Detailed explanation of Apache's object replication example tutorial

BeanUtils.copyProperties and PropertyUtils.copyProperties

Both tool classes process properties with the same name that previously existed in two beans, whether it is the source bean or the target bean. None of the attributes are processed.

The principle is to use the JDK's own reflection mechanism to dynamically get and set, thereby converting our classes.

But we should pay attention to the data types they support. Another thing is that if a class is written inside a class, which is generally called an inner class, conversion of such a class will not be successful.

The biggest difference between the two is:
1.BeanUtils.copyProperties will perform type conversion, but PropertyUtils.copyProperties will not.
Since type conversion is performed, BeanUtils.copyProperties is not as fast as PropertyUtils.copyProperties.
Therefore, the scope of application of PropertyUtils.copyProperties is slightly narrower. It only copies properties with the same name and type. If the name is the same but the type is different, it will report an error.

2. Handling of null: PropertyUtils supports null scenarios; BeanUtils does not support null scenarios for some properties, specifically as follows:

1), date type is not supported ;
2), Boolean, Ineger, Long, Short, Float, Double, etc. are not supported: Convert to false, 0;
3), string: supported, keep null;

There are several things to note when using BeanUtils:
1. For attributes of type Boolean/Short/Integer/Float/Double, it will be converted to false, 0:

 1 public class User {  
 2    3     private Integer intVal;  
 4        5     private Double doubleVal;  
 6        7     private Short shortVal;  
 8        9     private Long longVal;  
10       11     private Float floatVal;  
12       13     private Byte byteVal;  
14       15     private Boolean booleanVal;  
16 }  
17   18 User src = new User();  
19 User dest = new User();  
20 BeanUtils.copyProperties(dest, src);  
21 System.out.println(src);  
22 System.out.println(dest);  
23   24 //输出结果：      25 User [intVal=null, doubleVal=null, shortVal=null, longVal=null, floatVal=null, byteVal=null, booleanVal=null]  
26 User [intVal=0, doubleVal=0.0, shortVal=0, longVal=0, floatVal=0.0, byteVal=0, booleanVal=false]

View Code

The explanation is that these types have corresponding basic types. When performing type conversion, it is possible When encountering a conversion similar to Integer -> int, it is obvious that the attribute of type int cannot be assigned a value of null, so it is uniformly converted to 0.

How to prevent it from turning to 0? It can be like this:

1 import org.apache.commons.beanutils.converters.IntegerConverter;  
2   3 IntegerConverter converter = new IntegerConverter(null);    //默认为null，而不是0  4 BeanUtilsBean beanUtilsBean = new BeanUtilsBean();  
5 beanUtilsBean.getConvertUtils().register(converter, Integer.class);

View Code

2. For java.util.Date/BigDecimal/java.sql For the .Date/java.sql.Timestamp/java.sql.Time classes, if the value is null, an exception will be thrown during copying, and the corresponding Conveter needs to be used:

 1 public class User2 {  
 2    3     private java.util.Date javaUtilDateVal;  
 4        5     private java.sql.Date javaSqlDateVal;  
 6        7     private java.sql.Timestamp javaSqlTimeStampVal;  
 8        9     private BigDecimal bigDecimalVal;  
10   11     private java.sql.Time javaSqlTime;  
12   13 }  
14   15 User2 src = new User2();  
16 User2 dest = new User2();  
17   18 BeanUtilsBean beanUtilsBean = new BeanUtilsBean();  
19   20 //如果没有下面几行，则在转换null时会抛异常，例如：org.apache.commons.beanutils.ConversionException: No value specified for 'BigDecimal'  
21 //在org.apache.commons.beanutils.converters这个包下面有很多的Converter，可以按需要使用  22 beanUtilsBean.getConvertUtils().register(new BigDecimalConverter(null), BigDecimal.class);  
23 beanUtilsBean.getConvertUtils().register(new DateConverter(null), java.util.Date.class);  
24   25 beanUtilsBean.getConvertUtils().register(new SqlTimestampConverter(null), java.sql.Timestamp.class);  
26 beanUtilsBean.getConvertUtils().register(new SqlDateConverter(null), java.sql.Date.class);  
27 beanUtilsBean.getConvertUtils().register(new SqlTimeConverter(null), java.sql.Time.class);  
28   29 beanUtilsBean.copyProperties(dest, src);  
30 System.out.println(src);  
31 System.out.println(dest);

View Code

Assume it is copied from A to B:
Requirement 1: If a field in B has a value (not null), then the field is not copied; that is, When the field in B has no value, it will be copied, which is suitable for supplementing the value of B.

 1 import org.apache.commons.beanutils.BeanUtilsBean;  
 2 import org.apache.commons.beanutils.PropertyUtils;  
 3    4 public class CopyWhenNullBeanUtilsBean extends BeanUtilsBean{  
 5    6     @Override  
 7     public void copyProperty(Object bean, String name, Object value)  
 8             throws IllegalAccessException, InvocationTargetException {  
 9         try {  
10             Object destValue = PropertyUtils.getSimpleProperty(bean, name);  
11             if (destValue == null) {  
12                 super.copyProperty(bean, name, value);  
13             }  
14         } catch (NoSuchMethodException e) {  
15             throw new RuntimeException(e);  
16         }  
17     }  
18   19 }

Requirement 2: If a field in A has no value (is null), then the field will not be copied, that is, do not copy null is copied to B.

 1 import org.apache.commons.beanutils.BeanUtilsBean;  
 2    3 public class CopyFromNotNullBeanUtilsBean extends BeanUtilsBean {  
 4    5     @Override  
 6     public void copyProperty(Object bean, String name, Object value) throws IllegalAccessException, InvocationTargetException {  
 7         if (value == null) {  
 8             return;  
 9         }  
10         super.copyProperty(bean, name, value);  
11     }  
12 }

The above is the detailed content of Detailed explanation of Apache's object replication example tutorial. For more information, please follow other related articles on the PHP Chinese website!