Java 學習記錄87 — Object Input Output including Serialization — 6/7

承 86 — I/O Byte Streams

Location.java

package introduceIo;
import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;
public class Location implements Serializable {
    private final int locationID;
    private final String description;
    private final Map<String, Integer> exits;
    private final static long serialVersionUID = 1L;
    public Location(int locationID, String description, Map<String, Integer> exits) {
        this.locationID = locationID;
        this.description = description;
        if (exits != null) {
            this.exits = new LinkedHashMap<String, Integer>(exits);
        } else {
            this.exits = new LinkedHashMap<String, Integer>();
        }
        this.exits.put("Q", 0);
    }
    public int getLocationID() {
        return locationID;
    }
    public String getDescription() {
        return description;
    }
    public Map<String, Integer> getExits() {
        return new LinkedHashMap<String, Integer>(exits);
    }
    protected void addExit(String direction, int location) {
        exits.put(direction, location);
    }
}

Locations.java

public static void main(String[] args) throws IOException {
//        version 4
        try (ObjectOutputStream locFile = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream("src/introduceIo/locations.dat")))) {
            for (Location location : locations.values()) {
                locFile.writeObject(location);
            }
        }
    }
    
static {
//     read locations.dat
        System.out.println("read locations.dat that combine location and direction in one file");
//        version 2
        try (ObjectInputStream locFile = new ObjectInputStream(new BufferedInputStream(new FileInputStream("src/introduceIo/locations.dat")))) {
            boolean eof = false;
            while (!eof) {
                try {
                    Location location = (Location) locFile.readObject();
                    System.out.println("Read location " + location.getLocationID() + " : " + location.getDescription());
                    System.out.println("Found " + location.getExits().size() + " exits");
                    locations.put(location.getLocationID(), location);
                } catch (EOFException e) {
                    eof = true;
                    System.out.println("EOF exception " + e.getMessage());
                }
            }
        } catch (InvalidClassException e){
            System.out.println("InvalidClassException " + e.getMessage());
        } catch (IOException io) {
            System.out.println("IO exception " + io.getMessage());
        } catch (ClassNotFoundException e) {
            System.out.println("ClassNotFoundException " + e.getMessage());
        } 
 }

做了存讀的序列化

存儲的變得更簡單了

而且讀檔不需要分開讀兩個文件了

合併成一個檔案

如果輸出不順利的話

先把讀檔調回舊的方式，順利讀到後

用新的方式寫入，再用新的方式讀出

private final static long serialVersionUID = 1L;

加上這個可以確保，換到其他電腦也能照這個 UID 來做序列化操作

不加上這個，可能換台電腦時，結果會不同

如果先註銷的話

輸出結果：

InvalidClassException introduceIo.Location; local class incompatible: stream classdesc serialVersionUID = 1, local class serialVersionUID = 351332483920865533

還有要序列化的內容，若是 object 都要是有序的

所以 HashMap 不行，LinkedHashMap 才可以

P.S 但序列化也有個明顯問題，但凡改動文件路徑，就會出錯上面錯誤，要先用舊方式重新寫入

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