本次介绍的是在jackson中,如何去写和解析json,其中用到的都是jackson自己的
流的API.
1 JACKSON中写一个json文件使用的是JsonGenerator类,
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
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