Java 如何使用jackson创建json数组
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how to create json array using Hymanson
提问by Victor Elizondo
I need to create a json response for a report. Something like this:
我需要为报告创建一个 json 响应。像这样的东西：
var data = [
["", "Kia", "Nissan", "Toyota", "Honda"],
["2008", 10, 11, 12, 13],
["2009", 20, 11, 14, 13],
["2010", 30, 15, 12, 13]
];
Im using Hymanson library and i create a JsonGenerator, this is the code i have:
我使用 Hymanson 库并创建了一个 JsonGenerator，这是我的代码：
String[] cols = new String[5]; //Number of report columns
JsonFactory jfactory = new JsonFactory();
JsonGenerator jGenerator = jfactory.createJsonGenerator(response.getOutputStream(),JsonEncoding.UTF8);
jGenerator.writeStartArray();
jGenerator.writeStartArray();
jGenerator.writeStringField(cols[0], "");
//until...
jGenerator.writeStringField(cols[4], "Honda");
jGenerator.writeEndArray();
jGenerator.writeStartArray();
jGenerator.writeStringField(cols[0], "2008");
//until...
jGenerator.writeStringField(cols[4], "13");
jGenerator.writeEndArray();
//and the same with the next rows...
jGenerator.writeEndArray();
The problem is when setting the first value i get this error:
问题是在设置第一个值时出现此错误：
org.codehaus.Hymanson.JsonGenerationException: Can not write a field name, expecting a value
回答by Suresh
JsonGenerator jg = new JsonFactory().createJsonGenerator(System.out);
jg.configure(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS, true);
jg.writeStartArray();
int i = 0;
while (i < 6)
{
jg.writeStartArray();
jg.writeObject(i++);
jg.writeObject(i++);
jg.writeEndArray();
}
jg.writeEndArray();
jg.flush();
OUTPUT:
输出：
[["0","1"],["2","3"],["4","5"]]
Do you need a json like this...?
你需要这样的json吗...？
回答by Chris
Can you build the array as an object before writing it, rather than bothering with all the individual pieces?
您能否在编写数组之前将其构建为一个对象，而不是费心处理所有单个部分？
ObjectMapper mapper = new ObjectMapper();
ArrayNode array = mapper.createArrayNode();
int i = 0;
while (i < 6) {
array.add(mapper.createArrayNode().add("" + i++).add("" + i++));
}
System.out.println(array);
Results in:
结果是：
[["0","1"],["2","3"],["4","5"]]
If you're not dealing with several megabytes of data or very tight memory constraints, this might turn out to be more maintainable as well.
如果您不处理几兆字节的数据或非常严格的内存限制，那么这也可能更易于维护。
