Spring Boot jpa Service层实现代码

package com.fei.service.impl;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Service;

import com.fei.NotFoundException;
import com.fei.po.Blog;
import com.fei.po.Type;
import com.fei.repository.BlogRepository;
import com.fei.service.BlogService;

/**
 * Created by zxf on 2019年10月3日
 */
@Service
public class BlogServiceImpl implements BlogService {

    @Autowired
    private BlogRepository blogRepository;

    /**
     * 根据id查询一条博客
     * 
     * @param id
     * @return
     */
    @Override
    public Blog getBlog(Long id) {
        return blogRepository.findById(id).get();
    }

    /**
     * 多条件动态查询博客列表
     * 
     * @param pageable
     * @param blog
     * @return
     */
    @Override
    public Page<Blog> listBlog(Pageable pageable, Blog blog) {
        return blogRepository.findAll(new Specification<Blog>() {

            @Override
            public Predicate toPredicate(Root<Blog> root, CriteriaQuery<?> cq, CriteriaBuilder cb) {
                List<Predicate> predicates = new ArrayList<>();

                String title = blog.getTitle();
                if (!"".equals(title) && title != null) {
                    predicates.add(cb.like(root.<String>get("title"), "%" + title + "%"));
                }

                Long id = blog.getType().getId();
                if (id != null) {
                    predicates.add(cb.equal(root.<Type>get("type").get("id"), id));
                }

                boolean isRecommend = blog.isRecommend();
                if (isRecommend) {
                    predicates.add(cb.equal(root.<Boolean>get("recommend"), isRecommend));
                }

                cq.where(predicates.toArray(new Predicate[predicates.size()]));
                return null;
            }
        }, pageable);
    }

    /**
     * 保存一条博客
     * 
     * @param blog
     * @return
     */
    @Override
    public Blog saveBlog(Blog blog) {
        return blogRepository.save(blog);
    }

    /**
     * 更新一条博客，先根据id查出结果回显
     * 
     * @param id
     * @param blog
     * @return
     */
    @Override
    public Blog updateBlog(Long id, Blog blog) {
        Blog b = blogRepository.findById(id).get();
        if (b == null) {
            throw new NotFoundException("你要更新的博客不存在！");
        }

        BeanUtils.copyProperties(b, blog);
        return blogRepository.save(blog);
    }

    /**
     * 根据id删除一条博客
     * 
     * @param id
     */
    @Override
    public void deleteBlog(Long id) {
        blogRepository.deleteById(id);
    }

}