解析Java的Jackson库中对象的序列化与数据泛型绑定

jackson对象序列化
这里将介绍将java对象序列化到一个json文件，然后再读取json文件获取转换为对象。在这个例子中，创建了student类。创建将有学生对象以json表示在一个student.json文件。

创建一个名为jacksontester在java类文件在 c:\>jackson_workspace.

文件: jacksontester.java

import java.io.file;
import java.io.ioexception;

import org.codehaus.jackson.jsongenerationexception;
import org.codehaus.jackson.jsonparseexception;
import org.codehaus.jackson.map.jsonmappingexception;
import org.codehaus.jackson.map.objectmapper;

public class jacksontester {
  public static void main(string args[]){
   jacksontester tester = new jacksontester();
   try {
     student student = new student();
     student.setage(10);
     student.setname("mahesh");
     tester.writejson(student);

     student student1 = tester.readjson();
     system.out.println(student1);

   } catch (jsonparseexception e) {
     e.printstacktrace();
   } catch (jsonmappingexception e) {
     e.printstacktrace();
   } catch (ioexception e) {
     e.printstacktrace();
   }
  }

  private void writejson(student student) throws jsongenerationexception, jsonmappingexception, ioexception{
   objectmapper mapper = new objectmapper(); 
   mapper.writevalue(new file("student.json"), student);
  }

  private student readjson() throws jsonparseexception, jsonmappingexception, ioexception{
   objectmapper mapper = new objectmapper();
   student student = mapper.readvalue(new file("student.json"), student.class);
   return student;
  }
}

class student {
  private string name;
  private int age;
  public student(){}
  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;
  }
  public string tostring(){
   return "student [ name: "+name+", age: "+ age+ " ]";
  } 
}

验证结果

使用 javac 编译如下类：

c:\jackson_workspace>javac jacksontester.java

现在运行jacksontester看到的结果：

c:\jackson_workspace>java jacksontester

验证输出结果

student [ name: mahesh, age: 10 ]

jackson数据绑定泛型
在简单的数据绑定中，我们使用string作为关键对象，并作为一个值对象映射类。相反，我们可以使用具体的java对象和类型强制转换到json使用。

考虑下面的例子使用一个类的userdata来保存用户专用数据。

创建一个名为jacksontester在java类文件目录 c:\>jackson_workspace.

文件名: jacksontester.java

import java.io.file;
import java.io.ioexception;
import java.util.arrays;
import java.util.hashmap;
import java.util.list;
import java.util.map;

import org.codehaus.jackson.jsongenerationexception;
import org.codehaus.jackson.jsonparseexception;
import org.codehaus.jackson.map.jsonmappingexception;
import org.codehaus.jackson.map.objectmapper;
import org.codehaus.jackson.type.typereference;

public class jacksontester {
  public static void main(string args[]){
   jacksontester tester = new jacksontester();
     try {
      objectmapper mapper = new objectmapper();

      map userdatamap = new hashmap();
      userdata studentdata = new userdata(); 
      int[] marks = {1,2,3};

      student student = new student();
      student.setage(10);
      student.setname("mahesh");
      // java object
      studentdata.setstudent(student);
      // java string
      studentdata.setname("mahesh kumar");
      // java boolean
      studentdata.setverified(boolean.false);
      // array
      studentdata.setmarks(marks);
      typereference ref = new typereference>() { };
      userdatamap.put("studentdata1", studentdata);
      mapper.writevalue(new file("student.json"), userdatamap);
      //{
      //  "studentdata1":
      // {
      // "student":
      // {
      //  "name":"mahesh",
      //  "age":10
      //   },
      //   "name":"mahesh kumar",
      //   "verified":false,
      //   "marks":[1,2,3]
      //  }
      //}
      userdatamap = mapper.readvalue(new file("student.json"), ref);

      system.out.println(userdatamap.get("studentdata1").getstudent());
      system.out.println(userdatamap.get("studentdata1").getname());
      system.out.println(userdatamap.get("studentdata1").getverified());
      system.out.println(arrays.tostring(userdatamap.get("studentdata1").getmarks()));
   } catch (jsonparseexception e) {
     e.printstacktrace();
   } catch (jsonmappingexception e) {
     e.printstacktrace();
   } catch (ioexception e) {
      e.printstacktrace();
   }
  }
}

class student {
  private string name;
  private int age;
  public student(){}
  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;
  }
  public string tostring(){
   return "student [ name: "+name+", age: "+ age+ " ]";
  } 
}

class userdata {
  private student student;
  private string name;
  private boolean verified;
  private int[] marks;

  public userdata(){}

  public student getstudent() {
   return student;
  }
  public void setstudent(student student) {
   this.student = student;
  }
  public string getname() {
   return name;
  }
  public void setname(string name) {
   this.name = name;
  }
  public boolean getverified() {
   return verified;
  }
  public void setverified(boolean verified) {
   this.verified = verified;
  }
  public int[] getmarks() {
   return marks;
  }
  public void setmarks(int[] marks) {
   this.marks = marks;
  } 
}

验证输出

使用javac编译如下类：

c:\jackson_workspace>javac jacksontester.java

现在运行jacksontester看到的结果：

c:\jackson_workspace>java jacksontester

验证输出

student [ name: mahesh, age: 10 ]
mahesh kumar
false
[1, 2, 3]