java - Spring配置-Arraylist的可选字段

Question

我有一个包含嵌入式列表的 spring 配置类。该对象包含分隔平面文件的规范。

对于类型为decimalType 的实例，我希望在SchemaAttributes 类中具有用于精度和小数位数的可选字段。这些字段与任何其他数据类型都不相关。

如何为未提供精度/比例值的实例实现默认值？

@ConfigurationProperties(prefix = "source-parameters.file_schema")
@Configuration
public class FileSchema {

private List<SchemaAttributes> schema;

public FileSchema(List<SchemaAttributes> schema) {
    this.schema = schema;
}

public FileSchema(){

}

public List<SchemaAttributes> getSchema() {
    return schema;
}

public void setSchema(List<SchemaAttributes> schema) {
    this.schema = schema;
}


public static class SchemaAttributes {

    private String name;
    private String type;
    private Boolean nullable;
    private int precision;
    private int scale;

    public SchemaAttributes(String name, String type, Boolean nullable) {
        this.name = name;
        this.type = type;
        this.nullable = nullable;
        this.precision = precision;
        this.scale = scale;
    }

    public SchemaAttributes() {
    }

    // getters, setters

  ...
}

Answer 1

precision 和 scale 是原始 int ，因此如果构造函数未提供值 precision 和 scale 将被初始化为 0。例如:

public SchemaAttributes(String name, String type, Boolean nullable) {
    this.name = name;
    this.type = type;
    this.nullable = nullable;
    //this.precision = precision;  this.precision will be initialized to 0
    //this.scale = scale;  this.scale will be initialized to 0
}

但是委托(delegate)给另一个需要更多参数的构造函数是很常见的。例如:

public SchemaAttributes(String name, String type, Boolean nullable, int preciesion, int scale) {
    this.name = name;
    this.type = type;
    this.nullable = nullable;
    this.precision = precision;
    this.scale = scale;
}

public SchemaAttributes(String name, String type, Boolean nullable) {
    this(name, type, nullable, 0, 0);
}

public SchemaAttributes() {
    this("unknown", "unknown", true);
}

有时参数的数量变得太大和/或构造函数的数量变得太大。如果创建实例变得困难/笨重，那么请考虑转向构建器模式。