Java反射获取对象VO的属性值（通过Getter方法）

有时候，需要动态获取对象的属性值。

比如，给你一个List，要你遍历这个List的对象的属性，而这个List里的对象并不固定。比如，这次User，下次可能是Company。

e.g. 这次我需要做一个Excel导出的工具类，导出的批量数据是以List类型传入的，List里的对象自然每次都不同，这取决于需要导出什么信息。

为了使用方便，将对象的属性名与属性值存于Map当中，使用时就可以直接遍历Map了。

此次的思路是通过反射和Getter方法取得值，然后记录在一个Map当中。

Kick start...

将对象的属性名与属性值存于Map当中，以key，value的形式存在，而value并不希望以单一类型（如String）存在（因为涉及多种类型），所以用一个FieldEntity的自定义类（此类包含属性名，属性值，属性值类型 等属性）

package com.nicchagil.util.fields;


import java.util.ArrayList;
import java.util.List;

public class FieldEntity {

    // field name
    private String fieldname;
    
    // field value
    private Object value;
    
    // field value's class type
    private Class clazz;
    
    private List<String> errorMsg = new ArrayList<String> ();

    public String getFieldname() {
        return fieldname;
    }

    public void setFieldname(String fieldname) {
        this.fieldname = fieldname;
    }

    public Object getValue() {
        return value;
    }

    public void setValue(Object value) {
        this.value = value;
    }

    public Class getClazz() {
        return clazz;
    }

    public void setClazz(Class clazz) {
        this.clazz = clazz;
    }
    
    public List<String> getErrorMsg() {
        return errorMsg;
    }

    public void setErrorMsg(List<String> errorMsg) {
        this.errorMsg = errorMsg;
    }

    public FieldEntity() {
        super();
    }

    public FieldEntity(String fieldname, Object value, Class clazz) {
        super();
        this.fieldname = fieldname;
        this.value = value;
        this.clazz = clazz;
    }

    private FieldEntity(String fieldname, List<String> errorMsg) {
        super();
        this.fieldname = fieldname;
        this.errorMsg = errorMsg;
    }

    @Override
    public String toString() {
        return "FieldEntity [fieldname=" + fieldname + ", value=" + value
                + ", clazz=" + clazz + ", errorMsg=" + errorMsg + "]";
    }
    
}

主类，通过这个类的静态方法获取结果Map

package com.nicchagil.util.fields;


import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class FieldsCollector {

    public static Map<String, FieldEntity> getFileds(Object object) 
            throws SecurityException, IllegalArgumentException, NoSuchMethodException, 
            IllegalAccessException, InvocationTargetException {
        Class clazz = object.getClass();
        Field[] fields = clazz.getDeclaredFields();
        Map<String, FieldEntity> map = new HashMap<String, FieldEntity> ();
        
        for (int i = 0; i < fields.length; i++) {
            
            Object resultObject = invokeMethod(object, fields[i].getName(), null);
            map.put(fields[i].getName(), new FieldEntity(fields[i].getName(), resultObject, fields[i].getType()));
        }
        
        return map;
    }

    public static Object invokeMethod(Object owner, String fieldname,
            Object[] args) throws SecurityException, NoSuchMethodException, 
            IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        Class ownerClass = owner.getClass();
        
        Method method = null;
        method = ownerClass.getMethod(GetterUtil.toGetter(fieldname));

        Object object = null;
        object = method.invoke(owner);

        return object;
    }

}

为了代码清楚些，将一些工具方法独立一下，如field name到getter name的转换方法

package com.nicchagil.util.fields;

public class GetterUtil {
    
    /**
     * Get getter method name by field name
     * @param fieldname
     * @return
     */
    public static String toGetter(String fieldname) {
        
        if (fieldname == null || fieldname.length() == 0) {
            return null;
        }
        
        /* If the second char is upper, make 'get' + field name as getter name. For example, eBlog -> geteBlog */
        if (fieldname.length() > 2) {
            String second = fieldname.substring(1, 2);
            if (second.equals(second.toUpperCase())) {
                return new StringBuffer("get").append(fieldname).toString();
            }
        }
        
        /* Common situation */
        fieldname = new StringBuffer("get").append(fieldname.substring(0, 1).toUpperCase())
                .append(fieldname.substring(1)).toString();
        
        return  fieldname;
    }

}

大功告成！！！

现在，写个VO作为模拟数据

import java.util.Date;

public class User {

    private String username;
    private String password;
    private String eBlog;
    private Date registrationDate;
    
    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String geteBlog() {
        return eBlog;
    }

    public void seteBlog(String eBlog) {
        this.eBlog = eBlog;
    }

    public Date getRegistrationDate() {
        return registrationDate;
    }

    public void setRegistrationDate(Date registrationDate) {
        this.registrationDate = registrationDate;
    }

}

最后，测试类，此类将直接调用FieldsCollector~~

import java.util.Date;
import java.util.Map;

import com.nicchagil.util.fields.FieldEntity;
import com.nicchagil.util.fields.FieldsCollector;



public class Call {
    
    public static void main(String[] args) throws Exception {
        
        User user = new User();
        user.setUsername("user109");
        user.setPassword("pwd109");
        user.seteBlog("http://www.cnblogs.com/nick-huang/");
        user.setRegistrationDate(new Date());
        
        Map<String, FieldEntity> map = FieldsCollector.getFileds(user);
        System.out.println(map);
        
    }

}

Oh year， 成功了~~~