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。
class="java">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?monospace; line-height: 1.5; background-color: #fafafa;">NotSerializableException。
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读取反序列化文件:
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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(); } } }
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