java Jackson框架学习

将字符串转化成实体集合

List<SQZCOrderDtail> list= om.readValue(node.findPath("result"),new TypeReference<List<SQZCOrderDtail>>(){});//把json转换为list<实体> 

Jackson是一个采用Java开发的高性能JSON处理器（JSON解析器+JSON生成器）。它比其它任何Java JSON Parser和Data Binder都快。除了基本的JSON读写功能之外，它提供完全基于节点的Tree Model和完整的OJM (Object/Json Mapper)数据绑定功能，可以绑定任意Java Bean、Collection、Map或Enum。
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。

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

因为下面的程序是用junit测试用例运行的，所以还得添加junit的jar包。版本是junit-4.2.8

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

自己写的例子：

import java.io.IOException;
import java.io.StringWriter;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;



import net.sf.json.JSONArray;

import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.ObjectMapper;



public class JacksonTest {

	@SuppressWarnings("all")
	private JsonGenerator jsonGenerator = null;  
    private ObjectMapper objectMapper = null; 
    private StringWriter strw = null ;  
    //初始化一些基本信息
    public JacksonTest()
    {
    	objectMapper = new ObjectMapper();  
    	strw = new StringWriter() ;
    	try {  
            jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(strw); 
            //设置日期格式  
    		SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
    		objectMapper.setDateFormat(fmt);  
    		objectMapper.enableDefaultTyping();
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }
    private String formateObject(Object value)
    {
    	String json = "";
		try {
	     json = objectMapper.writeValueAsString(value);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return json;
    }
    private String formateListObject(Object value)
    {
		try {
	     objectMapper.writeValue(strw, value);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return strw.toString();
    }
    @SuppressWarnings("all")
    private Object parseJsonString(String jsonValue,Class clazz)
    {
    	Object result = null ;
		try {
			result = objectMapper.readValue(jsonValue,clazz);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return result;
    }
    
    @SuppressWarnings("all")
	public static void main(String[] args) throws Exception{
		 JacksonTest jacksonTest = new JacksonTest();
		 Person person = new Person("lwx",23,"1234",new Date());
		 Person person2 = new Person("lwx",24,"1234",new Date());
		 List<Person> pList = new ArrayList<Person>() ;
		 pList.add(person);
		 pList.add(person2);
         System.out.println(jacksonTest.formateObject(person));
         System.out.println(jacksonTest. formateListObject(pList));
         JSONArray array1 = JSONArray.fromObject(jacksonTest. formateListObject(pListStr)); 
         //Json 转 List
         for(int i = 0; i < array1.size(); i++) {
        	JSONArray array2 = JSONArray.fromObject(array1.getString(i));  
        	System.out.println(jacksonTest.parseJsonString(array2.getString(1), Person.class));
         }  
	}
};

class Person{
	private String name ;
	
	private int age ;
	private String id ;
	
	private Date date ;
	//无参构造器是必须有的  json转对象时无参构造函数必须要有
	public Person() {  
	} 
	
	
	public Person(String name, int age, String id, Date date) {
		super();
		this.name = name;
		this.age = age;
		this.id = id;
		this.date = date;
	}


	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public Date getDate() {
		return date;
	}
	public void setDate(Date date) {
		this.date = date;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString()
	{
		return "姓名："+this.name+" 年龄："+this.age+" 日期："+this.date;
	}
};

package com.hoo.test;
 
import java.io.IOException;
import java.io.StringWriter;
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.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.JsonNodeFactory;
import org.codehaus.jackson.xml.XmlMapper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.hoo.entity.AccountBean;
 
/**
 * <b>function:</b>Jackson 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
 * jar-lib-version: jackson-all-1.6.2
 * jettison-1.0.1
 * @author hoojo
 * @createDate 2010-11-23 下午04:54:53
 * @file JacksonTest.java
 * @package com.hoo.test
 * @project Spring3
 * @blog http://blog.csdn.net/IBM_hoojo
 * @email [e-mail]
 * @version 1.0
 */
@SuppressWarnings("unchecked")
public class JacksonTest {
    private JsonGenerator jsonGenerator = null;
    private ObjectMapper objectMapper = null;
    private AccountBean bean = null;
    
    @Before
    public void init() {
        bean = new AccountBean();
        bean.setAddress("china-Guangzhou");
        bean.setEmail("[e-mail]");
        bean.setId(1);
        bean.setName("hoojo");
        
        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();
        }
    }
}

3、 所需要的JavaEntity

package com.hoo.entity;
 
public class AccountBean {
    private int id;
    private String name;
    private String email;
    private String address;
    private Birthday birthday;
    
    //getter、setter
    
    @Override
    public String toString() {
        return this.name + "#" + this.id + "#" + this.address + "#" + this.birthday + "#" + this.email;
    }
}
Birthday

package com.hoo.entity;
 
public class Birthday {
    private String birthday;
    
    public Birthday(String birthday) {
        super();
        this.birthday = birthday;
    }
 
    //getter、setter
 
    public Birthday() {}
    
    @Override
    public String toString() {
        return this.birthday;
    }
}

二、Java对象转换成JSON

1、 JavaBean(Entity/Model)转换成JSON

/**
 * <b>function:</b>将java对象转换成json字符串
 * @author hoojo
 * @createDate 2010-11-23 下午06:01:10
 */
@Test
public void writeEntityJSON() {
    
    try {
        System.out.println("jsonGenerator");
        //writeObject可以转换java对象，eg:JavaBean/Map/List/Array等
        jsonGenerator.writeObject(bean);    
        System.out.println();
        
        System.out.println("ObjectMapper");
        //writeValue具有和writeObject相同的功能
        objectMapper.writeValue(System.out, bean);
        //StringWriter strw = new StringWriter();
        //jsonGenerator=objectMapper.getJsonFactory().createJsonGenerator(strw);
        //objectMapper.writeValue(strw, bean);  这样就不json内容写到StringWriter中
        //String jsonStr = strw.toString();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
/*运行后结果如下：
jsonGenerator
{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"}
ObjectMapper
{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"}
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。

objectMapper的writeValue方法可以将一个Java对象转换成JSON。这个方法的参数一，需要提供一个输出流，转换后可以通过这个流来输出转换后的内容。或是提供一个File，将转换后的内容写入到File中。当然，这个参数也可以接收一个JSONGenerator，然后通过JSONGenerator来输出转换后的信息。第二个参数是将要被转换的Java对象。如果用三个参数的方法，那么是一个Config。这个config可以提供一些转换时的规则，过指定的Java对象的某些属性进行过滤或转换等。
*/

2、 将Map集合转换成Json字符串

/**
 * <b>function:</b>将map转换成json字符串
 * @author hoojo
 * @createDate 2010-11-23 下午06:05:26
 */
@Test
public void writeMapJSON() {
    try {
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("name", bean.getName());
        map.put("account", bean);
        bean = new AccountBean();
        bean.setAddress("china-Beijin");
        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();
    }
}
转换后结果如下：

jsonGenerator
{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"[e-mail]"},"name":"hoojo",
"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"}}
objectMapper
{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"[e-mail]"},"name":"hoojo",
"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"}}

3、 将List集合转换成json

/**
 * <b>function:</b>将list集合转换成json字符串
 * @author hoojo
 * @createDate 2010-11-23 下午06:05:59
 */
@Test
public void writeListJSON() {
    try {
        List<AccountBean> list = new ArrayList<AccountBean>();
        list.add(bean);
        
        bean = new AccountBean();
        bean.setId(2);
        bean.setAddress("address2");
        bean.setEmail("email2");
        bean.setName("haha2");
        list.add(bean);
        
        System.out.println("jsonGenerator");
        //list转换成JSON字符串
        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("1###" + objectMapper.writeValueAsString(list));
        System.out.print("2###");
        //objectMapper list转换成JSON字符串
        objectMapper.writeValue(System.out, list);
    } catch (IOException e) {
        e.printStackTrace();
    }
}
结果如下：

jsonGenerator
[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"},
{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]
ObjectMapper
1###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"},
{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]
2###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[e-mail]"},
{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]
外面就是多了个[]中括号；同样Array也可以转换，转换的JSON和上面的结果是一样的，这里就不再转换了。~.~

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 writeOthersJSON() {
    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();
    }
}
运行后，结果如下：

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,"birthday":null,"email":"email"},"infos":["a","b","c"]}
怎么样？构造的json字符串和输出的结果是一致的吧。关键看懂用JSONGenerator提供的方法，完成一个Object的构建。

三、JSON转换成Java对象

1、 将json字符串转换成JavaBean对象

@Test
public void readJson2Entity() {
    String json = "{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}";
    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();
    }
}
很简单，用到了ObjectMapper这个对象的readValue这个方法，这个方法需要提供2个参数。第一个参数就是解析的JSON字符串，第二个参数是即将将这个JSON解析吃什么Java对象，Java对象的类型。当然，还有其他相同签名方法，如果你有兴趣可以一一尝试使用方法，当然使用的方法和当前使用的方法大同小异。运行后，结果如下：

haha
haha#1#address#null#email

2、 将json字符串转换成List<Map>集合

/**
 * <b>function:</b>json字符串转换成list<map>
 * @author hoojo
 * @createDate 2010-11-23 下午06:12:01
 */
@Test
public void readJson2List() {
    String json = "[{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
                "{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";
    try {
        List<LinkedHashMap<String, Object>> list = objectMapper.readValue(json, List.class);
        System.out.println(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();
    }
}
尝试过将上面的JSON转换成List，然后List中存放AccountBean，但结果失败了。但是支持Map集合。因为你转成List.class，但是不知道List存放何种类型。只好默然Map类型。因为所有的对象都可以转换成Map结合，运行后结果如下：

2
address:address2
name:haha2
id:2
email:email2
address:address
name:haha
id:1
email:email

3、 Json字符串转换成Array数组，由于上面的泛型转换不能识别到集合中的对象类型。所有这里用对象数组，可以解决这个问题。只不过它不再是集合，而是一个数组。当然这个不重要，你可以用Arrays.asList将其转换成List即可。

/**
 * <b>function:</b>json字符串转换成Array
 * @author hoojo
 * @createDate 2010-11-23 下午06:14:01
 */
@Test
public void readJson2Array() {
    String json = "[{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
            "{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";
    try {
        AccountBean[] arr = objectMapper.readValue(json, AccountBean[].class);
        System.out.println(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();
    }
}
运行后的结果：

2
haha2#2#address2#null#email2
haha#1#address#null#email

4、 Json字符串转换成Map集合

/**
 * <b>function:</b>json字符串转换Map集合
 * @author hoojo
 * @createDate Nov 27, 2010 3:00:06 PM
 */
@Test
public void readJson2Map() {
    String json = "{\"success\":true,\"A\":{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
                "\"B\":{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}}";
    try {
        Map<String, Map<String, Object>> maps = objectMapper.readValue(json, Map.class);
        System.out.println(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();
    }
}
运行后结果如下：

3
success:true
A:{address=address2, name=haha2, id=2, email=email2}
B:{address=address, name=haha, id=1, email=email}

四、Jackson对XML的支持

Jackson也可以完成java对象到xml的转换，转换后的结果要比json-lib更直观，不过它依赖于stax2-api.jar这个jar包。

/**
 * <b>function:</b>java对象转换成xml文档
 * 需要额外的jar包 stax2-api.jar
 * @author hoojo
 * @createDate 2010-11-23 下午06:11:21
 */
@Test
public void writeObject2Xml() {
    //stax2-api-3.0.2.jar
    System.out.println("XmlMapper");
    XmlMapper xml = new XmlMapper();
    
    try {
        //javaBean转换成xml
        //xml.writeValue(System.out, bean);
        StringWriter sw = new StringWriter();
        xml.writeValue(sw, bean);
        System.out.println(sw.toString());
        //List转换成xml
        List<AccountBean> list = new ArrayList<AccountBean>();
        list.add(bean);
        list.add(bean);
        System.out.println(xml.writeValueAsString(list));
        
        //Map转换xml文档
        Map<String, AccountBean> map = new HashMap<String, AccountBean>();
        map.put("A", bean);
        map.put("B", bean);
        System.out.println(xml.writeValueAsString(map));
    } catch (JsonGenerationException e) {
        e.printStackTrace();
    } catch (JsonMappingException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
运行上面的方法，结果如下：

XmlMapper
<unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[e-mail]</email></unknown>
<unknown><unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[e-mail]</email></unknown>
<email><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[e-mail]</email></email></unknown>
<unknown><A><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[e-mail]</email></A>
<B><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[e-mail]</email></B></unknown>
看结果，根节点都是unknown 这个问题还没有解决，由于根节点没有转换出来，所有导致解析xml到Java对象，也无法完成。

所用的jar包 看附件。
转载请注明出处 本文出自：[url]http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html [/url]