jackson将java对象转换为json字符串

来源：互联网发布：lua map数组编辑：程序博客网时间：2024/05/28 15:18

1.1. 下载jackson

Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。相比json-lib框架，Jackson所依赖的jar包较少，简单易用并且性能也要相对高些。而且Jackson社区相对比较活跃，更新速度也比较快。

下载地址: http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.jar

1.2. Java对象转换为json

Person.java

package jackson;

import java.io.Serializable;

public class Person implements Serializable{

/**

private static final long serialVersionUID = 1L;

private Stringname;

private Stringage;

@Override

public String toString() {

return"Person [name=" + name + ", age=" + age + ", sex=" + sex + "]";

}

public Person() {

super();

// TODO Auto-generated constructor stub

}

private Stringsex;

public Person(String name, String age, String sex) {

super();

this.name = name;

this.age = age;

this.sex = sex;

}

public String getName() {

returnname;

}

public void setName(String name) {

this.name = name;

}

public String getAge() {

returnage;

}

public void setAge(String age) {

this.age = age;

}

public String getSex() {

returnsex;

}

public void setSex(String sex) {

this.sex = sex;

}

Java2json.java

package jackson;

import java.io.IOException;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.map.ObjectMapper;

public class Java2Json {

public static void main(String[] args) throws IOException {

ObjectMapper mapper = new ObjectMapper();

JsonGenerator generator = mapper.getJsonFactory().createJsonGenerator(System.out,JsonEncoding.UTF8);

Person person = new Person();

person.setName("morris");

person.setAge("22");

person.setSex("男");

generator.writeObject(person);

System.out.println("----------------");

mapper.writeValue(System.out, person);

}

运行结果如下:

{"sex":"男","age":"22","name":"morris"}----------------

{"sex":"男","age":"22","name":"morris"}

上面分别利用JsonGenerator的writeObject方法和ObjectMapper的writeValue方法完成对Java对象的转换，二者传递的参数及构造的方式不同；JsonGenerator的创建依赖于ObjectMapper对象。也就是说如果你要使用JsonGenerator来转换JSON，那么你必须创建一个ObjectMapper。但是你用ObjectMapper来转换JSON，则不需要JSONGenerator。

1.3. Map集合转换为json

Map2Json.java

package jackson;

import java.io.IOException;

import java.util.HashMap;

import java.util.Map;

import org.codehaus.jackson.map.ObjectMapper;

public class Map2Json {

public static void main(String[] args)throws IOException {

Map<String, String> map = new HashMap<String, String>();

map.put("name", "morris");

map.put("age", "22");

map.put("address", "hk");

ObjectMapper mapper = new ObjectMapper();

String jsonString = mapper.writeValueAsString(map);

System.out.println(jsonString);

}

运行结果如下:

{"address":"hk","age":"22","name":"morris"}

1.4. List集合转换为json

List2json.java

package jackson;

import java.io.IOException;

import java.util.ArrayList;

import java.util.List;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.map.ObjectMapper;

public class List2Json {

public static void main(String[] args)throws IOException {

List<String> list = new ArrayList<String>();

list.add("name");

list.add("age");

list.add("address");

list.add("sex");

ObjectMapper mapper = new ObjectMapper();

JsonGenerator generator = mapper.getJsonFactory().createJsonGenerator(System.out,JsonEncoding.UTF8);

generator.writeObject(list);

System.out.println();

System.out.println("----------------");

//直接将集合转换为json字符串

System.out.println(mapper.writeValueAsString(list));

mapper.writeValue(System.out, list);

}

运行结果如下:

["name","age","address","sex"]

----------------

["name","age","address","sex"]

1.5. 其他对象转换为json

Other2Json.java

package jackson;

import java.io.IOException;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.map.ObjectMapper;

import org.codehaus.jackson.node.JsonNodeFactory;

public class Other2Json {

public static void main(String[] args)throws IOException {

ObjectMapper mapper = new ObjectMapper();

JsonGenerator jsonGenerator = mapper.getJsonFactory().createJsonGenerator(System.out,JsonEncoding.UTF8);

String[] arr = { "a", "b", "c" };

String str = "hello world jackson!";

// byte

jsonGenerator.writeBinary(str.getBytes());

// boolean

jsonGenerator.writeBoolean(true);

// null

jsonGenerator.writeNull();

// float

jsonGenerator.writeNumber(2.2f);

// char

jsonGenerator.writeRaw("c");

// String

jsonGenerator.writeRaw(str, 5, 10);

// String

jsonGenerator.writeRawValue(str, 5, 5);

// String

jsonGenerator.writeString(str);

jsonGenerator.writeTree(JsonNodeFactory.instance.POJONode(str));

System.out.println();

// Object

jsonGenerator.writeStartObject();// {

jsonGenerator.writeObjectFieldStart("user");// user:{

jsonGenerator.writeStringField("name","jackson");// name:jackson

jsonGenerator.writeBooleanField("sex",true);// sex:true

jsonGenerator.writeNumberField("age", 22);// age:22

jsonGenerator.writeEndObject();// }

jsonGenerator.writeArrayFieldStart("infos");//infos:[

jsonGenerator.writeNumber(22);// 22

jsonGenerator.writeString("this is array");// this is array

jsonGenerator.writeEndArray();// ]

jsonGenerator.writeEndObject();// }

Person person = new Person();

person.setAge("22");

person.setName("morris");

person.setSex("男");

// complex Object

jsonGenerator.writeStartObject();// {

jsonGenerator.writeObjectField("user", person);// user:{bean}

jsonGenerator.writeObjectField("infos", arr);//infos:[array]

jsonGenerator.writeEndObject();// }

}

运行结果如下:

"aGVsbG8gd29ybGQgamFja3NvbiE="true null 2.2c world jac worl"hello world jackson!" "hello world jackson!"

{"user":{"name":"jackson","sex":true,"age":22},"infos":[22,"thisis array"]}{"user":{"age":"22","sex":"男","name":"morris"},"infos":["a","b","c"]

1 0