jackson中的写和解析JSON的api例子


import java.io.File;
import java.io.IOException;
import org.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.map.JsonMappingException;

public class JacksonStreamExample {
public static void main(String[] args) {

try {

JsonFactory jfactory &＃61; new JsonFactory();

/*** write to file ***/
JsonGenerator jGenerator &＃61; jfactory.createJsonGenerator(new File(
"c:\\user.json"), JsonEncoding.UTF8);
jGenerator.writeStartObject(); // {

jGenerator.writeStringField("name", "mkyong"); // "name" : "mkyong"
jGenerator.writeNumberField("age", 29); // "age" : 29

jGenerator.writeFieldName("messages"); // "messages" :
jGenerator.writeStartArray(); // [

jGenerator.writeString("msg 1"); // "msg 1"
jGenerator.writeString("msg 2"); // "msg 2"
jGenerator.writeString("msg 3"); // "msg 3"

jGenerator.writeEndArray(); // ]

jGenerator.writeEndObject(); // }

jGenerator.close();

} catch (JsonGenerationException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

}


输出为:

{

"name":"mkyong",

"age":29,

"messages":["msg 1","msg 2","msg 3"]

}

2 解析JSON

我们把上面输出的JSON文件重新读取出来,再解析, 注意在json中,解析是以TOKEN方式进行的,比如:

{

"name":"mkyong"

}

将为解析为:

Token 1 &＃61; “{“

Token 2 &＃61; “name”

Token 3 &＃61; “mkyong”

Token 4 &＃61; “}”



代码:


import java.io.File;
import java.io.IOException;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonToken;
import org.codehaus.jackson.map.JsonMappingException;

public class JacksonStreamExample {
public static void main(String[] args) {

try {

JsonFactory jfactory &＃61; new JsonFactory();

/*** read from file ***/
JsonParser jParser &＃61; jfactory.createJsonParser(new File("c:\\user.json"));

// loop until token equal to "}"
while (jParser.nextToken() !&＃61; JsonToken.END_OBJECT) {

String fieldname &＃61; jParser.getCurrentName();
if ("name".equals(fieldname)) {


//当前结点为name
jParser.nextToken();
System.out.println(jParser.getText()); // 输出 mkyong

}

if ("age".equals(fieldname)) {

// 当前结点为age
// move to next, which is "name"&＃39;s value
jParser.nextToken();
System.out.println(jParser.getIntValue()); // display 29

}

if ("messages".equals(fieldname)) {

jParser.nextToken();
while (jParser.nextToken() !&＃61; JsonToken.END_ARRAY) {

// display msg1, msg2, msg3
System.out.println(jParser.getText());

}

}

}
jParser.close();

} catch (JsonGenerationException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

}


最后输出:

mkyong

29

msg 1

msg 2

msg 3