在 Lombok 中的默认值。如何使用构造函数和生成器初始化默认值

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最佳答案

My guess is that it's not possible (without having delomboked the code). But why don't you just implement the constructor you need? Lombok is meant to make your life easier, and if something won't work with Lombok, just do it the old fashioned way.

@Data
@Builder
@AllArgsConstructor
public class UserInfo {
private int id;
private String nick;
@Builder.Default
private boolean isEmailConfirmed = true;
    

public UserInfo(){
isEmailConfirmed = true;
}
}

Console output:

ui: true
ui2: true

Update
As of 01/2021, this bug seems to be fixed in Lombok, at least for generated constructors. Note that there is still a similar issue when you mix Builder.Default and explicit constructors.

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Another way is define your own getter method overriding the lombok getter:

@Data
@Builder
@AllArgsConstructor
public class UserInfo {
private int id;
private String nick;
private Boolean isEmailConfirmed;


public Boolean getIsEmailConfirmed(){
return Objects.isNull(isEmailConfirmed) ? true : isEmailConfirmed;
}
}

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Since the @Builder.Default annotation is broken, I wouldn't use it at all. You can, however, use the following approach by moving the @Builder annotation from class level to the custom constructor:

@Data
@NoArgsConstructor
public class UserInfo {


private int id;
private String nick;
private boolean isEmailConfirmed = true;


@Builder
@SuppressWarnings("unused")
private UserInfo(int id, String nick, Boolean isEmailConfirmed) {
this.id = id;
this.nick = nick;
this.isEmailConfirmed = Optional.ofNullable(isEmailConfirmed).orElse(this.isEmailConfirmed);
}
}

This way you ensure:

the field isEmailConfirmed is initialized only in one place making the code less error-prone and easier to maintain later
the UserInfo class will be initialized the same way either you use a builder or a no-args constructor

In other words, the condition holds true:

new UserInfo().equals(UserInfo.builder().build())

In that case, the object creation is consistent no matter how you create it. It is especially important when your class is used by a mapping framework or by JPA provider when you are not instantiating it manually by a builder but a no-args constructor is invoked behind your back to create the instance.

The approach described above is very similar but it has a major drawback. You have to initialize the field in two places which makes the code error-prone as you are required to keep the values consistent.

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Here's my approach :

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder(toBuilder = true)
public class UserInfo {
private int id;
private String nick;
private boolean isEmailConfirmed = true;
}

And then

UserInfo ui = new UserInfo().toBuilder().build();

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Custom constructors and @Builder.Default probably will never work together.

Framework authors want to avoid double initializations for @Builder.

I reuse .builder() by public static CLAZZ of(...) methods:

@Builder
public class Connection {
private String user;
private String pass;


@Builder.Default
private long timeout = 10_000;


@Builder.Default
private String port = "8080";


public static Connection of(String user, String pass) {
return Connection.builder()
.user(user)
.pass(pass)
.build();
}


public static Connection of(String user, String pass, String port) {
return Connection.builder()
.user(user)
.pass(pass)
.port(port)
.build();
}


public static Connection of(String user, String pass, String port, long timeout) {
return Connection.builder()
.user(user)
.pass(pass)
.port(port)
.timeout(timeout)
.build();
}
}

Check corresponding discussion: https://github.com/rzwitserloot/lombok/issues/1347

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My experience is that @Builder works best when it is the only means of instantiating a class, and therefore works best when paired with @Value rather than @Data.

For classes where all fields are mutable in any order anyway, and for which you want to keep the chained calls, consider replacing it with @Accessors(chain=true) or @Accessors(fluent=true).

@Data
@Accessors(fluent=true)
public class UserInfo {
private int id;
private String nick;
private boolean isEmailConfirmed = true;
}

This allows you to construct your objects fluently in the code, and avoid un-necessary creation of Builder objects:

UserInfo ui = new UserInfo().id(25).nick("John");

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Initialize the properties in the No-Arg Constructor

converted
private boolean isEmailConfirmed = true;

to

public class UserInfo {


public UserInfo() {
this.isEmailConfirmed = true;
}


}

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In version 1.18.2 both @NoArgsConstructor and @Builder work, but not completely.

Constructor with one or more fields will null all other default initialisations: new UserInfo("Some nick") will cause isEmailConfirmed to be false again.

My way to handle this is:

public UserInfo(String nick) {
this();
this.nick = nick;
}

This way all default fields will be initialised and we'll get expected constructor.

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You can create a static Builder class with default values populated:

@Data
@Builder(builderClassName="Builder")
@NoArgsConstructor
@AllArgsConstructor
public class UserInfo {
private int id;
private String nick;
private boolean isEmailConfirmed;
public static class Builder{
//Set defaults here
private boolean isEmailConfirmed = true;
}
}