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Editor to share with you how java copies the attribute values of non-empty objects. I hope you will get something after reading this article. Let's discuss it together.

Java copies non-empty object attribute values

In many cases, we need to copy objects, such as VO class and database entity bean class, non-empty objects are not updated when updating, separate storage of different data for the same object, etc.

For object copying, both spring and Apache provide corresponding utility class methods, BeanUtils.copyProperties

But for non-empty attribute copies, you need to handle it yourself.

Borrow the methods provided by the org.springframework.beans.BeanUtils class in spring here

CopyProperties (Object source, Object target, String... IgnoreProperties)

/ * Copy the property values of the given source bean into the given target bean, * ignoring the given "ignoreProperties". *

Note: The source and target classes do not have to match or even be derived * from each other, as long as the properties match. Any bean properties that the * source bean exposes but the target bean does not will silently be ignored. *

This is just a convenience method. For more complex transfer needs, * consider using a full BeanWrapper. * @ param source the source bean * @ param target the target bean * @ param ignoreProperties array of property names to ignore * @ throws BeansException if the copying failed * @ see BeanWrapper * / public static void copyProperties (Object source, Object target, String... IgnoreProperties) throws BeansException {copyProperties (source, target, null, ignoreProperties); / * * Copy the property values of the given source bean into the given target bean. *

Note: The source and target classes do not have to match or even be derived * from each other, as long as the properties match. Any bean properties that the * source bean exposes but the target bean does not will silently be ignored. * @ param source the source bean * @ param target the target bean * @ param editable the class (or interface) to restrict property setting to * @ param ignoreProperties array of property names to ignore * @ throws BeansException if the copying failed * @ see BeanWrapper * / private static void copyProperties (Object source, Object target, Class editable, String... IgnoreProperties) throws BeansException {Assert.notNull (source, "Source must not be null"); Assert.notNull (target, "Target must not be null"); Class actualEditable = target.getClass () If (editable! = null) {if (! editable.isInstance (target)) {throw new IllegalArgumentException ("Target class [" + target.getClass (). GetName () + "] not assignable to Editable class [" + editable.getName () + "]);} actualEditable = editable;} PropertyDescriptor [] targetPds = getPropertyDescriptors (actualEditable) List ignoreList = (ignoreProperties! = null? Arrays.asList (ignoreProperties): null); for (PropertyDescriptor targetPd: targetPds) {Method writeMethod = targetPd.getWriteMethod (); if (writeMethod! = null & & (ignoreList = = null | |! ignoreList.contains (targetPd.getName () {PropertyDescriptor sourcePd = getPropertyDescriptor (source.getClass (), targetPd.getName () If (sourcePd! = null) {Method readMethod = sourcePd.getReadMethod () If (readMethod! = null & & ClassUtils.isAssignable (writeMethod.getParameterTypes () [0], readMethod.getReturnType () {try {if (! Modifier.isPublic (readMethod.getDeclaringClass (). GetModifiers () {readMethod.setAccessible (true) } Object value = readMethod.invoke (source); if (! Modifier.isPublic (writeMethod.getDeclaringClass (). GetModifiers () {writeMethod.setAccessible (true) } writeMethod.invoke (target, value);} catch (Throwable ex) {throw new FatalBeanException ("Could not copy property'" + targetPd.getName () + "'from source to target", ex) }} then encapsulate the following method / * * @ author zml2015 * @ Email zhengmingliang911@gmail.com * @ Time 5:14:25 * @ Description on February 14, 2017

Get the property name in the object whose property is null

* @ param source object to copy * @ return * / public static String [] getNullPropertyNames (Object source) {final BeanWrapper src = new BeanWrapperImpl (source); java.beans.PropertyDescriptor [] pds = src.getPropertyDescriptors (); Set emptyNames = new HashSet (); for (java.beans.PropertyDescriptor pd: pds) {Object srcValue = src.getPropertyValue (pd.getName ()) If (srcValue = = null) emptyNames.add (pd.getName ());} String [] result = new String [emptyNames.size ()]; return emptyNames.toArray (result);} / * * @ author zml2015 * @ Email zhengmingliang911@gmail.com * @ Time 14 February 2017 5:15:30 * @ Description

Copy non-empty object attribute valu

* @ param source source object * @ param target target object * / public static void copyPropertiesIgnoreNull (Object source, Object target) {BeanUtils.copyProperties (source, target, getNullPropertyNames (source));} the test method is not provided, and you can test it yourself.

If the framework used in the project has Hibernate, you can add the following two comments to the entity class

@ DynamicInsert (true) @ DynamicUpdate (true)

If you want to know more about this note, you can go to the official website to read the English document, which is explained very clearly, so I won't repeat it here.

Several ways to copy the properties of java object 1. Using the java reflection mechanism

Get the properties of the object and get, set methods to copy

two。 Use the BeanUtils class in the spring-beans5.0.8 package import org.springframework.beans.BeanUtils;SourceObject sourceObject = new SourceObject (); TargetObject targetObject = new TargetObject (); BeanUtils.copyProperties (sourceObject, targetObject); 3. Use the net.sf.cglib.beans.BeanCopier class in the cglib3.2.8 package import net.sf.cglib.beans.BeanCopier;import net.sf.cglib.core.Converter;SourceObject sourceObject = new SourceObject (); TargetObject targetObject = new TargetObject (); BeanCopier beanCopier = BeanCopier.create (SourceObject.class, TargetObject.class, true);-- the third parameter indicates whether to use the converter, false means not to use the converter, true means to use Converter converter = new CopyConverter ();-- Custom converter beanCopier.copy (sourceObject, targetObject, converter)

Converter (use the converter when the source object attribute type is inconsistent with the target object attribute type):

Import net.sf.cglib.core.Converter;import org.apache.commons.lang3.StringUtils;import java.math.BigDecimal;import java.util.Date;/** * Created by asus on 2019-7-12. * / public class CopyConverter implements Converter {@ Override public Object convert (Object value, Class target, Object context) {{String s = value.toString () If (target.equals (int.class) | | target.equals (Integer.class)) {return Integer.parseInt (s);} if (target.equals (long.class) | | target.equals (Long.class)) {return Long.parseLong (s) } if (target.equals (float.class) | | target.equals (Float.class)) {return Float.parseFloat (s);} if (target.equals (double.class) | | target.equals (Double.class)) {return Double.parseDouble (s) } if (target.equals (Date.class)) {while (s.indexOf ("-") > 0) {s = s.replace ("-", "/");} return new Date (s) } if (target.equals (BigDecimal.class)) {if (! StringUtils.isEmpty (s) & &! s.equals ("NaN")) {return new BigDecimal (s);}} return value;}} 4. Use the spring-core5.0.8 package

The org.springframework.cglib.beans.BeanCopier class in (uses the same as the third one)

Import org.springframework.cglib.beans.BeanCopier;import org.springframework.cglib.core.Converter;SourceObject sourceObject = new SourceObject (); TargetObject targetObject = new TargetObject (); Converter converter = new SpringCopyConverter (); BeanCopier beanCopier = BeanCopier.create (SourceObject.class, TargetObject.class, true); beanCopier.copy (sourceObject, targetObject, converter)

Tested for circular replication (160 attributes for source object and 160 properties for target object):

The first kind: Java reflection can copy the attribute values of common types by judging the attribute type, but the efficiency is the slowest without optimization.

Second: attribute types can not be copied at the same time, and the efficiency is relatively slow.

Third, it takes the least time. When the converter is not used, the attribute type cannot be copied at the same time. After using the converter, the time will be relatively longer.

The fourth is similar to the third, but takes a relatively long time.

After reading this article, I believe you have a certain understanding of "how java replicates non-empty object attribute values". If you want to know more about it, you are welcome to follow the industry information channel. Thank you for reading!

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