Skip to main content

Jackson 框架，轻易转换JSON


作者：hoojo
出处： http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html 
blog：http://blog.csdn.net/IBM_hoojo



Jackson 框架，轻易转换JSON
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




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;

/**
 * function: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 hoojo_@126.com
 * @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("hoojo_@126.com");
        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
/**
 * function: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);
    } catch (IOException e) {
        e.printStackTrace();
    }
}
运行后结果如下：
jsonGenerator
{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}
ObjectMapper
{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}
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
/**
 * function: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 map = new HashMap();
        map.put("name", bean.getName());
        map.put("account", bean);
        bean = new AccountBean();
        bean.setAddress("china-Beijin");
        bean.setEmail("hoojo@qq.com");
        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":"hoojo@qq.com"},"name":"hoojo",
"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}}
objectMapper
{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"hoojo@qq.com"},"name":"hoojo",
"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}}
3、 将List集合转换成json
/**
 * function: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 list = new ArrayList();
        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":"hoojo_@126.com"},
{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]
ObjectMapper
1###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"},
{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]
2###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"},
{"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集合
/**
 * function:json字符串转换成list
 * @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> list = objectMapper.readValue(json, List.class);
        System.out.println(list.size());
        for (int i = 0; i < list.size(); i++) {
            Map map = list.get(i);
            Set set = map.keySet();
            for (Iterator 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。
/**
 * function: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
/**
 * function: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> maps = objectMapper.readValue(json, Map.class);
        System.out.println(maps.size());
        Set key = maps.keySet();
        Iterator 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。
/**
 * function: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 list = new ArrayList();
        list.add(bean);
        list.add(bean);
        System.out.println(xml.writeValueAsString(list));
       
        //Map转换xml文档
        Map map = new HashMap();
        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-Guangzhouaddress><name>hoojoname><id>1id><birthday/><email>hoojo_@126.comemail>unknown>
<unknown><unknown><address>china-Guangzhouaddress><name>hoojoname><id>1id><birthday/><email>hoojo_@126.comemail>unknown>
<email><address>china-Guangzhouaddress><name>hoojoname><id>1id><birthday/><email>hoojo_@126.comemail>email>unknown>
<unknown><A><address>china-Guangzhouaddress><name>hoojoname><id>1id><birthday/><email>hoojo_@126.comemail>A>
<B><address>china-Guangzhouaddress><name>hoojoname><id>1id><birthday/><email>hoojo_@126.comemail>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。


Labels:

Comments

Post a Comment

Popular posts from this blog

How to install JSVC on Linux WidenHome Log | WidenHome Log

How to install JSVC on Linux WidenHome Log | WidenHome Log In our team, we have a lot of Java standalone applications which should be run as daemon on Unix/Linux system, and we found JSVC is the best choice for us to wrap Java programs to daemons. This article records the steps on how to install JSVC executable on Linux, which is our stage/prod environment. Download JSVC source package First of all, we need to download JSVC source package from this URL: http://commons.apache.org/daemon/download_daemon.cgi , for example, I downloaded commons-daemon-1.0.5-src.tar.gz file. Or, download it via wget: wget -c http://apache.etoak.com/commons/daemon/source/commons-daemon-1.0.5-src.tar.gz Build JSVC executable Unzip the source package and build JSVC executable. chmod 755 commons-daemon-1.0.5-src.tar.gz tar zxvf commons-daemon-1.0.5-src.tar.gz cd commons-daemon-1.0.5-src/src/native/unix Before building the JSVC executable, please make sure you have set JAVA_HOME variable correctly. And make sur...
4 comments
Read more

Java中的Serializable浅谈

from  http://www.cnblogs.com/vicenteforever/articles/1471775.html 对象的串行化（Serialization） 一、串行化的概念和目的 1.什么是串行化             对象的寿命通常随着生成该对象的程序的终止而终止。有时候，可能需要将对象的状态保存下来，在需要时再将对象恢复。我们把对象的这种能记录自己的状态以便将来再生的能力。叫作对象的持续性(persistence)。对象通过写出描述自己状态的数值来记录自己 ，这个过程叫对象的串行化(Serialization) 。串行化的主要任务是写出对象实例变量的数值。如果交量是另一对象的引用，则引用的对象也要串行化。这个过程是递归的，串行化可能要涉及一个复杂树结构的单行化，包括原有对象、对象的对象、对象的对象的对象等等。对象所有权的层次结构称为图表(graph)。 2.串行化的目的             Java对象的单行化的目标是为Java的运行环境提供一组特性，如下所示： 1)       尽量保持对象串行化的简单扼要 ，但要提供一种途径使其可根据开发者的要求进行扩展或定制。 2)       串行化机制应严格遵守Java的对象模型 。对象的串行化状态中应该存有所有的关于种类的安全特性的信息。 3)       对象的串行化机制应支持Java的对象持续性。 4)       对象的串行化机制应有足够的 可扩展能力以支持对象的远程方法调用(RMI)。 5)       对象串行化应允许对象定义自身 的格式即其自身的数据流表示形式，可外部化接口来完成这项功能。 什么情况下需要序列化 a）当...
Post a Comment
Read more

Log4j Configuration

First, include  Log4j   jar file in your project (e.g. log4j-1.2.8.jar) From  http://www.javabeat.net/tips/82-baisc-steps-to-configure-log4j-using-xml-and.html Configure Log4j This example demonstrated how to configure  Log4j  setup using the Proerties file and  XML file . These are the two most widely used techniques for configuring the  Log4j  for your application. But, in the recent days configuring with  properties files  are considered to be old technique and recommended using  XML . This example program uses simple satndalone java program for running the example. But, in most of the  project  scenarios it will be used in the web application. However the configuration file will be the same. log4j.properties # Set root logger level to DEBUG and its only appender to Appender1. log4j.rootLogger=INFO, Appender1,Appender2 # Appender1 is set to be a ConsoleAppender. log4j.appender.Appender1=org.apache...
Post a Comment
Read more