BeanUtils数据转换，控制Double等数值的默认值为NULL

现象：转换Double字段NULL值字段返回的是0.0

解决方法：注册数值转换器默认值，如果自定义新的beanutils直接放新类中。

static {  
   ConvertUtils.register(new LongConverter(null), Long.class);  
   ConvertUtils.register(new ShortConverter(null), Short.class);  
   ConvertUtils.register(new IntegerConverter(null), Integer.class);  
   ConvertUtils.register(new DoubleConverter(null), Double.class);  
   ConvertUtils.register(new BigDecimalConverter(null), BigDecimal.class);  
} 

相关：在commons.beanutils.jar

1. package org.apache.commons.beanutils.ConvertUtils;

 

  public static void register(Converter converter, Class clazz) {

        ConvertUtilsBean.getInstance().register(converter, clazz);

    }

 

2.org.apache.commons.beanutils.converters.DoubleConverter;

 

    public DoubleConverter(Object defaultValue) {

        super(true, defaultValue);

    }

3.BeanUtils(本次使用的BeanUtils自定义继承自原提供的类的一个转换函数，字段是Double类型),调用转换器

 

....

org.apache.commons.beanutils.BeanUtils.populate(bean, properties);

...  

package org.apache.commons.beanutils.BeanUtilsBean（类）.populate(方法);

...

package org.apache.commons.beanutils.BeanUtilsBean.setProperty(bean, name, entry.getValue());

public void setProperty(Object bean, String name, Object value)
        throws IllegalAccessException, InvocationTargetException {

        // Trace logging (if enabled)
        ....

        // Resolve any nested expression to get the actual target bean
     ....

        // Declare local variables we will require
        String propName = resolver.getProperty(name); // Simple name of target property
        Class type = null;                            // Java type of target property
        int index  = resolver.getIndex(name);         // Indexed subscript value (if any)
        String key = resolver.getKey(name);           // Mapped key value (if any)

        // Calculate the property type
        ....

        // Convert the specified value to the required type
        Object newValue = null;
        if (type.isArray() && (index < 0)) { // Scalar value into array
            ....
        } else if (type.isArray()) {         // Indexed value into array
          ....
        } else {                             // Value into scalar
            if (value instanceof String) {
                newValue = getConvertUtils().convert((String) value, type);
            } else if (value instanceof String[]) {
                newValue = getConvertUtils().convert(((String[]) value)[0],
                                                type);
            } else {
                //测试数值型字段为null值时，为字段设置默认值
                newValue = convert(value, type);
            }
        }

        // Invoke the setter method
        try {
          getPropertyUtils().setProperty(target, name, newValue);
        } catch (NoSuchMethodException e) {
            throw new InvocationTargetException
                (e, "Cannot set " + propName);
        }

    }

 

...

....

package org.apache.commons.beanutils.converters.AbstractConverter;