java对象实现序列化

今天在看源码的是否发现BaseEntity实现了序列化接口。以前都是模仿别人在实体上实现序列化接口。为了更好的理解序列化的意义，总结java对象序列化。

java对象从内存中写入到磁盘时，经过如下步骤:

(1).声明一个ObjectOutputStream对象，构造ObjectOutputStream对象的时候，传递FileOutputStream对象参数。构造FileOutputStream对象的时候，传递文件或文件路径参数。

(2).构造对象，通过ObjectOutputStream的writeObject方法写入到流中。

import java.util.Date;

public abstract class BaseEntity {
	private String id;
	private Date createTime;
	private Date modifyTime;
	private Date deleteTime;
	private String createUser;
	private String modifyUser;
	private String deleteUser;
	private int deleteFlag = 2;
	private boolean checked = false;
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public Date getCreateTime() {
		return createTime;
	}
	public void setCreateTime(Date createTime) {
		this.createTime = createTime;
	}
	public Date getModifyTime() {
		return modifyTime;
	}
	public void setModifyTime(Date modifyTime) {
		this.modifyTime = modifyTime;
	}
	public Date getDeleteTime() {
		return deleteTime;
	}
	public void setDeleteTime(Date deleteTime) {
		this.deleteTime = deleteTime;
	}
	public String getCreateUser() {
		return createUser;
	}
	public void setCreateUser(String createUser) {
		this.createUser = createUser;
	}
	public String getModifyUser() {
		return modifyUser;
	}
	public void setModifyUser(String modifyUser) {
		this.modifyUser = modifyUser;
	}
	public String getDeleteUser() {
		return deleteUser;
	}
	public void setDeleteUser(String deleteUser) {
		this.deleteUser = deleteUser;
	}
	public int getDeleteFlag() {
		return deleteFlag;
	}
	public void setDeleteFlag(int deleteFlag) {
		this.deleteFlag = deleteFlag;
	}
	public boolean isChecked() {
		return checked;
	}
	public void setChecked(boolean checked) {
		this.checked = checked;
	}
	
	
}
public class Person extends BaseEntity {
	private String name;
	private int age;
	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 "name:"+this.getName()+
			   "age:"+this.getAge()+
			   "checked:"+this.isChecked()+
			   "createTime:"+this.getCreateTime();
	}
	
}

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.Date;

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		//序列化
		Person p1=new Person();
		p1.setAge(1);
		p1.setChecked(true);
		p1.setCreateTime(new Date());
		p1.setName("liming");
		FileOutputStream fos=null;
		ObjectOutputStream oos=null;
		try {
			fos=new FileOutputStream("person1.txt");
			oos=new ObjectOutputStream(fos);
			oos.writeObject(p1);
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally{
			if(oos!=null){
				try {
					oos.close();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			if(fos!=null){
				try {
					fos.close();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}

	}

}

 运行结果为:

java.io.NotSerializableException: net.chinaedu.projects.g3mini.Person

at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)

at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)

at net.chinaedu.projects.g3mini.Test.main(Test.java:27)

从报错结果可以分析出ObjectOutputStream.writeObject方法报错。writeObject方法的源码：

 /**
     * Underlying writeObject/writeUnshared implementation.
     */
    private void writeObject0(Object obj, boolean unshared) 
	throws IOException 
    {
	boolean oldMode = bout.setBlockDataMode(false);
	depth++;
	try {
	    // handle previously written and non-replaceable objects
	    int h;
	    if ((obj = subs.lookup(obj)) == null) {
		writeNull();
		return;
	    } else if (!unshared && (h = handles.lookup(obj)) != -1) {
		writeHandle(h);
		return;
	    } else if (obj instanceof Class) {
		writeClass((Class) obj, unshared);
		return;
	    } else if (obj instanceof ObjectStreamClass) {
		writeClassDesc((ObjectStreamClass) obj, unshared);
		return;
	    }
	    
	    // check for replacement object
	    Object orig = obj;
	    Class cl = obj.getClass();
	    ObjectStreamClass desc;
	    for (;;) {
		// REMIND: skip this check for strings/arrays?
		Class repCl;
		desc = ObjectStreamClass.lookup(cl, true);
		if (!desc.hasWriteReplaceMethod() ||
		    (obj = desc.invokeWriteReplace(obj)) == null ||
		    (repCl = obj.getClass()) == cl)
		{
		    break;
		}
		cl = repCl;
	    }
	    if (enableReplace) {
		Object rep = replaceObject(obj);
		if (rep != obj && rep != null) {
		    cl = rep.getClass();
		    desc = ObjectStreamClass.lookup(cl, true);
		}
		obj = rep;
	    }

	    // if object replaced, run through original checks a second time
	    if (obj != orig) {
		subs.assign(orig, obj);
		if (obj == null) {
		    writeNull();
		    return;
		} else if (!unshared && (h = handles.lookup(obj)) != -1) {
		    writeHandle(h);
		    return;
		} else if (obj instanceof Class) {
		    writeClass((Class) obj, unshared);
		    return;
		} else if (obj instanceof ObjectStreamClass) {
		    writeClassDesc((ObjectStreamClass) obj, unshared);
		    return;
		}
	    }

	    // remaining cases
	    if (obj instanceof String) {
		writeString((String) obj, unshared);
	    } else if (cl.isArray()) {
		writeArray(obj, desc, unshared);
	    } else if (obj instanceof Enum) {
		writeEnum((Enum) obj, desc, unshared);
	    } else if (obj instanceof Serializable) {
		writeOrdinaryObject(obj, desc, unshared);
	    } else {
		if (extendedDebugInfo) {
		    throw new NotSerializableException(
			cl.getName() + "\n" + debugInfoStack.toString());
		} else {
		    throw new NotSerializableException(cl.getName());
		}    
	    }
	} finally {
	    depth--;
	    bout.setBlockDataMode(oldMode);
	}
    }

 其中有一段代码是判断obj类型的，如下

if (obj instanceof String) {
		writeString((String) obj, unshared);
	    } else if (cl.isArray()) {
		writeArray(obj, desc, unshared);
	    } else if (obj instanceof Enum) {
		writeEnum((Enum) obj, desc, unshared);
	    } else if (obj instanceof Serializable) {
		writeOrdinaryObject(obj, desc, unshared);
	    } else {
		if (extendedDebugInfo) {
		    throw new NotSerializableException(
			cl.getName() + "\n" + debugInfoStack.toString());
		} else {
		    throw new NotSerializableException(cl.getName());
		}    
	    }

 先判断obj对象是不是String，Array,Enum，以上都不是的时候，判断是不是对象是不是Serializable的实例。不是的话，写入方法内部会throw NotSerializableException。

 

读取反序列化文件：

 

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.ObjectInputStream;

public class ReadPerson1Test {

	/**
	 * 读取序列化的内容
	 */
	public static void main(String[] args) {
		
		FileInputStream fis=null;
		ObjectInputStream ois=null;
		try {
			fis=new FileInputStream("F:/101edu/svn-work/svn-shiyanban/trunk/dev/src/cedu.g3mini/src/main/java/net/chinaedu/projects/g3mini/person1.txt");
			ois=new ObjectInputStream(fis);
			Person p=(Person) ois.readObject();
			System.err.println(p.toString());
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}

}