Java 如何在这个for循环中使用并行流

jsonarray对象包含50000个jsonObject。我需要处理这个jsonObject来创建一个对象，然后我想将这个对象添加到列表中。这需要花费很多时间，所以我想使用并行流来创建对象并更快地添加到列表中

下面是我想用并行循环替换的代码

        // I want to insert object in this array
        List<Curriculum> curriculamList = new ArrayList<>();

        // This is the org.json array
        JSONArray jsonarray = new JSONArray(content);

        // This loop I want to replace
        for (int i = 0; i < jsonarray.length(); i++) {
            JSONObject jsonobject = jsonarray.getJSONObject(i);

            // Start of processing
            Program program = programDAO.getProgramDetails(jsonobject.getInt("programId"));
            Batch batch = batchDAO.getBatchDetails(jsonobject.getInt("batchId"), program);
            if(batch.getBatchId() == 0)
                continue;
            Major major = majorDAO.getMajorDetails(jsonobject.getInt("majorId"));
            Course course = courseDAO.getCourseDetails(jsonobject.getString("courseCode"));
            if(course == null)
                continue;
            double credits = jsonobject.getDouble("credits");
            CourseType courseType = courseTypeDAO.getCourseTypeDetails(program, jsonobject.optString("type"));
            int semesterCount = jsonobject.getInt("semester");
            String prereqCourseString = jsonobject.getString("prereq");
            Course alternateCourse = courseDAO.getCourseDetails(jsonobject.getString("alternate"));

            List<Course> prereqCourseList = new ArrayList<>();
            if (prereqCourseString.length() != 0) {
                String[] prereqCourseSplit = prereqCourseString.split("AND");
                for (String prereqCourseSplitString : prereqCourseSplit) {
                    prereqCourseList.add(courseDAO.getCourseDetails(prereqCourseSplitString.trim()));
                }
            }
            List<Course> prereqChainCourseList = new ArrayList<>();
            // End of processing

            // This is the object
            Curriculum curriculum = new Curriculum(course, credits, courseType, semesterCount, prereqCourseList, prereqChainCourseList, alternateCourse, batch, major);

            // Pushing object into the list
            curriculamList.add(curriculum);
        }

我是java新手，如果我犯了任何错误，请原谅。

Stream.ofjsonarray返回一个包含单个元素的流，即JSONArray对象，这不是您想要的

我想这就是你想要的：

List<Curriculum> curriculumList = IntStream.range(0, jsonarray.length()).parallel()
            .mapToObj(i -> {
                JSONObject jsonobject = jsonarray.getJSONObject(i);

                // fetch the various parts...

                return new Curriculum(course, credits, courseType, semesterCount, prereqCourseList, prereqChainCourseList, alternateCourse, batch, major);
            }).collect(Collectors.toList());

但是，看起来您的代码正在进行多个阻塞网络调用。使用并行流并行执行阻塞网络调用通常是不可取的，因为并行流用于CPU并行化，所以使用只有少量线程的单个共享线程池。因此，您可能更喜欢以下内容：

ExecutorService executor = Executors.newFixedThreadPool(10);

// start many calls running in parallel
List<Future<Curriculum>> futures = IntStream.range(0, jsonarray.length())
        .mapToObj(i -> executor.submit(() -> {
                JSONObject jsonobject = jsonarray.getJSONObject(i);

                // fetch the various parts...

                return new Curriculum(course, credits, courseType, semesterCount, prereqCourseList, prereqChainCourseList, alternateCourse, batch, major);
            })).collect(Collectors.toList());

executor.shutdown();

List<Curriculum> curriculumList = new ArrayList<>();
for (Future<Curriculum> future : futures) {
    curriculumList.add(future.get());
}

ofjsonarray返回一个包含单个元素的流，即JSONArray对象，这不是您想要的

我想这就是你想要的：

List<Curriculum> curriculumList = IntStream.range(0, jsonarray.length()).parallel()
            .mapToObj(i -> {
                JSONObject jsonobject = jsonarray.getJSONObject(i);

                // fetch the various parts...

                return new Curriculum(course, credits, courseType, semesterCount, prereqCourseList, prereqChainCourseList, alternateCourse, batch, major);
            }).collect(Collectors.toList());

但是，看起来您的代码正在进行多个阻塞网络调用。使用并行流并行执行阻塞网络调用通常是不可取的，因为并行流用于CPU并行化，所以使用只有少量线程的单个共享线程池。因此，您可能更喜欢以下内容：

ExecutorService executor = Executors.newFixedThreadPool(10);

// start many calls running in parallel
List<Future<Curriculum>> futures = IntStream.range(0, jsonarray.length())
        .mapToObj(i -> executor.submit(() -> {
                JSONObject jsonobject = jsonarray.getJSONObject(i);

                // fetch the various parts...

                return new Curriculum(course, credits, courseType, semesterCount, prereqCourseList, prereqChainCourseList, alternateCourse, batch, major);
            })).collect(Collectors.toList());

executor.shutdown();

List<Curriculum> curriculumList = new ArrayList<>();
for (Future<Curriculum> future : futures) {
    curriculumList.add(future.get());
}