使用CGlib实现Bean拷贝(BeanCopier)

　　在做业务的时候，我们有时为了隔离变化，会将DAO查询出来的Entity，和对外提供的DTO隔离开来。大概90%的时候，它们的结构都是类似的，但是我们很不喜欢写很多冗长的b.setF1(a.getF1())这样的代码，于是我们需要BeanCopier来帮助我们。BeanCopier其实已经有很多开源版本，例如DozerMapper、Apache BeanUtils、Spring、Jodd BeanUtils甚至是Cglib都提供了这样的功能。下面介绍Cglib的BeanCopier的使用。

BeanCopier基本用法

public class User {
    private int age;
    private String name;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class UserDto {
    private int age;
    private String name;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class UserWithDiffType {
    private Integer age;
    private String name;

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

1. 属性名称、类型都相同:  

@Test
public void normalCopyTest() {
    // create(Class source, Class target, boolean useConverter)
    final BeanCopier beanCopier = BeanCopier.create(User.class, UserDto.class, false);
    User user = new User();
    user.setAge(10);
    user.setName("zhangsan");
    UserDto userDto = new UserDto();
    beanCopier.copy(user, userDto, null);
    Assert.assertEquals(10, userDto.getAge());
    Assert.assertEquals("zhangsan", userDto.getName());
}

结论：属性名称相同类型相同的属性拷贝OK。 

2. 属性名称相同、类型不同： 

@Test
public void normalCopyTest() {
    // create(Class source, Class target, boolean useConverter)
    final BeanCopier beanCopier = BeanCopier.create(User.class, UserWithDiffType.class, false);
    User user = new User();
    user.setAge(10);
    user.setName("zhangsan");
    UserWithDiffType userDto = new UserWithDiffType();
    beanCopier.copy(user, userDto, null);
    Assert.assertEquals(null, userDto.getAge());
    Assert.assertEquals("zhangsan", userDto.getName());
}

结论：属性名称相同而类型不同的属性不会被拷贝。  
注意：即使源类型是原始类型(int, short和char等)，目标类型是其包装类型(Integer, Short和Character等)，或反之：都 不会被拷贝。 

总结：  
BeanCopier只拷贝名称和类型都相同的属性。  

自定义转换器

当源和目标类的属性类型不同时，不能拷贝该属性，此时我们可以通过实现Converter接口来自定义转换器
源类和目标类：

public class Account {
    private int id;
    private Date createTime;
    private BigDecimal balance;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }

    public BigDecimal getBalance() {
        return balance;
    }

    public void setBalance(BigDecimal balance) {
        this.balance = balance;
    }
}

public class AccountDto {
    private int id;
    private String createTime;
    private String balance;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCreateTime() {
        return createTime;
    }

    public void setCreateTime(String createTime) {
        this.createTime = createTime;
    }

    public String getBalance() {
        return balance;
    }

    public void setBalance(String balance) {
        this.balance = balance;
    }
}

1. 不使用Converter 

@Test
public void noConverterTest() {
    Account po = new Account();
    po.setId(1);
    po.setCreateTime(new Date());
    po.setBalance(BigDecimal.valueOf(4000L));
    BeanCopier copier = BeanCopier.create(Account.class, AccountDto.class, false);
    AccountDto dto = new AccountDto();
    copier.copy(po, dto, null);
    // 类型不同，未拷贝
    Assert.assertNull(dto.getBalance());
    // 类型不同，未拷贝
    Assert.assertNull(dto.getCreateTime());
}

2. 使用Converter 
基于目标对象的属性出发，如果源对象有相同名称的属性，则调一次convert方法： 

public class TestCase {

    @Test
    public void noConverterTest() {
        Account po = new Account();
        po.setId(1);
        po.setCreateTime(new Date());
        po.setBalance(BigDecimal.valueOf(4000L));
        BeanCopier copier = BeanCopier.create(Account.class, AccountDto.class, true);
        AccountDto dto = new AccountDto();
        AccountConverter converter = new AccountConverter();
        copier.copy(po, dto, converter);
        // 类型不同，未拷贝
        Assert.assertEquals("4000", dto.getBalance());
        // 类型不同，未拷贝
        Assert.assertEquals("2018-12-13", dto.getCreateTime());
    }
}

class AccountConverter implements Converter {

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

    @SuppressWarnings("rawtypes")
    @Override
    public Object convert(Object source, Class target, Object context) {
        if (source instanceof Integer) {
            return (Integer) source;
        } else if (source instanceof Date) {
            Date date = (Date) source;
            return sdf.format(date);
        } else if (source instanceof BigDecimal) {
            BigDecimal bd = (BigDecimal) source;
            return bd.toPlainString();
        }
        return null;
    }
}

注：一旦使用Converter，BeanCopier只使用Converter定义的规则去拷贝属性，所以在convert方法中要考虑所有的属性。

封装BeanCopier

@Test
public void costTest() {
    List<User> list1 = new ArrayList<>(100);
    for (int i = 0; i < 100; i++) {
        User po = new User();
        po.setId(1);
        po.setCreateTime(new Date());
        po.setBalance(BigDecimal.valueOf(4000L));
        list1.add(po);
    }
    BeanCopier copier = BeanCopier.create(User.class, UserDto.class, false);
    long start = System.currentTimeMillis();
    List<UserDto> list2 = new ArrayList<>(100);
    for (User user : list1) {
        UserDto dto = new UserDto();
        //BeanUtils.beanCopy(user, dto);
        copier.copy(user, dto, null);
        list2.add(dto);
    }
    System.out.printf("took time: %d(ms)%n",System.currentTimeMillis() - start);
}

经过测试，BeanCopier性能是BeanUtils10倍左右。

BeanCopier拷贝速度快，性能瓶颈出现在创建BeanCopier实例的过程中。 所以，把创建过的BeanCopier实例放到缓存中，下次可以直接获取，提升性能：

public class WrappedBeanCopier {
    private static final Map<String, BeanCopier> BEAN_COPIER_CACHE = new ConcurrentHashMap<>();

    private static void copyProperties(Object source, Object target) {
        BeanCopier copier = getBeanCopier(source.getClass(), target.getClass());
        copier.copy(source, target, null);
    }

    private static BeanCopier getBeanCopier(Class sourceClass, Class targetClass) {
        String beanKey = generateKey(sourceClass, targetClass);
        BeanCopier copier = null;
        if (!BEAN_COPIER_CACHE.containsKey(beanKey)) {
            copier = BeanCopier.create(sourceClass, targetClass, false);
            BEAN_COPIER_CACHE.put(beanKey, copier);
        } else {
            copier = BEAN_COPIER_CACHE.get(beanKey);
        }
        return copier;
    }

    private static String generateKey(Class<?> sourceClass, Class<?> targetClass) {
        return sourceClass.getName() + targetClass.getName();
    }

}