我正在尝试使用杰克逊图书馆解析JSON file text.json的内容。
我想要的是创建一个java方法来获取它的所有键和值，但到目前为止，在我的代码中，我只得到第一个键和JSON文件的第一个值。
我用作制作自己的Java类的指导的代码片段如下：
public void parse(String json) {
JsonFactory factory = new JsonFactory();
ObjectMapper mapper = new ObjectMapper(factory);
JsonNode rootNode = mapper.readTree(json);
Iterator<Map.Entry<String,JsonNode>> fieldsIterator = rootNode.fields();
while (fieldsIterator.hasNext()) {
Map.Entry<String,JsonNode> field = fieldsIterator.next();
System.out.println("Key: " + field.getKey() + "\tValue:" + field.getValue());
}
}
我创建的Java类如下所示：
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
public class JacksonStreamExample {
public static void main(String[] args) {
try {
//Create a JsonFactory instance
JsonFactory factory = new JsonFactory();
//Create a JsonParser instance to read from file c:\\text.json
JsonParser jParser = factory.createJsonParser(new File("c:\\text.json"));
/*Create an ObjectMapper instance to provide a pointer
* to root node of the tree after reading the JSON
*/
ObjectMapper mapper = new ObjectMapper(factory);
//Create tree from JSON
JsonNode rootNode = mapper.readTree(jParser);
Iterator<Map.Entry<String,JsonNode>> fieldsIterator = rootNode.getFields();
while (fieldsIterator.hasNext()) {
Map.Entry<String,JsonNode> field = fieldsIterator.next();
System.out.println("Key: " + field.getKey() + "\tValue:" + field.getValue());
}
jParser.close();
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
我的Eclipse输出如下，只创建一对（键值）：
Key: cells Value:[{"type":"basic.Circle","size":{"width":90,"height":54},"position":{"x":-80,"y":200},"angle":0,"id":"cae4c219-c2cd-4a4b-b50c-0f269963ca24","embeds":"","z":1,"wi_name":"START","wi_displayName":"START","wi_description":"","wi_join":"<None>","wi_split":"<None>","wi_performingRole":"<None>","wi_expected_activity_time":null,"wi_expected_user_time":null,"wi_maximum_activity_time":null,"wi_initial_delay":null,"wi_time_unit":"Seconds","wi_required_transitions_for_AND_JOIN":null,"wi_custom_page":"","attrs":{"circle":{"fill":"#000000","width":50,"height":30,"stroke-width":1,"stroke-dasharray":"0"},"text":{"font-size":10,"text":"START","fill":"#ffffff","font-family":"Arial","stroke":"#000000","stroke-width":0,"font-weight":400}}},{"type":"basic.Circle","size":{"width":90,"height":54},"position":{"x":210,"y":200},"angle":0,"id":"d23133e0-e516-4f72-8127-292545d3d479","embeds":"","z":2,"wi_name":"END","wi_displayName":"END","wi_description":"","wi_join":"<None>","wi_split":"<None>","wi_performingRole":"<None>","wi_expected_activity_time":null,"wi_expected_user_time":null,"wi_maximum_activity_time":null,"wi_initial_delay":null,"wi_time_unit":"Seconds","wi_required_transitions_for_AND_JOIN":null,"wi_custom_page":"","attrs":{"circle":{"fill":"#000000","width":50,"height":30,"stroke-width":1,"stroke-dasharray":"0"},"text":{"font-size":10,"text":"END","fill":"#ffffff","font-family":"Arial","stroke":"#000000","stroke-width":0,"font-weight":400}}},{"type":"basic.Rect","position":{"x":-80,"y":370},"size":{"width":90,"height":54},"angle":0,"id":"a53898a5-c018-45c4-bd3f-4ea4d69f58ed","embeds":"","z":3,"wi_name":"ACTIVITY_1","wi_displayName":"ACTIVITY 1","wi_description":"","wi_join":"<None>","wi_split":"<None>","wi_performingRole":"<None>","wi_expected_activity_time":null,"wi_expected_user_time":null,"wi_maximum_activity_time":null,"wi_initial_delay":null,"wi_time_unit":"Seconds","wi_required_transitions_for_AND_JOIN":null,"wi_custom_page":"","attrs":{"rect":{"width":50,"height":30,"rx":2,"ry":2,"stroke-width":1,"stroke-dasharray":"0"},"text":{"text":"Activity","font-size":10,"font-family":"Arial","stroke":"#000000","stroke-width":0,"font-weight":400}}},{"type":"basic.Rect","position":{"x":220,"y":370},"size":{"width":90,"height":54},"angle":0,"id":"e2bd21f2-508d-44b9-9f68-e374d4fa87ea","embeds":"","z":4,"wi_name":"ACTIVITY_2","wi_displayName":"ACTIVITY 2","wi_description":"","wi_join":"<None>","wi_split":"<None>","wi_performingRole":"<None>","wi_expected_activity_time":null,"wi_expected_user_time":null,"wi_maximum_activity_time":null,"wi_initial_delay":null,"wi_time_unit":"Seconds","wi_required_transitions_for_AND_JOIN":null,"wi_custom_page":"","attrs":{"rect":{"width":50,"height":30,"rx":2,"ry":2,"stroke-width":1,"stroke-dasharray":"0"},"text":{"text":"Workitem","font-size":10,"font-family":"Arial","stroke":"#000000","stroke-width":0,"font-weight":400}}},{"type":"link","source":{"id":"cae4c219-c2cd-4a4b-b50c-0f269963ca24"},"target":{"id":"d23133e0-e516-4f72-8127-292545d3d479"},"router":{"name":"manhattan"},"labels":[{"position":0.5,"attrs":{"text":{"text":"Name"}}}],"id":"60ee7ff7-3a3b-487d-b581-49027e7bebe4","embeds":"","z":5,"attrs":{".marker-source":{"d":"M 10 0 L 0 5 L 10 10 z","transform":"scale(0.001)"},".marker-target":{"d":"M 10 0 L 0 5 L 10 10 z"},".connection":{"stroke":"black"}}},{"type":"link","source":{"id":"a53898a5-c018-45c4-bd3f-4ea4d69f58ed"},"target":{"id":"e2bd21f2-508d-44b9-9f68-e374d4fa87ea"},"router":{"name":"manhattan"},"labels":[{"position":0.5,"attrs":{"text":{"text":"Name"}}}],"id":"cea0d1c2-2c18-4bd7-ba35-d94918c6fc9b","embeds":"","z":6,"attrs":{".marker-source":{"d":"M 10 0 L 0 5 L 10 10 z","transform":"scale(0.001)"},".marker-target":{"d":"M 10 0 L 0 5 L 10 10 z"},".connection":{"stroke":"black"}}}]
我只需要创建一个方法将此代码放入其中以获取所有键值对：
//Create a JsonFactory instance
JsonFactory factory = new JsonFactory();
//Create a JsonParser instance to read from file c:\\text.json
JsonParser jParser = factory.createJsonParser(new File("c:\\text.json"));
/*Create an ObjectMapper instance to provide a pointer
*to root node of the tree after reading the JSON
*/
ObjectMapper mapper = new ObjectMapper(factory);
//Create tree from JSON
JsonNode rootNode = mapper.readTree(jParser);
Iterator<Map.Entry<String,JsonNode>> fieldsIterator = rootNode.getFields();
while (fieldsIterator.hasNext()) {
Map.Entry<String,JsonNode> field = fieldsIterator.next();
System.out.println("Key: " + field.getKey() + "\tValue:" + field.getValue());
}
我该怎么办？
答案 0 :(得分：2)
你应该使用Jackson2而不是Jackson1。正如错误消息指定的那样，Jackson1的JsonNode确实没有fields()方法，而Jackson2's version does。
在Jackson1中，你必须做这样的事情：
Iterator<String> fieldNameIterator = rootNode.getFieldNames();
while (fieldNameIterator.hasNext()) {
String fieldName = fieldNameIterator.next();
JsonNode fieldValue = rootNode.getFieldValue(fieldName);
System.out.println("Key: " + fieldName + "\tValue:" + fieldValue);
}
答案 1 :(得分：1)
现在您已经修改了问题和json，这是您正在寻找的解决方案：
public static void main(String[] args) {
try {
Map source = (new ObjectMapper()).readValue(new File(
"C:\\json.txt"), Map.class);
Map<String, Object> result = new LinkedHashMap<>();
buildFlattenedMap(result, source, null);
for (String s : result.keySet()) {
System.out.println(s);
}
} catch (Exception e) {
e.printStackTrace();
}
}
private static void buildFlattenedMap(Map<String, Object> result,
Map<String, Object> source, String path) {
for (Map.Entry<String, Object> entry : source.entrySet()) {
String key = entry.getKey();
if (hasText(path)) {
if (key.charAt(0) == '[') {
key = StringUtils.join(path, key);
} else {
key = StringUtils.join(path, '.', key);
}
}
Object value = entry.getValue();
if (value instanceof String) {
result.put(key, value);
} else if (value instanceof Map) {
// Need a compound key
@SuppressWarnings("unchecked")
Map<String, Object> map = (Map<String, Object>) value;
buildFlattenedMap(result, map, key);
} else if (value instanceof Collection) {
// Need a compound key
@SuppressWarnings("unchecked")
Collection<Object> collection = (Collection<Object>) value;
int count = 0;
for (Object object : collection) {
buildFlattenedMap(result, Collections.singletonMap("["
+ (count++) + "]", object), key);
}
} else {
result.put(key, value == null ? StringUtils.EMPTY : value);
}
}
}
private static boolean hasText(CharSequence str) {
if (StringUtils.isEmpty(str)) {
return false;
}
int strLen = str.length();
for (int i = 0; i < strLen; i++) {
if (!Character.isWhitespace(str.charAt(i))) {
return true;
}
}
return false;
}
仅供参考，buildFlattenedMap方法实际上来自我最近用于处理类似内容的spring框架。 https://github.com/spring-projects/spring-framework/blob/master/spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java
答案 2 :(得分：1)
我通过更改JSON库解决了我的问题。
我使用了json-simple-1.1.1
我的最终代码如下：
package jsontoxml;
import java.io.*;
import org.json.simple.parser.JSONParser;
import org.json.simple.*;
import java.util.*;
public class JacksonStreamExample {
public static void main(String[] args) {
JSONParser parser = new JSONParser();
try {
Object obj = parser.parse(new FileReader("text.json"));
JSONObject jsonObject = (JSONObject) obj;
JSONArray cells = (JSONArray) jsonObject.get("cells");
Iterator<JSONObject> iterator = cells.iterator();
while(iterator.hasNext()){
System.out.println(iterator.next());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}