How to realize the conversion between VO and DTO in java

1. Background

1. The entity classes in the domain model are divided into four types: VO, DTO, DO, PO

2. Detailed explanation

1.VO (View Object), view object, is used in the display layer. Its function is to encapsulate all the data of a specified page (or component).

2.DTO (Data Transfer Object), this concept comes from the design pattern of J2EE. The original purpose is to provide coarse-grained data entities for EJB distributed applications to reduce distributed calls. times, thereby improving the performance of distributed calls and reducing network load, but here, I generally refer to the data transfer objects used between the presentation layer and the service layer.

3.DO (Domain Object), domain object, is a tangible or intangible business entity abstracted from the real world.

4.PO (PersistentObject), persistence object, which forms a one-to-one mapping relationship with the data structure of the persistence layer (usually a relational database). If the persistence layer is a relational database, then the data Each field (or several) in the table corresponds to one (or several) attributes of PO.

5. Example:

The backend returns a front-end object, which can be ***VO.java

The dao table entity object generated by mybatis can be**** PO.java

Generally PO converts DO and then converts DTO to provide services for external calls

Note

PO is generally automatically generated and mapped one by one to table fields

DO generally has the same fields as DO, but many of the type fields are enumerations. In some projects, DO is a class ending in Model

DTO, such as the webservice interface (providing external services), returns a result object They are all DTOs. The definitions of the attributes inside are quite particular. They are easy to understand, safe and easy to expand. Whether the relationship between DTO and DTO is inclusive or parallel must be clearly defined during design, otherwise it will be a trap in the later stage.

VO comparison Simple, define whatever is needed for front-end display

3. Conversion between entity objects

A standardized project

The code is full of VO, From, DTO, DO, etc. Wait for the pojo class. These classes have different functions but the attribute values ​​​​in the class are often exactly the same. When there are many attributes, setting each one is indeed very tiring and time-consuming. In fact, the powerful Spring has already prepared thoughtful tools for us, and we can do it in one line. Even 30 lines of code

4. Specific code examples of the first method

1. Import dependencies

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-beans</artifactId>
  <version>5.1.6.RELEASE</version>
</dependency>

2. A DTO (interface definition objects generally use DTO )

public class TestDemoDTO{
    private String name;
    private Map<String,String> citys;
    private Date gmtStart;
    private Boolean flag;
    private Integer age;
    private List<String> types;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Map<String, String> getCitys() {
        return citys;
    }
 
    public void setCitys(Map<String, String> citys) {
        this.citys = citys;
    }
 
    public Date getGmtStart() {
        return gmtStart;
    }
 
    public void setGmtStart(Date gmtStart) {
        this.gmtStart = gmtStart;
    }
 
    public Boolean getFlag() {
        return flag;
    }
 
    public void setFlag(Boolean flag) {
        this.flag = flag;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public List<String> getTypes() {
        return types;
    }
 
    public void setTypes(List<String> types) {
        this.types = types;
    }
 
    @Override
    public String toString() {
        return "TestDemoDTO{" +
                "name=&#39;" + name + &#39;\&#39;&#39; +
                ", citys=" + citys +
                ", gmtStart=" + gmtStart +
                ", flag=" + flag +
                ", age=" + age +
                ", types=" + types +
                &#39;}&#39;;
    }
}

3. A From (front-end parameter definition From)

public class TestDemoFrom {
    private String name;
    private Map<String,String> citys;
    private Date gmtStart;
    private Boolean flag;
    private Integer age;
    private List<String> types;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Map<String, String> getCitys() {
        return citys;
    }
 
    public void setCitys(Map<String, String> citys) {
        this.citys = citys;
    }
 
    public Date getGmtStart() {
        return gmtStart;
    }
 
    public void setGmtStart(Date gmtStart) {
        this.gmtStart = gmtStart;
    }
 
    public Boolean getFlag() {
        return flag;
    }
 
    public void setFlag(Boolean flag) {
        this.flag = flag;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public List<String> getTypes() {
        return types;
    }
 
    public void setTypes(List<String> types) {
        this.types = types;
    }
 
    @Override
    public String toString() {
        return "TestDemoFrom{" +
                "name=&#39;" + name + &#39;\&#39;&#39; +
                ", citys=" + citys +
                ", gmtStart=" + gmtStart +
                ", flag=" + flag +
                ", age=" + age +
                ", types=" + types +
                &#39;}&#39;;
    }
}

4. Test class

public class TestDemo {
    public static void main(String[] args) {
        TestDemoFrom testDemoFrom = new TestDemoFrom();
        HashMap<String, String> map = Maps.newHashMap();
        map.put("001","北京");
        map.put("002","上海");
        map.put("003","广州");
        testDemoFrom.setCitys(map);
        testDemoFrom.setFlag(true);
        testDemoFrom.setGmtStart(new Date());
        testDemoFrom.setName("诺言");
        testDemoFrom.setAge(18);
        testDemoFrom.setTypes(Lists.newArrayList("我爱","宝贝"));
        System.out.printf(testDemoFrom.toString()+"\n");
        //下面就可以开始转化了，就一行代码
        TestDemoDTO testDemoDTO = new TestDemoDTO();
        BeanUtils.copyProperties(testDemoFrom,testDemoDTO);
 
        System.out.println(testDemoDTO.toString());
    }
}

5. Result

TestDemoFrom {name='Promise', cities={001=Beijing, 002=Shanghai, 003=Guangzhou}, gmtStart=Fri May 10 22:37:53 CST 2019, flag=true, age=18, types=[I love, Baby]}
TestDemoDTO{name='Promise', cities={001=Beijing, 002=Shanghai, 003=Guangzhou}, gmtStart=Fri May 10 22:37:53 CST 2019, flag=true, age=18 , types=[I love, baby]}

6. Note

Pay attention to the assignment failure
If the attribute names are different, the assignment will not work
If the types are different, Even if the names are the same, the value cannot be assigned.

5. Specific code examples of the second method (using dozer)

1. Import dependencies

<dependency>
  <groupId>net.sf.dozer</groupId>
  <artifactId>dozer</artifactId>
  <version>5.4.0</version>
</dependency>

2. Test class

public class TestDemoDozer {
    @Test
    public void test() {
        DozerBeanMapper mapper = new DozerBeanMapper();
        TestDemoFrom testDemoFrom = new TestDemoFrom();
        HashMap<String, String> map = Maps.newHashMap();
        map.put("001","北京");
        map.put("002","上海");
        map.put("003","广州");
        testDemoFrom.setCitys(map);
        testDemoFrom.setFlag(true);
        testDemoFrom.setGmtStart(new Date());
        testDemoFrom.setName("诺言");
        testDemoFrom.setAge(18);
        testDemoFrom.setTypes(Lists.newArrayList("我爱","宝贝"));
        System.out.printf(testDemoFrom.toString()+"\n");
        // 转换
        TestDemoDTO convert = mapper.map(testDemoFrom,TestDemoDTO.class);
        System.out.println(convert);
    }
    
}

3.Result

TestDemoFrom{name='Promise', cities={001=Beijing, 002=Shanghai, 003=Guangzhou}, gmtStart=Sat May 11 00:30:02 CST 2019, flag=true, age=18, types=[I love, baby]}
TestDemoDTO{name='Promise', cities={001=Beijing, 002=Shanghai, 003=Guangzhou}, gmtStart=Sat May 11 00:30:02 CST 2019, flag=true, age=18, types=[I love, baby]}

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