为什么我在解析正确的 json 响应时我的列表是空的？

Question

我正在尝试从 JSON 响应中打印 ID。但我不明白为什么我得到一个空白列表。我已经从在线网站验证了 JSON 路径 (SECTIONS_IDS_JSONPATH)，它给了我正确的结果。

public static void main(String[] args) {
    String SECTIONS_IDS_JSONPATH = "$.[*].instructionEvents[*].sectionId";
    String sectionsData = "{\"sections\":[{\"id\":\"8da1cf5d-3150-4e11-b2af-338d1df20475\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":0,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[],\"instructionEvents\":[{\"id\":\"9d0c49e2-1579-43c3-b25a-2f85f551e62d\",\"sectionId\":\"8da1cf5d-3150-4e11-b2af-338d1df20475\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"monday\",\"wednesday\",\"friday\"],\"startTm\":\"2019-01-01T09:45:00-05:00\",\"endTm\":\"2024-12-01T10:45:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]},{\"id\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":20,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[{\"id\":\"c26572de-f9c8-4623-ba6a-79997b33f1c6\",\"sectionId\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"role\":\"primary\",\"persons\":[{\"id\":\"c1b50d79-5505-4a33-9316-b4b1f52c0ca3\",\"names\":[{\"firstName\":\"BanColoFac-1\",\"lastName\":\"CTester\",\"preferred\":true}]}]}],\"instructionEvents\":[{\"id\":\"af8fb500-29f5-4451-95d5-a11215298cd4\",\"sectionId\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"tuesday\",\"thursday\"],\"startTm\":\"2019-01-01T10:00:00-05:00\",\"endTm\":\"2024-12-01T10:50:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]},{\"id\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":20,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[{\"id\":\"808daae1-3ec6-47ec-9af0-5392199bdf78\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"role\":\"primary\",\"persons\":[{\"id\":\"793cc9b3-57c7-4a2d-8984-07a1fb6834a9\",\"names\":[{\"firstName\":\"Andrew\",\"lastName\":\"Adams\",\"preferred\":true}]}]}],\"instructionEvents\":[{\"id\":\"730b4206-684d-4413-bf20-9bec5c1dc900\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"tuesday\",\"thursday\"],\"startTm\":\"2019-01-01T10:00:00-05:00\",\"endTm\":\"2024-12-01T10:50:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"},{\"id\":\"8bc059ab-a8f8-4469-8e79-bbc71f7fa3fd\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"monday\",\"wednesday\",\"friday\"],\"startTm\":\"2019-05-26T09:00:00-04:00\",\"endTm\":\"2021-05-26T09:50:00-04:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]}]}";
    List<String> ids = JsonPath.parse(sectionsData).read(SECTIONS_IDS_JSONPATH);
    System.out.println(ids);
}

Answer 1

好吧，如果没有其他事情发生，这个问题可能会被删除，所以我最好post这个作为答案。

如 Andreas 所述，您应该改用 JSONPath $.*[*].instructionEvents[*].sectionId。引用评论

The syntax $.[*] is undefined, I can't find any documentation/example doing that. The JSONPath Online Evaluator [*based on JSONPath-Plus implemented in JavaScript] treats it as $..[*], but the Java library treats it differently. Since the outer part of the JSON is {"sections":[ ... ]}, you have an object, so you need a property selector (.prop or .*). Once you've selected your property (.sections, or .* since there's only one), the property is an array, so you need an array selector ([2] or [*]). Hence you can use $.sections[*] or $.*[*] to match all sections.

确实，查看这个庞大的 JSONPath Comparision 我们可以看到没有为任何实现列出有问题的语法。

为什么我在解析正确的 json 响应时我的列表是空的？

Why my list is empty when I am parsing correct json response?

java

json

jsonpath