Jackson框架:Java对象与json、xml格式的数据之间的转换

  在Java项目中將一个对象转换成一段Json格式的字符串是非常常见的，能够实现这种需求的工具包也比较多，例如Gson、JSON-lib、Jackson等等。本文主要介绍Jackson的使用，Jackson除了能实现Java对象与Json串的互转外，还能將Java对象转换为Xml格式，使用较为简单而且据说效率比较高。
对于Jackson的jar包我们可以从maven资源库中下载：http://mvnrepository.com/
所需要的jar包：

前面有介绍过json-lib这个框架，在线博文：http://www.cnblogs.com/hoojo/archive/2011/04/21/2023805.html
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。
一、准备工作
 1.下载依赖库jar包(jackson-all-1.6.2.jar)
  然后在工程中导入这个jar包即可开始工作
  官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes
 如果你需要转换xml，那么还需要stax2-api.jar
 2.测试类基本代码如下:

package cn.keymobile;import java.io.IOException;import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.List;import java.util.Map;import java.util.Set;import org.junit.After;import org.junit.Before;import org.junit.Test;import com.fasterxml.jackson.core.JsonEncoding;import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.core.JsonGenerator;import com.fasterxml.jackson.core.JsonParseException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.node.JsonNodeFactory;import com.fasterxml.jackson.dataformat.xml.XmlMapper;/** * 将Java对象转换成json字符串，也可以将json字符串转换成Java对象 * @author zhaojd * */public class JacksonTest {    private JsonGenerator jsonGenerator = null;    private ObjectMapper objectMapper = null;    private AccountBean bean = null;    @SuppressWarnings("deprecation")    @Before    public void init() {        bean = new AccountBean();        bean.setAddress("china-Guangzhou");        bean.setEmail("[e-mail]");        bean.setId(1);        bean.setName("zhaojd");        objectMapper = new ObjectMapper();        try {            jsonGenerator =                    objectMapper.getJsonFactory()                            .createJsonGenerator(System.out, JsonEncoding.UTF8);        } catch (IOException e) {            e.printStackTrace();        }    }    @After    public void destory() {        try {            if (jsonGenerator != null) {                jsonGenerator.flush();            }            if (!jsonGenerator.isClosed()) {                jsonGenerator.close();            }            jsonGenerator = null;            objectMapper = null;            bean = null;            System.gc();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 1.1 java对象转换成json      */    @Test    public void javaBeanToJson() throws Exception {        try {            System.out.println("jsonGenerator");            /**             * writeObject()可以转换Java对象；例如：JavaBean/Map/List/Array等             */            jsonGenerator.writeObject(bean);            System.out.println();            System.out.println("ObjectMapper");            /**             * writeValue() 和 writeObject() 是相同的功能             */            objectMapper.writeValue(System.out, bean);        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 所谓的json格式：     *     {"键":"值","键":"值","键":"值"}     * jsonGenerator     *  {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null}     *  ObjectMapper     *  {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null}     */    /**     * 1.2 将Map集合转换成json字符串     * @throws Exception     */    @Test    public void mapToJson() throws Exception {        try {            Map<String, Object> map = new HashMap<String, Object>();            map.put("name", bean.getName());            map.put("account", bean);            bean = new AccountBean();            bean.setAddress("china-Lanzhou");            bean.setEmail("[e-mail]");            map.put("account2", bean);            System.out.println("jsonGenerator");            jsonGenerator.writeObject(map);            System.out.println("");            System.out.println("objectMapper");            objectMapper.writeValue(System.out, map);        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * jsonGenerator     *  {     *   "account2":{"address":"china-Lanzhou","name":null,"id":0,"email":"[e-mail]","birthday":null},     *   "name":"zhaojd",     *   "account":{"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null}     *  }     *  objectMapper     *  {     *   "account2":{"address":"china-Lanzhou","name":null,"id":0,"email":"[e-mail]","birthday":null},     *   "name":"zhaojd","     *   account":{"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null}     *  }     */    /**     * 1.3 将List转换成json     */    @Test    public void listToJson() throws Exception {        try {            List<AccountBean> list = new ArrayList<AccountBean>();            list.add(bean);            bean = new AccountBean();            bean.setId(2);            bean.setAddress("address2");            bean.setEmail("email2");            bean.setName("name2");            list.add(bean);            System.out.println("jsonGenerator");            jsonGenerator.writeObject(list);            System.out.println();            System.out.println("ObjectMapper");            /**             * 用objectMapper直接返回list转换成的JSON字符串             */            System.out.println("直接返回list转换成的json" + objectMapper.writeValueAsString(list));            //objectMapper list转换成JSON字符串            objectMapper.writeValue(System.out, list);        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * jsonGenerator     *  [     *      {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null},     *      {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}     *  ]     *  ObjectMapper     *  直接返回list转换成的json[     *      {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null},     *      {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}     *  ]     *  [     *      {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[e-mail]","birthday":null},     *      {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}     *  ]     */    /**     * 1.4 下面来看看jackson提供的一些类型，用这些类型完成json转换；如果你使用这些类型转换JSON的话，     *     那么你即使没有JavaBean(Entity)也可以完成复杂的Java类型的JSON转换。     *     下面用到这些类型构建一个复杂的Java对象，并完成JSON转换。     */    @Test    public void othersToJson() throws Exception {        try {            String[] arr = {"a", "b", "c"};            System.out.println("jsonGenerator");            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();//}            AccountBean bean = new AccountBean();            bean.setAddress("address");            bean.setEmail("email");            bean.setId(1);            bean.setName("haha");            //complex Object            jsonGenerator.writeStartObject();//{            jsonGenerator.writeObjectField("user", bean);//user:{bean}            jsonGenerator.writeObjectField("infos", arr);//infos:[array]            jsonGenerator.writeEndObject();//}        } catch (Exception e) {            e.printStackTrace();        }    }    /**     * jsonGenerator     *  "aGVsbG8gd29ybGQgamFja3NvbiE=" true null 2.2c world jac  worl "hello world jackson!" "hello world jackson!"     *   {"user":{"name":"jackson","sex":true,"age":22},"infos":[22,"this is array"]}      *   {"user":{"address":"address","name":"haha","id":1,"email":"email","birthday":null},"infos":["a","b","c"]}     */    /**     * 2.1 将json字符串转换成JavaBean对象     */    @Test    public void jsonToJavaBean() throws Exception {        String json = "{\"name\":\"zhaojd\",\"email\":\"email\",\"address\":\"address\"}";        try {            AccountBean acc = objectMapper.readValue(json, AccountBean.class);            System.out.println(acc.getName());            System.out.println(acc);        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * zhaojd     * 0#zhaojd#email#address#null     */    /**     * 2.2 将json 转换成List     */    @SuppressWarnings("unchecked")    @Test    public void jsonToList() {        String json =                "[{\"address\": \"address2\",\"name\":\"zhaojd\",\"id\":2,\"email\":\"email2\"},"                        + "{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}]";        try {            List<LinkedHashMap<String, Object>> list = objectMapper.readValue(json, List.class);            System.out.println("list的长度:" + list.size());            for (int i = 0; i < list.size(); i++) {                Map<String, Object> map = list.get(i);                Set<String> set = map.keySet();                for (Iterator<String> it = set.iterator(); it.hasNext();) {                    String key = it.next();                    System.out.println(key + ":" + map.get(key));                }            }        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     *   list的长度：2     *   address:address2     *   name:zhaojd     *   id:2     *   email:email2     *   address:address     *   name:zhaojd     *   id:1     *   email:email     */    /**     * 2.3 json字符串转换成Array     */    @Test    public void jsonToArray() throws Exception {        String json =                "[{\"address\": \"address2\",\"name\":\"zhaojd2\",\"id\":2,\"email\":\"email2\"},"                        + "{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}]";        try {            AccountBean[] arr = objectMapper.readValue(json, AccountBean[].class);            System.out.println("数组的长度为：" + arr.length);            for (int i = 0; i < arr.length; i++) {                System.out.println(arr[i]);            }        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     *   数组的长度为：2     *   2#zhaojd2#email2#address2#null     *   1#zhaojd#email#address#null     */    /**     * 2.4 json转换成Map集合     */    @SuppressWarnings("unchecked")    @Test    public void jsonToMap() throws Exception {        String json =                "{\"success\":true,\"A\":{\"address\": \"address2\",\"name\":\"zhaojd2\",\"id\":2,\"email\":\"email2\"},"                        + "\"B\":{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}}";        try {            Map<String, Map<String, Object>> maps = objectMapper.readValue(json, Map.class);            System.out.println("map集合的长度为：" + maps.size());            Set<String> key = maps.keySet();            Iterator<String> iter = key.iterator();            while (iter.hasNext()) {                String field = iter.next();                System.out.println(field + ":" + maps.get(field));            }        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    /*     *   map集合的长度为：3     *   success:true     *   A:{address=address2, name=zhaojd2, id=2, email=email2}     *   B:{address=address, name=zhaojd, id=1, email=email}     */    /**     * 3. jackson对xml的支持     */    @Test    public void objectToXml() throws Exception {        System.out.println("XmlMapper");        XmlMapper xml = new XmlMapper();        try {            /**             * javaBean转换成xml             */            AccountBean account = new AccountBean();            Birthday birthday = new Birthday("1992-08");            account.setAddress("广州");            account.setBirthday(birthday);            account.setEmail("mr_zhaojd");            account.setId(1);            account.setName("zhaojd");            String xmlStr = xml.writeValueAsString(account);            System.out.println(xmlStr);            /**             * List转换成xml             */            List<AccountBean> list = new ArrayList<AccountBean>();            list.add(account);            list.add(account);            System.out.println(xml.writeValueAsString(list));            /**             * Map转换xml文档             */            Map<String, AccountBean> map = new HashMap<String, AccountBean>();            map.put("A", account);            map.put("B", account);            System.out.println(xml.writeValueAsString(map));        } catch (JsonGenerationException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * XmlMapper        <AccountBean xmlns="">            <id>1</id>            <name>zhaojd</name>            <email>mr_zhaojd</email>            <address>广州</address>            <birthday><birthday>1992-08</birthday></birthday>        </AccountBean>        <ArrayList xmlns="">            <id>1</id>            <name>zhaojd</name>            <email>mr_zhaojd</email>            <address>广州</address>            <birthday><birthday>1992-08</birthday></birthday>         </ArrayList>         <zdef532234490:ArrayList xmlns:zdef532234490="">             <zdef532234490:id>1</zdef532234490:id>             <zdef532234490:name>zhaojd</zdef532234490:name>             <zdef532234490:email>mr_zhaojd</zdef532234490:email>             <zdef532234490:address>广州</zdef532234490:address>             <zdef532234490:birthday><zdef532234490:birthday>1992-08</zdef532234490:birthday></zdef532234490:birthday>         </zdef532234490:ArrayList>        <HashMap xmlns="">            <A>                <id>1</id>                <name>zhaojd</name>                <email>mr_zhaojd</email>                <address>广州</address>                <birthday><birthday>1992-08</birthday></birthday>            </A>            <B>                <id>1</id>                <name>zhaojd</name>                <email>mr_zhaojd</email>                <address>广州</address>                <birthday><birthday>1992-08</birthday></birthday>            </B>        </HashMap>     */    @Test    public void xmlToObject() {        XmlMapper xmlMapper = new XmlMapper();        String xml = "<AccountBean><id>1</id><name>zhaojd</name><email>mr_zhaojd</email><address>广州</address><birthday><birthday>1992-08</birthday></birthday></AccountBean>";        try {            AccountBean ab = xmlMapper.readValue(xml,AccountBean.class);            System.out.println(ab);        }  catch (IOException e) {            e.printStackTrace();        }    }    /**     * 1#zhaojd#mr_zhaojd#广州#1992-08     */}

参考原文出处：
http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html
http://blog.csdn.net/Rongbo_J/article/details/47986121