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[英]Read Object Array From JSON Array in a JSON file (using Jackson)
[英]Read Json file using Jackson for the following Json structure and Obtain the Object
我能读取一个简单的json文件,它有一个键值对,代码是
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
public class readconfig {
public static void main(String Args[]) throws JsonParseException, JsonMappingException, IOException{
// String inputjson = "{\"key1\":\"value1\", \"key2\":\"value2\", \"key3\":\"value3\"}";
ObjectMapper mapper= new ObjectMapper();
// readjson mp =mapper.readValue(inputjson, readjson.class);
readjson mp =mapper.readValue(new FileInputStream("sam.json"), readjson.class );
System.out.println(mp.getKey1());
}
}
import java.io.*;
import java.io.File;
import java.util.ArrayList;
import java.util.List;
import org.codehaus.jackson.map.ObjectMapper;
public class readjson {
public String k1;
public String k2;
public String k3;
public key1 key;
public key1 getKey() {
return key;
}
public void setKey(key1 key) {
this.key = key;
}
public String getKey1() {
return k1;
}
public void setKey1(String key1) {
this.k1 = key1;
}
public String getKey2() {
return k2;
}
public void setKey2(String key2) {
this.k2 = key2;
}
public String getKey3() {
return k3;
}
public void setKey3(String key3) {
this.k3 = key3;
}
}
问题是我的json文件很复杂这里是我的json文件,它是map的地图,内部map的值是一个列表
{
"key1":
{ "value1":
["listele1",
"listele2"
]
},
"key2":
{ "value2":
["listele1",
"listele2"
]
},
"key3":
{ "value3":
["listele1",
"listele2"
]
}
}
你可以帮助我重新编写列表中内部映射值的值,并反序列化json并将json作为对象
首先,您应该更多地了解Java的命名约定...例如ReadJson
而不是readjson
或String[] args
而不是String Args[]
- 它更方便,更容易阅读。
现在你的问题......请注意你的ReadJson
必须反映与JSON数据相同的结构 - 所以它必须是一个带有字符串键的映射来映射值。 后者再次使用字符串键和字符串值列表。
您可以使用以下代码反序列化:
Map<String, Map<String, List<String>>> readJson = MAPPER.readValue(inputjson, new TypeReference<Map<String, Map<String, List<String>>>>() {});
所以要完整:
public class LearningTest {
public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
String inputJson = "{ \"key1\": { \"value1\": [\"listele1\", \"listele2\" ] }, \"key2\": { \"value2\": [\"listele1\", \"listele2\" ] } }";
Map<String, Map<String, List<String>>> readJson = new ObjectMapper().readValue(inputJson,
new TypeReference<Map<String, Map<String, List<String>>>>() {
});
System.out.println(readJson.get("key1").get("value1").get(0));
}
}
如您所见,此方法不再需要专用数据类(ReadJson.java)。
如果您希望将所有列表元素放在一个列表中,则可以这样:
List<String> elements = readJson.values() // Collection<Map<String, List<String>>>
.stream() // Stream<Map<String, List<String>>>
.flatMap(value -> value.values().stream()) // Stream<List<String>>
.flatMap(listOfStrings -> listOfStrings.stream()) // Stream<String>
.collect(Collectors.toList()); // List<String>
System.out.println(elements);
或者您可以访问以下单个列表:
List<String> listOfFirstInnerMap = readJson.get("key1").get("value1");
List<String> listOfSecondInnerMap = readJson.get("key2").get("value2");
您的json映射到此Java对象:
Map<String, Map<String, String[]>>
以下是一些可以构建的代码:
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;
public class TestJson {
public static void main(String[] args) throws Exception {
Map<String, Map<String, String[]>> myFile = new HashMap<>();
Map<String, String[]> subMap1 = new HashMap<>();
Map<String, String[]> subMap2 = new HashMap<>();
Map<String, String[]> subMap3 = new HashMap<>();
String[] myArray = new String[] {"listele1", "listele2"};
subMap1.put("value1", myArray);
subMap2.put("value2", myArray);
subMap3.put("value3", myArray);
myFile.put("key1", subMap1);
myFile.put("key2", subMap2);
myFile.put("key3", subMap3);
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(myFile));
}
}
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