如何过滤 json 字符串并在 Java 中获取子集 json？

Question

有没有办法过滤 JSON 字符串中的嵌套字段？

我尝试过使用 Jackson SimpleBeanPropertyFilter 进行跟踪

String jsonString = "{"
              + “\”node1\”:{“
                  + “\”field1\”:\”00\","
                  + “\”field2\”:\”test1\","
                  + “\”field3\”:\”test2\””
              + "},"
              + “\”node2\”:{“
                  + “\”field1\”:\”00\","
                  + “\”field2\”:\”test123\”,”
                  + “\”field3\”:\”test456\””
              + "}"
          + "}";

ObjectMapper mapper = new ObjectMapper()
FilterProvider filters = new SimpleFilterProvider().addFilter("filter properties by name",
                    SimpleBeanPropertyFilter.filterOutAllExcept(“field1”));
mapper.addMixIn(Object.class, PropertyFilterMixIn.class);
mapper.setFilters(filters);

它工作正常，但有没有办法在 jackson 或任何其他 Java 的 JSON 库中指定嵌套字段，如“node1.field1”？

输入

 {
  "node1": {
    "field1": "val1",
    "field2": "val2"
  },
  "node2": {
    "field1": "val1"
  }
}

过滤器

node1.field1

预期输出

{
  "node1": {
    "field1": "val1"
  }
}

Answer 1

我建议为此使用 JSON 路径。JSON 路径允许使用表达式过滤掉部分 JSON 树，例如：“$.node1[0].field1”。

为了使用 JSON 路径，您需要一个底层 JSON 库（如 Jackson），然后是这个库（Maven 语法）：

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>2.4.0</version>
</dependency>

您可以将 Jackson 作为基础库导入到您的项目中：

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.8.8</version>
</dependency>

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.8</version>
</dependency>

更新：

您可以使用 JSON 路径获取带有一些附加功能的整个节点。下面是一个使用这个表达式的例子"$.node1[?(@.field1=='00')]"：

@Test
void extractParent() {
    String jsonString = "{"
            + "\"node1\":{"
            + "\"field1\":\"00\","
            + "\"field2\":\"test1\","
            + "\"field3\":\"test2\""
            + "},"
            + "\"node2\":{"
            + "\"field1\":\"00\","
            + "\"field2\":\"test123\","
            + "\"field3\":\"test456\""
            + "}"
            + "}";
    System.out.println(jsonString);
    DocumentContext jsonPath = JsonPath.parse(jsonString);
    final JSONArray res = jsonPath.read("$.node1[?(@.field1=='00')]");
    System.out.println(res);
    Map<String, Object> composedRes = new LinkedHashMap<>();
    composedRes.put("node1", res);
    System.out.println(composedRes);
}

打印出来：

{node1=[{"field1":"00","field2":"test1","field3":"test2"}]}

这与您想要的非常接近。