public
static
void
main
(
String
[] args)
{
LinkedHashMap<Integer,
String
> map =
new
LinkedHashMap<>();
map.
put
(
1
,
"A"
);
map.
put
(
3
,
"A"
);
map.
put
(
8
,
"A"
);
map.
put
(
5
,
"A"
);
System.out.
println
(
"原始顺序:"
);
for
(Object o : map.
entrySet
()) {
System.out.
printf
(
"%s "
, o);
String
fJson = JSON.
toJSONString
(map);
Map m = JSONObject.
parseObject
(fJson, Map.
class
);
System.out.
println
();
System.out.
println
(
"fastjson:"
);
for
(Object o : m.
entrySet
()) {
System.out.
printf
(
"%s "
, o);
原始顺序:
1=A 3=A 8=A 5=A
fastjson:
1=A 8=A 5=A 3=A
问题是出在fastjson的JSON.parseObject()方法上，debug代码到如下部分(版本1.1.23):
com.alibaba.fastjson.JSONObject#JSONObject()
public JSONObject() {
this(16, false);
com.alibaba.fastjson.JSONObject#JSONObject(int, boolean)
public JSONObject(int initialCapacity, boolean ordered) {
if (ordered) {
this.map = new LinkedHashMap(initialCapacity);
} else {
this.map = new AntiCollisionHashMap(initialCapacity);
由于会默认ordered = false 所以会返回一个AntiCollisionHashMap类型对象，然后用该对象去进行put赋值，返回的该map对象无法保证我们想要的顺序。
详见fastjson issue: github.com/alibaba/fas…
方法1: 采用gson将json字符串转换为map
gson实现：
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.util.LinkedHashMap;
import java.util.Map;
public class Main {
public static void main(String[] args) {
LinkedHashMap<Integer, String> map = new LinkedHashMap<>();
map.put(1, "A");
map.put(3, "A");
map.put(8, "A");
map.put(5, "A");
System.out.println("原始顺序:");
for (Object o : map.entrySet()) {
System.out.printf("%s ", o);
Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
String gJson = gson.toJson(map);
Map m = gson.fromJson(gJson, Map.class);
System.out.println();
System.out.println("gson:");
for (Object o : m.entrySet()) {
System.out.printf("%s ", o);
原始顺序:
1=A 3=A 8=A 5=A
gson:
1=A 3=A 8=A 5=A
方法2: fastjson版本升级到1.2.3以上, 指定Feature.OrderedField参数
代码示例:
//fastjson
String fJson = JSON.toJSONString(map)
Map m = JSON.parseObject(fJson, Feature.OrderedField)
System.out.println()
System.out.println("fastjson:")
for (Object o : m.entrySet()) {
System.out.printf("%s ", o)
原始顺序:
1=A 3=A 8=A 5=A
fastjson:
1=A 3=A 8=A 5=A
根据JSON.parseObject(fJson, Feature.OrderedField)，传入的Feature.OrderedField会使ordered=true，这样返回的map对象是LinkedHashMap类型，put的时候就会保证key的顺序。
com.alibaba.fastjson.JSONObject#JSONObject(int, boolean)
public JSONObject(int initialCapacity, boolean ordered) {
if (ordered) {
this.map = new LinkedHashMap(initialCapacity);
} else {
this.map = new HashMap(initialCapacity);
cloud.tencent.com/developer/a…
www.cnblogs.com/hujiapeng/p…
