我有以下JSON文本。我如何解析它以获得pageName, pagePic, post_id等的值?
{
"pageInfo": {
"pageName": "abc",
"pagePic": "http://example.com/content.jpg"
},
"posts": [
{
"post_id": "123456789012_123456789012",
"actor_id": "1234567890",
"picOfPersonWhoPosted": "http://example.com/photo.jpg",
"nameOfPersonWhoPosted": "Jane Doe",
"message": "Sounds cool. Can't wait to see it!",
"likesCount": "2",
"comments": [],
"timeOfPost": "1234567890"
}
]
}
当前回答
我们可以使用JSONObject类将JSON字符串转换为JSON对象， 和遍历JSON对象。使用下面的代码。
JSONObject jObj = new JSONObject(contents.trim());
Iterator<?> keys = jObj.keys();
while( keys.hasNext() ) {
String key = (String)keys.next();
if ( jObj.get(key) instanceof JSONObject ) {
System.out.println(jObj.getString(String key));
}
}
其他回答
Java中有许多可用的JSON库。
最臭名昭著的是:Jackson, GSON, Genson, FastJson和org.json。
在选择任何库时，通常应该注意以下三点:
性能 易于使用(代码写起来简单易读)——这与功能有关。 对于移动应用:依赖/jar大小
特别是对于JSON库(以及任何序列化/反序列化库)，数据绑定通常也很有趣，因为它消除了编写样板代码来打包/解包数据的需要。
对于1，看到这个基准:https://github.com/fabienrenaud/java-json-benchmark我做了使用JMH比较(杰克逊，gson, genson, fastjson, org。使用stream和databind api实现序列化器和反序列化器的性能。 第二，你可以在网上找到很多例子。上面的基准测试也可以作为例子的来源。
快速总结一下基准:杰克逊的表现比组织好5到6倍。json，比GSON好两倍以上。
对于您的特定示例，下面的代码将使用jackson解码json:
public class MyObj {
private PageInfo pageInfo;
private List<Post> posts;
static final class PageInfo {
private String pageName;
private String pagePic;
}
static final class Post {
private String post_id;
@JsonProperty("actor_id");
private String actorId;
@JsonProperty("picOfPersonWhoPosted")
private String pictureOfPoster;
@JsonProperty("nameOfPersonWhoPosted")
private String nameOfPoster;
private String likesCount;
private List<String> comments;
private String timeOfPost;
}
private static final ObjectMapper JACKSON = new ObjectMapper();
public static void main(String[] args) throws IOException {
MyObj o = JACKSON.readValue(args[0], MyObj.class); // assumes args[0] contains your json payload provided in your question.
}
}
如果你有任何问题请告诉我。
由于还没有人提到它，这里是一个使用Nashorn (Java 8的JavaScript运行时部分，但在Java 11中已弃用)的解决方案的开始。
解决方案
private static final String EXTRACTOR_SCRIPT =
"var fun = function(raw) { " +
"var json = JSON.parse(raw); " +
"return [json.pageInfo.pageName, json.pageInfo.pagePic, json.posts[0].post_id];};";
public void run() throws ScriptException, NoSuchMethodException {
ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
engine.eval(EXTRACTOR_SCRIPT);
Invocable invocable = (Invocable) engine;
JSObject result = (JSObject) invocable.invokeFunction("fun", JSON);
result.values().forEach(e -> System.out.println(e));
}
性能比较
我编写的JSON内容包含三个数组，分别为20、20和100个元素。我只想从第三个数组中获取100个元素。我使用下面的JavaScript函数来解析和获取我的条目。
var fun = function(raw) {JSON.parse(raw).entries};
使用Nashorn运行一百万次调用需要7.5~7.8秒
(JSObject) invocable.invokeFunction("fun", json);
org。Json需要20~21秒
new JSONObject(JSON).getJSONArray("entries");
杰克逊用时6.5~7秒
mapper.readValue(JSON, Entries.class).getEntries();
在这种情况下，Jackson的性能比Nashorn好，后者的性能比org.json好得多。 Nashorn API比org更难使用。json或Jackson的。根据您的需求，Jackson和Nashorn都是可行的解决方案。
If one wants to create Java object from JSON and vice versa, use GSON or JACKSON third party jars etc. //from object to JSON Gson gson = new Gson(); gson.toJson(yourObject); // from JSON to object yourObject o = gson.fromJson(JSONString,yourObject.class); But if one just want to parse a JSON string and get some values, (OR create a JSON string from scratch to send over wire) just use JaveEE jar which contains JsonReader, JsonArray, JsonObject etc. You may want to download the implementation of that spec like javax.json. With these two jars I am able to parse the json and use the values. These APIs actually follow the DOM/SAX parsing model of XML. Response response = request.get(); // REST call JsonReader jsonReader = Json.createReader(new StringReader(response.readEntity(String.class))); JsonArray jsonArray = jsonReader.readArray(); ListIterator l = jsonArray.listIterator(); while ( l.hasNext() ) { JsonObject j = (JsonObject)l.next(); JsonObject ciAttr = j.getJsonObject("ciAttributes");
如果你的数据很简单，你不想要外部依赖，可以使用以下几行代码:
/**
* A very simple JSON parser for one level, everything quoted.
* @param json the json content.
* @return a key => value map.
*/
public static Map<String, String> simpleParseJson(String json) {
Map<String, String> map = new TreeMap<>();
String qs[] = json.replace("\\\"", "\u0001").replace("\\\\", "\\").split("\"");
for (int i = 1; i + 3 < qs.length; i += 4) {
map.put(qs[i].replace('\u0001', '"'), qs[i + 2].replace('\u0001', '"'));
}
return map;
}
这些数据
{"name":"John", "age":"30", "car":"a \"quoted\" back\\slash car"}
生成一个包含
{age=30, car=a "quoted" back\slash car, name=John}
这也可以升级为使用未加引号的值…
/**
* A very simple JSON parser for one level, names are quoted.
* @param json the json content.
* @return a key => value map.
*/
public static Map<String, String> simpleParseJson(String json) {
Map<String, String> map = new TreeMap<>();
String qs[] = json.replace("\\\"", "\u0001").replace("\\\\", "\\").split("\"");
for (int i = 1; i + 1 < qs.length; i += 4) {
if (qs[i + 1].trim().length() > 1) {
String x = qs[i + 1].trim();
map.put(qs[i].replace('\u0001', '"'), x.substring(1, x.length() - 1).trim().replace('\u0001', '"'));
i -= 2;
} else {
map.put(qs[i].replace('\u0001', '"'), qs[i + 2].replace('\u0001', '"'));
}
}
return map;
}
为了解决复杂的结构，它变得很难看… ．.． 对不起! !．.． 但我忍不住把它编码了^^ 这将解析给定的JSON以及更多内容。它产生嵌套的映射和列表。
/**
* A very simple JSON parser, names are quoted.
*
* @param json the json content.
* @return a key => value map.
*/
public static Map<String, Object> simpleParseJson(String json) {
Map<String, Object> map = new TreeMap<>();
String qs[] = json.replace("\\\"", "\u0001").replace("\\\\", "\\").split("\"");
int index[] = { 1 };
recurse(index, map, qs);
return map;
}
/**
* Eierlegende Wollmilchsau.
*
* @param index index into array.
* @param map the current map to fill.
* @param qs the data.
*/
private static void recurse(int[] index, Map<String, Object> map, String[] qs) {
int i = index[0];
for (;; i += 4) {
String end = qs[i - 1].trim(); // check for termination of an object
if (end.startsWith("}")) {
qs[i - 1] = end.substring(1).trim();
i -= 4;
break;
}
String key = qs[i].replace('\u0001', '"');
String x = qs[i + 1].trim();
if (x.endsWith("{")) {
x = x.substring(0, x.length() - 1).trim();
if (x.endsWith("[")) {
List<Object> list = new ArrayList<>();
index[0] = i + 2;
for (;;) {
Map<String, Object> inner = new TreeMap<>();
list.add(inner);
recurse(index, inner, qs);
map.put(key, list);
i = index[0];
String y = qs[i + 3]; // check for termination of array
if (y.startsWith("]")) {
qs[i + 3] = y.substring(1).trim();
break;
}
}
continue;
}
Map<String, Object> inner = new TreeMap<>();
index[0] = i + 2;
recurse(index, inner, qs);
map.put(key, inner);
i = index[0];
continue;
}
if (x.length() > 1) { // unquoted
String value = x.substring(1, x.length() - 1).trim().replace('\u0001', '"');
if ("[]".equals(value)) // handle empty array
map.put(key, new ArrayList<>());
else
map.put(key, value);
i -= 2;
} else {
map.put(key, qs[i + 2].replace('\u0001', '"'));
}
}
index[0] = i;
}
yield -如果你打印地图:
{pageInfo={pageName=abc, pagePic=http://example.com/content.jpg}, posts=[{actor_id=1234567890, comments=[], likesCount=2, message=Sounds cool. Can't wait to see it!, nameOfPersonWhoPosted=Jane Doe, picOfPersonWhoPosted=http://example.com/photo.jpg, post_id=123456789012_123456789012, timeOfPost=1234567890}]}
{
"pageInfo": {
"pageName": "abc",
"pagePic": "http://example.com/content.jpg"
},
"posts": [
{
"post_id": "123456789012_123456789012",
"actor_id": "1234567890",
"picOfPersonWhoPosted": "http://example.com/photo.jpg",
"nameOfPersonWhoPosted": "Jane Doe",
"message": "Sounds cool. Can't wait to see it!",
"likesCount": "2",
"comments": [],
"timeOfPost": "1234567890"
}
]
}
Java code :
JSONObject obj = new JSONObject(responsejsonobj);
String pageName = obj.getJSONObject("pageInfo").getString("pageName");
JSONArray arr = obj.getJSONArray("posts");
for (int i = 0; i < arr.length(); i++)
{
String post_id = arr.getJSONObject(i).getString("post_id");
......etc
}
