Question

我正在使用jackson-datatype-guava。我正在尝试从JSON反序列化一个表，但我得到了一个例外。

我的代码是：

@Test
public void jsonTable() throws IOException {
    Table<String, String, String> table = HashBasedTable.create();
    table.put("row1", "col1", "cell11");
    table.put("row1", "col2", "cell12");
    table.put("row2", "col1", "cell21");
    table.put("row2", "col2", "cell22");

    ObjectMapper mapper = new ObjectMapper()
            .registerModule(new GuavaModule());

    String tableJson = mapper.writeValueAsString(table);
    System.out.println(tableJson);

    Table<String, String, String> deserializedTable = mapper.readValue(tableJson, HashBasedTable.class);
}

最后一行抛出的异常是：

com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class com.google.common.collect.HashBasedTable]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: {"row1":{"col2":"cell12","col1":"cell11"},"row2":{"col2":"cell22","col1":"cell21"}}; line: 1, column: 2]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:255)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1130)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:298)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:133)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3807)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2797)
    at com.gk.dfm.repository.impl.JsonTableTest.jsonTable(JsonTableTest.java:31)

这是有道理的，因为HashBasedTable没有默认构造函数。我们应该使用HashBasedTable.create()构建它。我怎么能告诉杰克逊呢？

在this page上我找到了如何反序化Guava的Multimap：

@Test
public void convert() throws JsonParseException, JsonMappingException,
        JsonProcessingException, IOException {

    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(new GuavaModule());

    Multimap<String, NavItem> navs = objectMapper.readValue(
            objectMapper.treeAsTokens(objectMapper.readTree(jsonString)),
            objectMapper.getTypeFactory().constructMapLikeType(
                    Multimap.class, String.class, NavItem.class));

    logger.info(navs);

    assertThat(navs.keys(), hasItems("123455", "999999"));
}

如何将其应用于表格？没有constructTableLikeType这样的东西。

Answer 1

首先，尝试使用jackson-datatypes-collections而不是jackson-datatype-guava，因为it has been moved under jackson-datatype-collections to simplify management, release process.

对番石榴Table的支持似乎不完整，因为有an open issue for adding (de)serializer for it。由于它是开源的，你可以自己做（如果你这样做，请回馈！） - 你可以使用其他人写的东西，比如this pull request in old repository（也see test for Table表示支持序列化，但是虽然没有反序列化。

用Jackson反序列化Guava的表会抛出“JsonMappingException：找不到合适的类型构造函数”

1 个答案: