Why is BeanUtils not recommended?

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author ： Mingmingruyue senior
source ：blog.csdn.net/w605283073/article/details/107371462

I mentioned in the column before “ Attribute copying tools are not recommended ”, It is recommended to directly define transformation classes and methods IDEA Plug in auto fill get / set function .

The main reason for not recommending is ：

Some attribute copying tools have poor performance Some attribute copying tools have “BUG” Using the attribute copy tool is prone to some hidden dangers （ Later examples will talk about ）

2 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;@Datapublic class A {    private String name;    private List<Integer> ids;}@Datapublic 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;@Mapperpublic 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)")@Componentpublic 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.

@Overridepublic 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 ：

3 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 .

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