java 使用反射比较字段值
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Comparing field values using reflection
提问by JonH
I am trying to compare the field values of two different objects in a generic way. I have a function (seen below) that takes in two Objects and then gets the fields and then compares the fields in a loop and adds the fields to a list if they are not the same - is this the proper way to do this?
我正在尝试以通用方式比较两个不同对象的字段值。我有一个函数（见下文），它接收两个对象，然后获取字段，然后在循环中比较字段，如果字段不相同，则将字段添加到列表中 - 这是执行此操作的正确方法吗？
public void compareFields(Object qa, Object qa4) throws FieldsNotEqualException
{
Field[] qaFields = qa.getClass().getFields();
Field[] qa4Fields = qa4.getClass().getFields();
for(Field f:qaFields)
{
for(Field f4:qa4Fields)
{
if(f4.equals(f))
{
found = true;
break;
}
else
{
continue;
}
}
}
if(!found)
{
report.add(/*some_formatted_string*/) //some global list
throw new FieldsNotEqualException();
}
}
I was googling and I saw that C# had like a PropertyInfo Class - does Java have anything like that?
ALSO, is there a way to do like f.getFieldValue()-I know there is no method like this but maybe there is another way???
我在谷歌上搜索，我看到 C# 有一个 PropertyInfo 类——Java 有类似的东西吗？另外，有没有办法这样做f.getFieldValue()- 我知道没有这样的方法，但也许还有另一种方法？？？
回答by tjg184
You might check out org.apache.commons.lang.builder.EqualsBuilder which will save you a lot of this hassle if you're wanting to do a field by field comparison.
如果您想逐个字段进行比较，您可以查看 org.apache.commons.lang.builder.EqualsBuilder，这将为您省去很多麻烦。
org.apache.commons.lang.builder.EqualsBuilder.reflectionEquals(Object, Object)
If you're wanting to compare fields yourself, check out java.lang.Class.getDeclaredFields()which will give you all the fields including non-public fields.
如果您想自己比较字段，请查看java.lang.Class.getDeclaredFields()这将为您提供所有字段，包括非公共字段。
To compare the value of the fields use f.get(qa).equals(f.get(qa4))Currently, you are actually comparing the field instances and not the values.
要比较字段的值，请使用f.get(qa).equals(f.get(qa4))Current，您实际上是在比较字段实例而不是值。
回答by Costi Ciudatu
Libraries like commons-beanutilscan help you if you want to compare bean properties (values returned by getters) instead of comparing field values.
如果您想比较 bean 属性（由 getter 返回的值）而不是比较字段值，像commons-beanutils这样的库可以帮助您。
However, if you want to stick with plain reflection, you should:
但是，如果您想坚持使用简单的反射，您应该：
- Use
Class.getDeclaredFields()instead ofClass.getFields(), as the latter only returns the public fields. - Since fields only depend on their class, you should cache the result and keep the fields in a static / instance variable rather than invoking
getDeclaredFields()for each comparison. - Once you have an object of that class (say
o), in order to get the value of some fieldffor that particular object, you need to call:f.get(o).
- 使用
Class.getDeclaredFields()代替Class.getFields()，因为后者只返回公共字段。 - 由于字段仅依赖于它们的类，因此您应该缓存结果并将字段保存在静态/实例变量中，而不是
getDeclaredFields()为每个比较调用。 - 一旦您拥有该类的对象（例如
o），为了获取该f特定对象的某个字段的值，您需要调用：f.get(o)。
回答by Ahmed Ali
// If you want to have some fields, not all field then use this.
// 如果你想要一些字段，而不是所有字段，那么使用这个。
public boolean compareObject(Object object) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException
{
String[] compareFields = { "fieldx", "fieldy","fieldz", "field15",
"field19"}; // list of all we need
for(String s : compareFields) {
Field field = DcrAttribute.class.getDeclaredField(s); // get a list of all fields for this class
field.setAccessible(true);
if(!field.get(this).equals(field.get(object))){ //if values are not equal
return true;
}
}
return false;
}
