目录
1.业务场景
一种选择题试卷(TestPaper)由N个试卷项(TestPaperItem)组成,一种试卷由N个学生作答,会产生N份答卷(answer),一份答卷由N个答卷项(answerItem)组成,一个答卷项由TestPaperItem的一个问题项、一个选项组成。
实体关系如下:
相应的表关系和实体关系一直,就不赘述。
需求:
查出所有考试的答卷列表。
2.循环写法
原生写法,先获取testPaper列表,再通过testPaperId获取answer列表,再通过answerId获取answerItem列表。
整个代码就是多层嵌套循环,去拼最后的结果:
@RestController
public class TestController {
@Autowired
TestPaperService testPaperService;
@Autowired
TestPaperItemService testPaperItemService;
@Autowired
AnswerService answerService;
@Autowired
AnswerItemService answerItemService;
@GetMapping("getTestPaperList")
public List<TestPaper> getTestPaperList(){
//获取试卷列表
List<TestPaper> testPaperList = testPaperService.getList();
for (TestPaper testPaper : testPaperList) {
Answer answerQueryParam = new Answer();
answerQueryParam.setPaperId(testPaper.getId());
List<Answer> answerList = answerService.getList(answerQueryParam);
testPaper.setAnswerList(answerList);
for (Answer answer : answerList) {
AnswerItem answerItemQueryParam = new AnswerItem();
List<AnswerItem> answerItemList = answerItemService.getList(answerItemQueryParam);
answer.setAnswerItems(answerItemList);
}
}
return testPaperList;
}
}
可以看到循环写法,代码过于冗长,看起来很吃力,改起来也很吃力。
3.stream写法
接下来我们看改成stream后整个流程会多么简洁、易读:
@RestController
public class TestController {
@Autowired
TestPaperService testPaperService;
@Autowired
TestPaperItemService testPaperItemService;
@Autowired
AnswerService answerService;
@Autowired
AnswerItemService answerItemService;
@GetMapping("getTestPaperList")
public List<TestPaper> getTestPaperList() {
return testPaperService.getList().stream()
.peek(this::setAnswerList)
.collect(Collectors.toList());
}
private void setAnswerList(TestPaper testPaper) {
Answer answerQueryParam = new Answer();
answerQueryParam.setPaperId(testPaper.getId());
List<Answer> answerList = answerService.getList(answerQueryParam);
testPaper.setAnswerList(answerList);
answerList.forEach(this::setAnswerItems);
}
private void setAnswerItems(Answer answer) {
AnswerItem answerItemQueryParam = new AnswerItem();
List<AnswerItem> answerItemList = answerItemService.getList(answerItemQueryParam);
answer.setAnswerItems(answerItemList);
}
}
4.总结
通过上面的示例,我们可以看到,java stream在业务流程中,很适合当一条组装逻辑的“主线”,将冗长的代码逻辑单独剔出来封装成方法,在主线上拼接逻辑,使得代码具有优秀的可读性。这是stream在实际生产中非常重要的价值。
关于stream的更多、更详细的知识可以移步作者另一篇文章:
详解JAVA Stream__BugMan的博客-CSDN博客