我为模型映射器配置了以下配置，以将User类的实例转换为ExtendedGetUserDto的实例。
public ExtendedGetUserDto convertToExtendedDto(User user) {
PropertyMap<User, ExtendedGetUserDto> userMap = new PropertyMap<User, ExtendedGetUserDto>() {
protected void configure() {
map().setDescription(source.getDescription());
map().setId(source.getId());
// map().setReceivedExpenses(
// source.getReceivedExpenses()
// .stream()
// .map(expense -> expenseDtoConverter.convertToDto(expense))
// .collect(Collectors.toSet())
// );
Set<GetInvitationDto> result = new HashSet<GetInvitationDto>();
for (Invitation inv: source.getReceivedInvitations()) {
System.out.println("HELLO");
//result.add(null);
}
//map().setReceivedInvitations(result);
}
};
modelMapper.addMappings(userMap);
return modelMapper.map(user, ExtendedGetUserDto.class);
}
在评论setReceivedExpense之前，我收到了此错误：
org.modelmapper.ConfigurationException: ModelMapper configuration errors:
1) Invalid source method java.util.stream.Stream.map(). Ensure that method has zero parameters and does not return void.
2) Invalid source method java.util.stream.Stream.collect(). Ensure that method has zero parameters and does not return void.
2 errors
在花了一些时间而没有找到根本原因后，我试图删除DTO中所有可疑的循环依赖（我GetUserDto中引用了GetExpenseDto，expenseDtoConverter的返回结果）
我仍然收到相同的错误，我评论了map().setReceivedExpenses（正如您在代码中看到的那样）并将其替换为简单的for循环。
我收到以下错误：
1) Invalid source method java.io.PrintStream.println(). Ensure that method has zero parameters and does not return void.
为什么我会收到这些错误？
修改1
User.java
@Entity
@Table(name="User")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name="id")
private long id;
@Column(name = "name")
private String name;
@Size(min=15, max=15)
@Column(name="image_id")
private String imageId;
@Size(max=100)
@Column(name="description")
private String description;
@OneToMany(mappedBy="admin")
private Set<Group> ownedGroups;
@ManyToMany(mappedBy="members")
private Set<Group> memberGroups;
@OneToMany(cascade = CascadeType.ALL, fetch=FetchType.EAGER, mappedBy="owner")
private Set<Expense> ownedExpenses;
@ManyToMany(cascade = CascadeType.REFRESH, fetch=FetchType.EAGER)
private Set<Expense> receivedExpenses;
@OneToMany(cascade=CascadeType.ALL)
private Set<Invitation> ownedInvitations;
@OneToMany(cascade=CascadeType.ALL)
private Set<Invitation> receivedInvitations;
//setters and getters for attributes
}
ExtendedGetUserDto.java
public class ExtendedGetUserDto extends GetUserDto {
private static final long serialVersionUID = 1L;
private Set<GetInvitationDto> receivedInvitations;
private Set<GetExpenseDto> receivedExpenses;
private Set<GetExpenseDto> ownedExpenses;
private Set<GetGroupDto> ownedGroups;
private Set<GetGroupDto> memberGroups;
//setters and getters for attributes
}
答案 0 :(得分：15)
您收到这些错误是因为 PropertyMap限制了您在configure() 中可以执行的操作。
在Javadoc：
PropertyMap使用嵌入式域特定语言（EDSL）来定义源和目标方法和值如何相互映射。 Mapping EDSL允许您使用引用要映射的源和目标属性的实际代码来定义映射。 EDSL的使用在以下实例中证明。
从技术上讲，它涉及字节码分析，操作和代理，并且它需要适合此EDSL的Java方法调用。 这个聪明的技巧允许ModelMapper记录你的映射指令，并随意重放。
要了解库源代码：您得到的错误是invalidSourceMethod，抛出here in ExplicitMappingVisitor，其中ObjectMapper访问并检测configure方法的代码，使用{ {3}}
以下示例是一个独立的可运行示例，应该有助于澄清。我邀请您在ModelMapperTest.java中复制并实际运行它，然后在configure()内切换注释以重现错误：
import org.modelmapper.ModelMapper;
import org.modelmapper.PropertyMap;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class ModelMapperTest {
public static void main(String[] args) {
PropertyMap<Foo, FooDTO> propertyMap = new PropertyMap<Foo, FooDTO>() {
protected void configure() {
/* This is executed exactly ONCE, to "record" the mapping instructions.
* The bytecode of this configure() method is analyzed to produce new mapping code,
* a new dynamically-generated class with a method that will basically contain the same instructions
* that will be "replayed" each time you actually map an object later.
* But this can only work if the instructions are simple enough (ie follow the DSL).
* If you add non-compliant code here, it will break before "configure" is invoked.
* Non-compliant code is supposedly anything that does not follow the DSL.
* In practice, the framework only tracks what happens to "map()" and "source", so
* as long as print instructions do not access the source or target data (like below),
* the framework will ignore them, and they are safe to leave for debug. */
System.out.println("Entering configure()");
// This works
List<String> things = source.getThings();
map().setThingsCSVFromList(things);
// This would fail (not because of Java 8 code, but because of non-DSL code that accesses the data)
// String csv = things.stream().collect(Collectors.joining(","));
// map().setThingsCSV(csv);
System.out.println("Exiting configure()");
}
};
ModelMapper modelMapper = new ModelMapper();
modelMapper.addMappings(propertyMap);
for (int i=0; i<5; i++) {
Foo foo = new Foo();
foo.setThings(Arrays.asList("a"+i, "b"+i, "c"+i));
FooDTO dto = new FooDTO();
modelMapper.map(foo, dto); // The configure method is not re-executed, but the dynamically generated mapper method is.
System.out.println(dto.getThingsCSV());
}
}
public static class Foo {
List<String> things;
public List<String> getThings() {
return things;
}
public void setThings(List<String> things) {
this.things = things;
}
}
public static class FooDTO {
String thingsCSV;
public String getThingsCSV() {
return thingsCSV;
}
public void setThingsCSV(String thingsCSV) {
this.thingsCSV = thingsCSV;
}
public void setThingsCSVFromList(List<String> things) {
setThingsCSV(things.stream().collect(Collectors.joining(",")));
}
}
}
如果你按原样执行，你会得到：
Entering configure()
Exiting configure()
a0,b0,c0
a1,b1,c1
a2,b2,c2
a3,b3,c3
a4,b4,c4
因此，configure()只执行一次记录映射指令，然后生成的映射代码（不是configure()本身）重播 5次，每次对象映射一次。
如果您在map().setThingsCSVFromList(things)内注明configure()行，然后取消注释下面的2行＆＃34;这将失败＆＃34;，您得到：
Exception in thread "main" org.modelmapper.ConfigurationException: ModelMapper configuration errors:
1) Invalid source method java.util.stream.Stream.collect(). Ensure that method has zero parameters and does not return void.
简而言之，您无法直接在PropertyMap.configure()内执行复杂的自定义逻辑，但您可以调用的方法。这是因为框架只需要检测处理纯映射逻辑（即DSL）的字节码部分，它不关心这些方法中发生的情况。
（A - 遗留，适用于Java 6/7）严格限制DSL所要求的configure内容。例如，移动您的特殊需求＆＃34 ; （记录，收集逻辑等）到DTO本身的专用方法。
在你的情况下，将这种逻辑转移到其他地方可能会有更多的工作，但这个想法就在那里。
请注意，文档暗示PropertyMap.configure，其DSL主要用于Java 6/7，但Java 8和lambdas现在允许优雅的解决方案，其优点是不需要字节码操作魔法。
（B - Java 8）查看ASM library，例如Converter。
这是另一个例子（使用与上面相同的数据类，以及整个类型的Converter，因为这更适合我的例子，但你可以按属性执行）：
Converter<Foo, FooDTO> converter = context -> {
FooDTO dto = new FooDTO();
dto.setThingsCSV(
context.getSource().getThings().stream()
.collect(Collectors.joining(",")));
return dto;
};
ModelMapper modelMapper = new ModelMapper();
modelMapper.createTypeMap(Foo.class, FooDTO.class)
.setConverter(converter);
Foo foo = new Foo();
foo.setThings(Arrays.asList("a", "b", "c"));
FooDTO dto = modelMapper.map(foo, FooDTO.class);
System.out.println(dto.getThingsCSV()); // a,b,c