Jackson--将java列表写入json数组的最佳方法

Question

我想使用jackson将ArrayList转换为JSONArray。

event.java：这是一个java bean类，有两个字段“field1”和“field2”映射为JSONProperty。

转换

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

至

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

我能想到的方法是：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());
}

generator.write(out, list)  

generator.write(out, list1)

generator.write(out, list2)

Answer 1

这太复杂了，Jackson通过它的writer方法处理列表，就像它处理常规对象一样。假设我没有误解你的问题，这对你来说应该很好：

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));
}