName)throws Exception{
    BeanInfo beanInfo
    =Introspector.getBeanInfo(UserInfo.class);
    PropertyDescriptor[] proDescrtptors
    =beanInfo.getPropertyDescriptors();
    if(proDescrtptors!=null&&proDescrtptors.length>0){
    for(PropertyDescriptor propDesc:proDescrtptors){
    if(propDesc.getName().equals(userName)){
    Method methodGetUserName
    =propDesc.getReadMethod();
    Object objUserName
    =methodGetUserName.invoke(userInfo);
    System.out.println(
    get userName:+objUserName.toString());
    break;
    }
    }
    }
    }

    }


        经由过程这两个类的斗劲可以看出,都是须要获得PropertyDescriptor,只是体式格式不一样:前者经由过程创建对象直接获得,后者须要遍历,所以应用PropertyDescriptor类加倍便利。


      应用实例:



    package com.peidasoft.Introspector;
    

    public class BeanInfoTest {

    /
    @param args
    /
    public static void main(String[] args) {
    UserInfo userInfo
    =new UserInfo();
    userInfo.setUserName(
    peida);
    try {
    BeanInfoUtil.getProperty(userInfo,
    userName);

    BeanInfoUtil.setProperty(userInfo,
    userName);

    BeanInfoUtil.getProperty(userInfo,
    userName);

    BeanInfoUtil.setPropertyByIntrospector(userInfo,
    userName);

    BeanInfoUtil.getPropertyByIntrospector(userInfo,
    userName);

    BeanInfoUtil.setProperty(userInfo,
    age);

    }
    catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    }

    }


      输出:



    get userName:peida
    
    set userName:wong
    get userName:wong
    set userName:alan
    get userName:alan
    java.lang.IllegalArgumentException: argument type mismatch
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:
    39
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:
    25
    at java.lang.reflect.Method.invoke(Method.java:
    597
    at com.peidasoft.Introspector.BeanInfoUtil.setProperty(BeanInfoUtil.java:
    14
    at com.peidasoft.Introspector.BeanInfoTest.main(BeanInfoTest.java:
    22) 


      BeanUtils对象包:





      由上述可看出,内省操纵很是的繁琐,所以所以Apache开辟了一套简单、易用的API来操纵Bean的属性——BeanUtils对象包。
      BeanUtils对象包::http://commons.apache.org/beanutils/ 重视:应用的时辰还须要一个logging包 http://commons.apache.org/logging/
      应用BeanUtils对象包完成上方的测试代码:



    package com.peidasoft.Beanutil;
    

    import java.lang.reflect.InvocationTargetException;

    import org.apache.commons.beanutils.BeanUtils;
    import org.apache.commons.beanutils.PropertyUtils;

    import com.peidasoft.Introspector.UserInfo;

    public class BeanUtilTest {
    public static void main(String[] args) {
    UserInfo userInfo
    =new UserInfo();
    try {
    BeanUtils.setProperty(userInfo,
    userName, peida);

    System.out.println(
    set userName:+userInfo.getUserName());

    System.out.println(
    get userName:+BeanUtils.getProperty(userInfo, userName));

    BeanUtils.setProperty(userInfo,
    age, 18);
    System.out.println(
    set age:+userInfo.getAge());

    System.out.println(
    get age:+BeanUtils.getProperty(userInfo, age));

    System.out.println(
    get userName type:+BeanUtils.getProperty(userInfo, userName).getClass().getName());
    System.out.println(
    get age type:+BeanUtils.getProperty(userInfo, age).getClass().getName());

    PropertyUtils.setProperty(userInfo,
    age, 8);
    System.out.println(PropertyUtils.getProperty(userInfo,
    age));

    System.out.println(PropertyUtils.getProperty(userInfo,
    age).getClass().getName());

    PropertyUtils.setProperty(userInfo,
    age, 8);
    }
    catch (IllegalAccessException e) {
    e.printStackTrace();
    }
    catch (InvocationTargetException e) {
    e.printStackTrace();
    }
    catch (NoSuchMethodException e) {
    e.printStackTrace();
    }
    }
    }


      运行成果:



    set userName:peida
    
    get userName:peida
    set age:
    18
    get age:
    18
    get userName type:java.lang.String
    get age type:java.lang.String
    8
    java.lang.Integer
    Exception in thread
    main java.lang.IllegalArgumentException: Cannot invoke com.peidasoft.Introspector.UserInfo.setAge
    on bean
    class class com.peidasoft.Introspector.UserInfo - argument type mismatch - had objects of type java.lang.String
    but expected signature
    int
    at org.apache.commons.beanutils.PropertyUtilsBean.invokeMethod(PropertyUtilsBean.java:
    2235
    at org.apache.commons.beanutils.PropertyUtilsBean.setSimpleProperty(PropertyUtilsBean.java:
    2151
    at org.apache.commons.beanutils.PropertyUtilsBean.setNestedProperty(PropertyUtilsBean.java:
    1957
    at org.apache.commons.beanutils.PropertyUtilsBean.setProperty(PropertyUtilsBean.java:
    2064
    at org.apache.commons.beanutils.PropertyUtils.setProperty(PropertyUtils.java:
    858
    at com.peidasoft.orm.Beanutil.BeanUtilTest.main(BeanUtilTest.java:
    38
    Caused by: java.lang.IllegalArgumentException: argument type mismatch
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:
    39
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:
    25
    at java.lang.reflect.Method.invoke(Method.java:
    597
    at org.apache.commons.beanutils.PropertyUtilsBean.invokeMethod(PropertyUtilsBean.java:
    2170
    ...
    5 more


      申明:


      获得属性的值,例如,BeanUtils.getProperty(userInfo,userName),返回字符串
      设置属性的值,例如,BeanUtils.setProperty(userInfo,age,8),参数是字符串或根蒂根基类型主动包装。设置属性的值是字符串,获得的值也是字符串,不是根蒂根基类型。    BeanUtils的特点:
        1. 对根蒂根基数据类型的属性的操纵:在WEB开辟、应用中,录入和显示时,值会被转换成字符串,但底层运算用的是根蒂根基类型,这些类型转到动作由BeanUtils主动完成。
        2. 对引用数据类型的属性的操纵:起首在类中必须有对象,不克不及是null,例如,private Date birthday=new Date();。操纵的是对象的属性而不是全部对象,例如,BeanUtils.setProperty(userInfo,birthday.time,111111);   



    package com.peidasoft.Introspector;
    
    import java.util.Date;

    public class UserInfo {

    private Date birthday = new Date();

    public void setBirthday(Date birthday) {
    this.birthday = birthday;
    }
    public Date getBirthday() {
    return birthday;
    }
    }



    package com.peidasoft.Beanutil;
    

    import java.lang.reflect.InvocationTargetException;
    import org.apache.commons.beanutils.BeanUtils;
    import com.peidasoft.Introspector.UserInfo;

    public class BeanUtilTest {
    public static void main(String[] args) {
    UserInfo userInfo
    =new UserInfo();
    try {
    BeanUtils.setProperty(userInfo,
    birthday.time,111111);
    Object obj
    = BeanUtils.getProperty(userInfo, birthday.time);
    System.out.println(obj);
    }
    catch (IllegalAccessException e) {
    e.printStackTrace();
    }
    catch (InvocationTargetException e) {
    e.printStackTrace();
    }
    catch (NoSuchMethodException e) {
    e.printStackTrace();
    }
    }
    }


      PropertyUtils类和BeanUtils不合在于,运行getProperty、setProperty操纵时,没有类型转换,应用属性的原有类型或者包装类。

    无论对感情还是对生活,“只要甜不要苦”都是任性而孩子气的,因为我们也不完美,我们也会伤害人。正因为我们都不完美,也因为生活从不是事事如意,所以对这些“瑕疵”的收纳才让我们对生活、对他人的爱变得日益真实而具体。—— 汪冰《世界再亏欠你,也要敢于拥抱幸福》
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