Why is it not recommended to use BeanUtils in production?

The main reason for not recommending is ：

• Some attribute copying tools have poor performance

• Some attribute copying tools have “BUG” send

• There are some hidden dangers when using attribute copying tools （ Later examples will talk about ）

Example

First of all, the company has encountered commons Bag BeanUtils A real case of poor property copy performance , Then the colleague changed to Spring Of BeanUtils The performance is much better , If you are interested, you can use the performance test framework or benchmark framework to compare , There is no comparison here .

Now let's see Spring Of BeanUtils What are the problems with copying the properties of ：

import lombok.Data;
import java.util.List;
 
@Data
public class A {
    private String name;
 
    private List<Integer> ids;
}

@Data
public class B {
    private String name;
 
    private List<String> ids;
}

import org.springframework.beans.BeanUtils;
 
import java.util.Arrays;
 
public class BeanUtilDemo {
    public static void main(String[] args) {
        A first = new A();
        first.setName("demo");
        first.setIds(Arrays.asList(1, 2, 3));
 
        B second = new B();
        BeanUtils.copyProperties(first, second);
        for (String each : second.getIds()) {//  Type conversion exception 
            System.out.println(each);
        }
    }
}

When you run the above example , A type conversion exception occurs .

At the break point, you can see , After the attribute is copied B Type of second In the object ids Still for Integer type ：

If not converted to a string , Print directly , No errors are reported .

Use CGlib Not defined in Converter Similar problems will be encountered in the case of ：

import org.easymock.cglib.beans.BeanCopier;
 
import java.util.Arrays;
 
public class BeanUtilDemo {
    public static void main(String[] args) {
        A first = new A();
        first.setName("demo");
        first.setIds(Arrays.asList(1, 2, 3));
 
        B second = new B();
        final BeanCopier beanCopier = BeanCopier.create(A.class, B.class, false);
        beanCopier.copy(first,second,null);
 
        for (String each : second.getIds()) {//  Type conversion exception 
            System.out.println(each);
        }
    }
}

Again , The problem is exposed at runtime .

Let's take a look mapstruct：

import org.mapstruct.Mapper;
import org.mapstruct.factory.Mappers;
 
@Mapper
public interface Converter {
    Converter INSTANCE = Mappers.getMapper(Converter.class);
 
    B aToB(A car);
}

import java.util.Arrays;
 
public class BeanUtilDemo {
    public static void main(String[] args) {
        A first = new A();
        first.setName("demo");
        first.setIds(Arrays.asList(1, 2, 3));
 
        B second = Converter.INSTANCE.aToB(first);
        for (String each : second.getIds()) {//  normal 
            System.out.println(each);
        }
    }
}

Can succeed in A in List<Integer> To B Medium List<String> type .

Let's look at the compiled Converter Implementation class ：

import java.util.ArrayList;
import java.util.List;
import javax.annotation.Generated;
import org.springframework.stereotype.Component;
 
@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    comments = "version: 1.3.1.Final, compiler: javac, environment: Java 1.8.0_202 (Oracle Corporation)"
)
@Component
public class ConverterImpl implements Converter {
 
    @Override
    public B aToB(A car) {
        if ( car == null ) {
            return null;
        }
 
        B b = new B();
 
        b.setName( car.getName() );
        b.setIds( integerListToStringList( car.getIds() ) );
 
        return b;
    }
 
    protected List<String> integerListToStringList(List<Integer> list) {
        if ( list == null ) {
            return null;
        }
 
        List<String> list1 = new ArrayList<String>( list.size() );
        for ( Integer integer : list ) {
            list1.add( String.valueOf( integer ) );
        }
 
        return list1;
    }
}

Automatically helped us with the conversion , We may not realize that the types are inconsistent .

If we were A Add one to the class String number attribute , stay B Add one to the class Long number attribute , Use mapstruect When number When it is set to non numeric type, it will report .NumberFormatException.

@Override
public B aToB(A car) {
    if ( car == null ) {
        return null;
    }
 
    B b = new B();
 
    b.setName( car.getName() );
    if ( car.getNumber() != null ) { //  Here's the problem 
        b.setNumber( Long.parseLong( car.getNumber() ) );
    }
    b.setIds( integerListToStringList( car.getIds() ) );
 
    return b;
}

Use cglib By default, there is no mapping number attribute ,B Medium number by null.

If you define the converter manually , Use IDEA plug-in unit ( Such as generateO2O) Automatic conversion ：

public final class A2BConverter {
 
    public static B from(A first) {
        B b = new B();
        b.setName(first.getName());
        b.setIds(first.getIds());
        return b;
    }
}

This problem can be found very clearly in the coding phase ：

Conclusion

because Java Generics are actually compile time checks , Post compilation generic erasure , Causes the runtime to List<Integer> and List<String> All are List type , It can be assigned normally . This leads to when using many attribute mapping tools , It is not easy to make obvious errors at compile time .

mapstruct Custom annotation processor , The generic types on both sides of the map can be read at compile time , Then map . But this mapping is also terrible , Sometimes we define the wrong type due to carelessness and other reasons , Automatically helped us with the conversion , It will bring a lot of side effects .

The performance of various attribute mapping tools has been briefly compared before , give the result as follows ：

Therefore, use attribute conversion tools with caution , If possible, it is recommended to customize the conversion class , Use IDEA Plug in auto fill , Very efficient , A or B Any property type in does not match , Even delete an attribute , Errors can be reported at the compilation stage , And directly call get set The efficiency is also very high , I hope I can help you ！