参考资料：
首先添加maven依赖（版本用最新的）：
<dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-mapper-asl</artifactId> <version>1.9.13</version> </dependency>
然后是POJO对象：
package jackson.pojo;
import java.util.ArrayList;
import java.util.List;
public class User {
private int age = 29;
private String name = "mkyong";
private List<String> messages = new ArrayList<String>() {
private static final long serialVersionUID = 1L;
{
add("msg 1");
add("msg 2");
add("msg 3");
}
};
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<String> getMessages() {
return messages;
}
public void setMessages(List<String> messages) {
this.messages = messages;
}
}
接下来，先测试JAVA对象-->JSON：
package jackson.tojson;
import jackson.pojo.User;
import java.io.File;
import org.codehaus.jackson.map.ObjectMapper;
public class JacksonExample {
public static void main(String[] args) throws Exception {
User user = new User();
ObjectMapper mapper = new ObjectMapper();
// convert user object to json string, and save to a file
mapper.writeValue(new File("e:\\user.json"), user);
// display to console
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user));
}
}
然后测试JSON->JAVA对象：
package jackson.fromjson;
import jackson.pojo.User;
import java.io.File;
import org.codehaus.jackson.map.ObjectMapper;
public class JacksonExample {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
// read from file, convert it to user class
User user = mapper.readValue(new File("e:\\user.json"), User.class);
// display to console
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user));
}
}
JSON->Map:
package jackson.json2map;
import java.util.HashMap;
import java.util.Map;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;
public class JsonMapExample {
public static void main(String[] args) {
String json = "{\"name\":\"mkyong\", \"age\":\"29\"}";
Map<String,String> map = new HashMap<String,String>();
ObjectMapper mapper = new ObjectMapper();
try {
//convert JSON string to Map
map = mapper.readValue(json,
new TypeReference<HashMap<String,String>>(){});
System.out.println(map);
} catch (Exception e) {
e.printStackTrace();
}
}
}
Map->JSON:
package jackson.map2json;
import java.util.HashMap;
import java.util.Map;
import org.codehaus.jackson.map.ObjectMapper;
public class MapJsonExample {
public static void main(String[] args) {
try {
ObjectMapper mapper = new ObjectMapper();
String json = "";
Map<String, String> map = new HashMap<String, String>();
map.put("name", "mkyong");
map.put("age", "29");
//convert map to JSON string
json = mapper.writeValueAsString(map);
System.out.println(json);
} catch (Exception e) {
e.printStackTrace();
}
}
}
Map->JSON File:
package jackson.map2file;
import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.codehaus.jackson.map.ObjectMapper;
public class JsonMapFileExample {
public static void main(String[] args) {
ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = new HashMap<String, Object>();
map.put("name", "mkyong");
map.put("age", 29);
List<Object> list = new ArrayList<Object>();
list.add("msg 1");
list.add("msg 2");
list.add("msg 3");
map.put("messages", list);
try {
// write JSON to a file
mapper.writeValue(new File("e:\\user.json"), map);
} catch (Exception e) {
e.printStackTrace();
}
}
}
JSON FILE->Map:
package jackson.file2map;
import java.io.File;
import java.util.ArrayList;
import java.util.Map;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;
public class JsonFileMapExample {
public static void main(String[] args) {
try {
ObjectMapper mapper = new ObjectMapper();
// read JSON from a file
Map<String, Object> map = mapper.readValue(
new File("e:\\user.json"),
new TypeReference<Map<String, Object>>() {
});
System.out.println(map.get("name"));
System.out.println(map.get("age"));
@SuppressWarnings("unchecked")
ArrayList<String> list = (ArrayList<String>) map.get("messages");
for (String msg : list) {
System.out.println(msg);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
用树的方式操作JSON:
package jackson.treemodel;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.ObjectNode;
public class JacksonTreeNodeExample {
public static void main(String[] args) {
ObjectMapper mapper = new ObjectMapper();
try {
BufferedReader fileReader = new BufferedReader(
new FileReader("e:\\user.json"));
JsonNode rootNode = mapper.readTree(fileReader);
/*** read ***/
JsonNode nameNode = rootNode.path("name");
System.out.println(nameNode.getTextValue());
JsonNode ageNode = rootNode.path("age");
System.out.println(ageNode.getIntValue());
JsonNode msgNode = rootNode.path("messages");
Iterator<JsonNode> ite = msgNode.getElements();
while (ite.hasNext()) {
JsonNode temp = ite.next();
System.out.println(temp.getTextValue());
}
/*** update ***/
((ObjectNode)rootNode).put("nickname", "new nickname");
((ObjectNode)rootNode).put("name", "updated name");
((ObjectNode)rootNode).remove("age");
mapper.writeValue(new File("e:\\user.json"), rootNode);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
用流的方式生成JSON：
package jackson.jsongenerator;
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 = new JsonFactory();
/*** write to file ***/
JsonGenerator jGenerator = jfactory.createJsonGenerator(new File(
"e:\\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();
}
}
}
用流的方式解析JSON：
package jackson.parsejson;
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 = new JsonFactory();
/*** read from file ***/
JsonParser jParser = jfactory.createJsonParser(new File("e:\\user.json"));
// loop until token equal to "}"
while (jParser.nextToken() != JsonToken.END_OBJECT) {
String fieldname = jParser.getCurrentName();
if ("name".equals(fieldname)) {
// current token is "name",
// move to next, which is "name"'s value
jParser.nextToken();
System.out.println(jParser.getText()); // display mkyong
}
if ("age".equals(fieldname)) {
// current token is "age",
// move to next, which is "name"'s value
jParser.nextToken();
System.out.println(jParser.getIntValue()); // display 29
}
if ("messages".equals(fieldname)) {
jParser.nextToken(); // current token is "[", move next
// messages is array, loop until token equal to "]"
while (jParser.nextToken() != 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();
}
}
}