关于java:JAVA基础之序列化

明天来讲讲序列化以及反序列化

Serializable 接口，没有 method，实现该接口表明能够序列化以及反序列化
ObjectOutputStream，将 Object 序列化为 stream 流
ObjectInputStream，通过 stream 流反序列化转化为 Object
序列化时，计算出一个 Serial version unique identifier 标识这个 class（平安的哈希值），并将这个哈希值其存储到 stream 中，而反序列化时 java 再次计算这个 class 的标识值（如果 class 类的定义已扭转则值也会发生变化），新计算的值与从 stream 取出来的值做比拟，如果不统一，示意该类的序列化版本与咱们领有的以后类定义不兼容。会产生 InvalidClassException。

public class BankAccount implements Serializable {
    private String id;
    private int balance = 0;
    public BankAccount(String id){this.id = id;}
    public BankAccount(String id, int startBalance){
        this.id = id;
        balance = startBalance;
    }
    public String getId(){return id;}
    public synchronized int getBalance(){return balance;}
    public synchronized void deposit(int amount){balance += amount;}
    public synchronized void withdrawal(int amount){balance -= amount;}
}

序列化与反序列化办法

public class Main {public static void main(String[] args) {BankAccount ba = new BankAccount("10",500);
        ba.deposit(250);
        saveAccount(ba,"/Users/buxuesong/Documents/svn_code/demo/account.dat");
        BankAccount bb = loadAccount("/Users/buxuesong/Documents/svn_code/demo/account.dat");
        System.out.println(bb.getId() +"|" + bb.getBalance());
    }
    private static void saveAccount(BankAccount ba, String fileName){try(ObjectOutputStream os = new ObjectOutputStream(Files.newOutputStream(Paths.get(fileName)))){os.writeObject(ba);
        }catch(Exception e){System.out.println(e.getSuppressed() +"|"+ e.getMessage());
        }
    }
    private static BankAccount loadAccount(String fileName){
        BankAccount ba = null;
        try(ObjectInputStream oi = new ObjectInputStream(Files.newInputStream(Paths.get(fileName)))){ba = (BankAccount) oi.readObject();}catch(Exception e){System.out.println(e.getSuppressed() +"|"+ e.getMessage());
        }
        return ba;
    }
}
输入
10 | 750

当扭转了 class 的定义字段后，与原有序列化的惟一标识不同，导致无奈反序列化，这就须要自定义 serialVersionUID，当前批改了该类，也会能够反序列化回来，只是新增的字段默认值为空或者是原始默认值（int 的话就是 0）

private static final long serialVersionUID = -23324324324L;

还能够自定义序列化以及反序列化的办法，在 BankAccount 中

private void writeObject(ObjectOutputStream out) throws IOException {out.defaultWriteObject();
}

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException{ObjectInputStream.GetField fields = in.readFields();
    id = (String) fields.get("id",null);
    balance = fields.get("balance",0);
    lastTxType = fields.get("lastTxType",'u');
    lastTxAmount = fields.get("lastTxAmount",-1);
}

执行办法

BankAccount bb = loadAccount("/Users/buxuesong/Documents/svn_code/demo/account.dat");
System.out.println(bb.getId() +"|" + bb.getBalance()+"|" +bb.getLastTxType()+"|"+bb.getLastTxAmount());
输入
10 | 750 | u | -1

还能够针对某些字段不必须做序列化解决，须要通过 transient 润饰该字段，能够通过其它形式获取回来，这样节俭了序列化的工夫
具体如下

public class AccountGroup implements Serializable {
    private static final long serialVersionUID = 106962907155393149L;

    private Map<String, BankAccount> accountMap = new HashMap();
    private transient int totalBalance;
    public int getTotalBalance(){return totalBalance;}
    public void addAccount(BankAccount account){totalBalance += account.getBalance();
        accountMap.put(account.getId(), account);
    }
    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {in.defaultReadObject();
        for(BankAccount account: accountMap.values())
            totalBalance += account.getBalance();}
}

执行办法中的存储到流以及从流中取回的办法

private static void saveGroup(AccountGroup g, String fileName){try(ObjectOutputStream os = new ObjectOutputStream(Files.newOutputStream(Paths.get(fileName)))){os.writeObject(g);
    }catch(Exception e){System.out.println(e.getSuppressed() +"|"+ e.getMessage());
    }
}

private static AccountGroup loadGroup(String fileName){
    AccountGroup g = null;
    try(ObjectInputStream oi = new ObjectInputStream(Files.newInputStream(Paths.get(fileName)))){g = (AccountGroup) oi.readObject();}catch(Exception e){System.out.println(e.getSuppressed() +"|"+ e.getMessage());
    }
    return g;
}

执行办法：

BankAccount acct1 = new BankAccount("1234", 500);
BankAccount acct2 = new BankAccount("9866", 750);
AccountGroup group = new AccountGroup();
group.addAccount(acct1);
group.addAccount(acct2);
saveGroup(group, "/Users/buxuesong/Documents/svn_code/demo/group.dat");
AccountGroup group2 = loadGroup("/Users/buxuesong/Documents/svn_code/demo/group.dat");
System.out.println("group2.getTotalBalance:"+group2.getTotalBalance());

输入

group2.getTotalBalance:1250

其余序列化办法，实现 Externalizable 接口

void writeExternal(ObjectOutput out);
void readExternal(ObjectInput in);