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objectmapper类是jackson库的主要类。它提供一些功能将转换成java对象匹配json结构，反之亦然。它使用jsonparser和jsongenerator的实例实现json实际的读/写。
类声明
以下是org.codehaus.jackson.map.objectmapper类的声明：
public class objectmapper extends objectcodec implements versioned
嵌套类
| s.n. | 类 & 描述 |
|---|---|
| 1 | static class objectmapper.defaulttyperesolverbuilder//定制typeresolverbuilder，提供所谓的“默认输入”使用类型解析构建器（见enabledefaulttyping()了解详细信息）。 |
| 2 | static class objectmapper.defaulttyping//使用enabledefaulttyping()枚举指定什么样的类型（类）默认输入应该使用。 |
| s.n. | 构造函数 & 描述 |
|---|---|
| 1 | objectmapper()//默认的构造函数，这将构建默认jsonfactory必要时使用stdserializerprovider作为其serializerprovider，并beanserializerfactory作为其serializerfactory。 |
| 2 | objectmapper(jsonfactory jf)//构造使用指定的jsonfactory构建必要的jsonparsers和/或jsongenerators映射。 |
| 3 | objectmapper(jsonfactory jf, serializerprovider sp, deserializerprovider dp) |
| 4 | objectmapper(jsonfactory jf, serializerprovider sp, deserializerprovider dp, serializationconfig sconfig, deserializationconfig dconfig) |
| 5 | objectmapper(serializerfactory sf) 不推荐使用。使用其他构造来代替; 注意，可以设置序列化工厂setserializerfactory（org.codehaus.jackson.map.serializerfactory） |
例子
测试类基本代码如下
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/*
* @project java
* @package
* @file jackson.java
* @version 1.0
*/
public class jackson {
/*
*
* class descripton goes here.
*
* @class jackson
* @version 1.0
*/
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
*/
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
*/
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
*/
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
*/
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
*/
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
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