优化Spring Data JPA动态查询中的多条件if-else语句

public Specification<ShapeEntity> conditionalSearch(ShapeParams shapeParams) {
    Specification spec = null;
    boolean isFirstParam = true; // 标志位，判断是否为第一个条件

    if (shapeParams.getType() != null) {
        if (isFirstParam) {
            spec = Specification.where(isTypeEqual(shapeParams.getType()));
            isFirstParam = false;
        } else {
            spec = spec.and(isTypeEqual(shapeParams.getType()));
        }
    }

    if (shapeParams.getWidthTo() != null) {
        if (isFirstParam) {
            spec = Specification.where(isWidthLessThan(shapeParams.getWidthTo()));
            isFirstParam = false;
        } else {
            spec = spec.and(isWidthLessThan(shapeParams.getWidthTo()));
        }
    }

    if (shapeParams.getWidthFrom() != null) {
        // 注意：此处假定 isWidthGreaterThan 对应 getWidthFrom
        if (isFirstParam) {
            spec = Specification.where(isWidthGreaterThan(shapeParams.getWidthFrom()));
            isFirstParam = false;
        } else {
            spec = spec.and(isWidthGreaterThan(shapeParams.getWidthFrom()));
        }
    }
    // 假设还有更多参数...
    return spec;
}

// 示例：使用 Optional 简化空值检查
Optional.ofNullable(shapeParams.getType())
        .ifPresent(type -> specs.add(isTypeEqual(type)));

import org.springframework.data.jpa.domain.Specification;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

// 假设 ShapeEntity 和 ShapeParams 是已定义的实体和参数类
// 假设 isTypeEqual, isWidthLessThan, isWidthGreaterThan 是已定义的静态 Specification 方法

public class ShapeSpecificationBuilder {

    // 假设这些是静态方法或在父类中定义
    private static Specification<ShapeEntity> isTypeEqual(String type) {
        return (root, query, criteriaBuilder) -> criteriaBuilder.equal(root.get("type"), type);
    }

    private static Specification<ShapeEntity> isWidthLessThan(Double widthTo) {
        return (root, query, criteriaBuilder) -> criteriaBuilder.lessThanOrEqualTo(root.get("width"), widthTo);
    }

    private static Specification<ShapeEntity> isWidthGreaterThan(Double widthFrom) {
        return (root, query, criteriaBuilder) -> criteriaBuilder.greaterThanOrEqualTo(root.get("width"), widthFrom);
    }

    public Specification<ShapeEntity> conditionalSearch(ShapeParams shapeParams) {
        List<Specification<ShapeEntity>> specs = new ArrayList<>();

        // 1. 使用 Optional 简化空值检查并收集条件
        Optional.ofNullable(shapeParams.getType())
                .ifPresent(type -> specs.add(isTypeEqual(type)));

        Optional.ofNullable(shapeParams.getWidthTo())
                .ifPresent(widthTo -> specs.add(isWidthLessThan(widthTo)));

        Optional.ofNullable(shapeParams.getWidthFrom())
                .ifPresent(widthFrom -> specs.add(isWidthGreaterThan(widthFrom)));

        // 2. 统一合并所有收集到的 Specification
        // 如果 specs 列表为空，表示没有提供任何查询条件。
        // 此时可以返回 null (表示不应用任何过滤)，
        // 或者返回 Specification.where(null) (表示匹配所有记录)。
        // 这里的示例选择返回 null，与原始代码行为保持一致。
        return specs.stream()
                    .reduce(Specification::and) // 使用 reduce 方法将所有条件以 AND 逻辑合并
                    .orElse(null); // 如果列表为空，则返回 null
    }

    // 示例 ShapeParams 类
    static class ShapeParams {
        private String type;
        private Double widthTo;
        private Double widthFrom;

        public String getType() { return type; }
        public void setType(String type) { this.type = type; }
        public Double getWidthTo() { return widthTo; }
        public void setWidthTo(Double widthTo) { this.widthTo = widthTo; }
        public Double getWidthFrom() { return widthFrom; }
        public void setWidthFrom(Double widthFrom) { this.widthFrom = widthFrom; }
    }

    // 示例 ShapeEntity 类
    static class ShapeEntity {
        private String type;
        private Double width;
        // ... 其他字段
        public String getType() { return type; }
        public void setType(String type) { this.type = type; }
        public Double getWidth() { return width; }
        public void setWidth(Double width) { this.width = width; }
    }
}