杰克逊 - 最好的方法是将一个java列表写入json数组 [英] Jackson - best way writes a java list to a json array

问题描述

我想使用jackson将ArrayList转换为JsonArray。

I want to use jackson to convert a ArrayList to a JsonArray.

Event.java ：这是java bean类，有两个字段field1，field2映射为JsonProperty。

Event.java : this is the java bean class with two fields "field1", "field2" mapped as JsonProperty.

我的目标是：

转换

ArrayList<Event> list = new ArrayList<Event>();
    list.add(new Event("a1","a2"));
    list.add(new Event("b1","b2"));

到

[
{"field1":"a1", "field":"a2"},
{"field1":"b1", "field":"b2"}
]

我能想到的方式是：
writeListToJsonArray（） ：

public void writeListToJsonArray() throws IOException {  
    ArrayList<Event> list = new ArrayList<Event>();
    list.add(new Event("a1","a2"));
    list.add(new Event("b1","b2"));

    OutputStream out = new ByteArrayOutputStream();

    JsonFactory jfactory = new JsonFactory();
    JsonGenerator jGenerator = jfactory.createJsonGenerator(out, JsonEncoding.UTF8);
    ObjectMapper mapper = new ObjectMapper();
    jGenerator.writeStartArray(); // [

    for (Event event : list) {
        String e = mapper.writeValueAsString(event);
        jGenerator.writeRaw(usage);
        // here, big hassles to write a comma to separate json objects, when the last object in the list is reached, no comma 
    }

    jGenerator.writeEndArray(); // ]

    jGenerator.close();

    System.out.println(out.toString());
}

我正在寻找类似的东西：

I am looking for something like:

generator.write(out, list)  

这会直接将列表转换为json数组格式，然后将其写入outputstreamout。

this directly convert the list to json array format and then write it to outputstream "out".

甚至更贪婪：

generator.write(out, list1)

generator.write(out, list2)

这只是将list1，list2转换/添加到单个json数组中。然后将其写入out

this will just convert/add in the list1, list2 into a single json array. then write it to "out"

推荐答案

这太复杂了，杰克逊通过其编写器方法处理列表以及它处理常规对象。这应该对你有用，假设我没有误解你的问题：

This is overly complicated, Jackson handles lists via its writer methods just as well as it handles regular objects. This should work just fine for you, assuming I have not misunderstood your question:

public void writeListToJsonArray() throws IOException {  
    final List<Event> list = new ArrayList<Event>(2);
    list.add(new Event("a1","a2"));
    list.add(new Event("b1","b2"));

    final ByteArrayOutputStream out = new ByteArrayOutputStream();
    final ObjectMapper mapper = new ObjectMapper();

    mapper.writeValue(out, list);

    final byte[] data = out.toByteArray();
    System.out.println(new String(data));
}

这篇关于杰克逊 - 最好的方法是将一个java列表写入json数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！