ObjectMapper JSON的处理

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本文介绍如何使用Jackson库进行高效的JSON处理，包括将Java对象转换为JSON字符串或将JSON字符串转换回Java对象的方法。通过示例展示了不同类型的Java数据结构与JSON之间的相互转换。

Jackson 高性能的JSON处理 android/移动开发必备jackson

分类： android 2011-11-08 20:10 469人阅读评论(0) 收藏举报

今天自行研究了下json ，感觉非常好用，经过测试比google的GSON快多了

同时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。功能非常的强悍！

大家也知道，json 在如今互联网时代应用的非常广，因为大家如此的关注，所以对json的解析性能要求也是非常高的。

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

[java] view plain copy

/
@project java
@package
@file Jackson.java
@version 1.0
@author 廖益平
@time 2011-11-8 上午02:59:37
/
public class Jackson {
/
Class Descripton goes here.
@class Jackson
@version 1.0
@author 廖益平
@time 2011-11-8 上午02:59:37
/
public static JsonGenerator jsonGenerator = null;
private static ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) {
Student student = new Student();
student.setIsstudent(true);
student.setUid(1000);
student.setUname(”xiao liao”);
student.setUpwd(”123”);
student.setNumber(12);
Map<String, Student> stuMap = new HashMap<String, Student>();
stuMap.put(”1”, student);
stuMap.put(”2”, student);
List<Object> stuList = new ArrayList<Object>();
List<Student> stuList1 = new ArrayList<Student>();
stuList1.add(student);
student= new Student();
student.setIsstudent(false);
student.setUid(200);
student.setUname(”xiao mi”);
stuList1.add(student);
stuList.add(student);
stuList.add(”xiao xin”);
stuList.add(”xiao er”);
stuList.add(stuMap);
//readJson2List();
try {
//readJson2Array();
//writeArray2Json(array);
//writeJson2List();
//writeEntity2Json(student);
writeJson2Entity();
//writeMap2Json(stuMap);
//writeList2Json(stuList1);
} catch (IOException e) {
e.printStackTrace();
}
}
/
<code>writeEntity2Json</code>
@description: TODO(实体类转换成json)
@param object
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeEntity2Json(Object object) throws IOException {
mapper.writeValue( new File(“D:\developSoft\aaadowload\testjson1\lib\aa.txt”),object );
mapper.writeValue( System.out,object );
}
/
<code>writeArray2Json</code>
@description: TODO(数组转换成json数组)
@param object
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeArray2Json(Object object) throws IOException {
// writeValue具有和writeObject相同的功能
mapper.writeValue( new File(“D:\developSoft\aaadowload\testjson1\lib\aa.txt”),object );
mapper.writeValue(System.out,object );
}
/
<code>writeMap2Json</code>
@description: TODO(map对象转换成json对象)
@param object
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeMap2Json(Object object) throws IOException {
System.out.println(”使用ObjectMapper———–”);
// writeValue具有和writeObject相同的功能
System.out.println(”==>”+mapper.writeValueAsString(object));
mapper.writeValue( new File(“D:\developSoft\aaadowload\testjson1\lib\aamap.txt”),object );
mapper.writeValue( System.out , object );
}
/
<code>writeList2Json</code>
@description: TODO(list转换成json)
@param object
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeList2Json(Object object) throws IOException {
System.out.println(”==>”+mapper.writeValueAsString(object));
mapper.writeValue( new File(“D:\developSoft\aaadowload\testjson1\lib\aamap.txt”),object );
mapper.writeValue( System.out , object );
}
/
<code>writeJson2Entity</code>
@description: TODO(json转换成实体)
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeJson2Entity() throws IOException {
System.out.println(”json串转换成entity————-“);
// File file = new File(“D:\developSoft\aaadowload\testjson1\lib\aa.txt”);
// FileInputStream inputStream = new FileInputStream(file);
// Student student = mapper.readValue(inputStream,Student.class);
// System.out.println(student.toString());
//漂亮输出
//mapper.defaultPrettyPrintingWriter().writeValueAsString(value);
String json = ”{\”uid\”:1000,\”uname\”:\”xiao liao\”,\”upwd\”:\”123\”,\”number\”:12.0,\”isstudent\”:true}”;
Student student1 = mapper.readValue(json,Student.class);
System.out.println(”json2:”+student1.toString());
}
/
<code>writeJson2List</code>
@description: TODO(json专程list对象)
@throws IOException
@since 2011-11-8 廖益平
/
public static void writeJson2List() throws IOException {
System.out.println(”json串转换成entity————-“);
File file = new File(“D:\developSoft\aaadowload\testjson1\lib\aa.txt”);
FileInputStream inputStream = new FileInputStream(file);
Student student = mapper.readValue(inputStream,Student.class);
System.out.println(student.toString());
String json = ”[{\”uid\”:1000,\”uname\”:\”xiao liao\”,\”upwd\”:\”123\”,\”number\”:12.0,\”isstudent\”:true},{\”uid\”:200,\”uname\”:\”xiao mi\”,\”upwd\”:null,\”number\”:0.0,\”isstudent\”:false}]”;
List<LinkedHashMap<String, Object>> s= mapper.readValue(json,List.class);
for (int i = 0; i < s.size(); i++) {
LinkedHashMap<String, Object> link = s.get(i);
Set<String> key = link.keySet();
for (Iterator iterator = key.iterator(); iterator.hasNext();) {
String string = (String) iterator.next();
System.out.println(string+”==>”+link.get(string));
}
System.out.println(”json:”+i+“”+s.get(i).toString());
}
}
/
JSON转换为List对象
/
public static void readJson2List() {
String json = ”[{\”uid\”:1,\”uname\”:\”www\”,\”number\”:234,\”upwd\”:\”456\”},”
+ ”{\”uid\”:5,\”uname\”:\”tom\”,\”number\”:3.44,\”upwd\”:\”123\”}]”;
try {
List<LinkedHashMap<String, Object>> list = mapper.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();
}
}
/
JSON转换为List对象
*/
public static void readJson2Array() {
String json = ”[{\”uid\”:1,\”uname\”:\”www\”,\”number\”:234,\”upwd\”:\”456\”},”
+ ”{\”uid\”:5,\”uname\”:\”tom\”,\”number\”:3.44,\”upwd\”:\”123\”}]”;
try {
Student[] students = mapper.readValue(json, Student[].class);
for (Student student : students) {
System.out.println(”>”+student.toString());
}
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

打印结果：

串转换成entity————-
json2:uid=1000,name=xiao liao,upwd=123,number=12.0,isStudent=true

writeMap2Json ———–
{“2”:{“uid”:1000,”uname”:”xiao liao”,”upwd”:”123”,”number”:12.0,”isstudent”:true},”1”:{“uid”:1000,”uname”:”xiao liao”,”upwd”:”123”,”number”:12.0,”isstudent”:true}}

readJson2Array——————
>uid=1,name=www,upwd=456,number=234.0,isStudent=false
>uid=5,name=tom,upwd=123,number=3.44,isStudent=false
writeMap2Json ———–
{“2”:{“uid”:1000,”uname”:”xiao liao”,”upwd”:”123”,”number”:12.0,”isstudent”:true},”1”:{“uid”:1000,”uname”:”xiao liao”,”upwd”:”123”,”number”:12.0,”isstudent”:true}}

大家逐个自己试试吧，上面也是我的测试代码

[java] view plain copy

实体类：
/
@project java
@package
@file Student.java
@version 1.0
@author 廖益平
@time 2011-11-8 上午03:01:08
/
public class Student {
/
Class Descripton goes here.
@class Student
@version 1.0
@author 廖益平
@time 2011-11-8 上午03:01:08
*/
private int uid;
private String uname;
private String upwd;
private double number;
private boolean isstudent;
public int getUid() {
return uid;
}
public void setUid(int uid) {
this.uid = uid;
}
public String getUname() {
return uname;
}
public void setUname(String uname) {
this.uname = uname;
}
public String getUpwd() {
return upwd;
}
public void setUpwd(String upwd) {
this.upwd = upwd;
}
public double getNumber() {
return number;
}
public void setNumber(double number) {
this.number = number;
}
public boolean isIsstudent() {
return isstudent;
}
public void setIsstudent(boolean isstudent) {
this.isstudent = isstudent;
}
@Override
public String toString() {
return “uid=”+uid+“,name=”+uname+“,upwd=”+upwd+“,number=”+number+“,isStudent=”+isstudent;
}
}