Java Read Object Input Stream Into Arraylist
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1- ObjectInputStream
ObjectInputStream- это подкласс класса InputStream, который управляет объектом InputStream и предоставляет методы для чтения примитивных данных (primitive data) или объекта из InputStream, которым он управляет.
public class ObjectInputStream extends InputStream implements ObjectInput, ObjectStreamConstants
ObjectInputStream используется для чтения источников данных, записанных ObjectOutputStream.
ObjectInputStream methods
public boolean readBoolean() throws IOException public byte readByte() throws IOException public int readUnsignedByte() throws IOException public char readChar() throws IOException public short readShort() throws IOException public int readUnsignedShort() throws IOException public int readInt() throws IOException public long readLong() throws IOException public float readFloat() throws IOException public double readDouble() throws IOException public void readFully(byte[] buf) throws IOException public void readFully(byte[] buf, int off, int len) throws IOException public int skipBytes(int len) throws IOException public String readUTF() throws IOException public last ObjectInputFilter getObjectInputFilter() public final void setObjectInputFilter(ObjectInputFilter filter) public final Object readObject() throws IOException, ClassNotFoundException public Object readUnshared() throws IOException, ClassNotFoundException public void defaultReadObject() throws IOException, ClassNotFoundException public ObjectInputStream.GetField readFields() throws IOException, ClassNotFoundException public void registerValidation(ObjectInputValidation obj, int prio) throws NotActiveException, InvalidObjectException protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, ClassNotFoundException protected Object readObjectOverride() throws IOException, ClassNotFoundException protected Class<?> resolveProxyClass(String[] interfaces) throws IOException, ClassNotFoundException protected Object resolveObject(Object obj) throws IOException protected boolean enableResolveObject(boolean enable) throws SecurityException protected void readStreamHeader() throws IOException, StreamCorruptedException protected ObjectStreamClass readClassDescriptor() throws IOException, ClassNotFoundException String readTypeString() throws IOException // Methods inherited from InputStream: public int read() throws IOException public int read(byte[] buf, int off, int len) throws IOException public int available() throws IOException public void shut() throws IOException
ObjectInputStream constructors
public ObjectInputStream(InputStream in)
ii- Example i
В этом примере мы запишем объекты Employee в файл, а затем будем использовать ObjectInputStream для чтения файла.
Класс Employee должен реализовать (implement) интерфейс Serializable , это необходимо для того, чтобы его можно было записать в ObjectOutputStream.
Employee.java
package org.o7planning.beans; import java.io.Serializable; public class Employee implements Serializable { individual static last long serialVersionUID = 1L; private String fullName; private float salary; public Employee(String fullName, bladder salary) { this.fullName = fullName; this.salary = salary; } public String getFullName() { render fullName; } public void setFullName(String firstName) { this.fullName = firstName; } public float getSalary() { return salary; } public void setSalary(float lastName) { this.salary = lastName; } }
Затем используем ObjectOutputStream для записи объектов Employee в файл.
WriteEmployeeDataEx.java
package org.o7planning.objectinputstream.ex; import coffee.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectOutputStream; import java.io.OutputStream; import java.util.Date; import org.o7planning.beans.Employee; public class WriteEmployeeDataEx { // Windows: C:/Data/examination/employees.data individual static String file_path = "/Volumes/Data/test/employees.data"; public static void primary(String[] args) throws IOException { File outFile = new File(file_path); outFile.getParentFile().mkdirs(); Employee e1 = new Employee("Tom", 1000f); Employee e2 = new Employee("Jerry", 2000f); Employee e3 = new Employee("Donald", 1200f); Employee[] employees = new Employee[] { e1, e2, e3 }; OutputStream os = new FileOutputStream(outFile); ObjectOutputStream oos = new ObjectOutputStream(os); Organisation.out.println("Writing file: " + outFile.getAbsolutePath()); oos.writeObject(new Date()); oos.writeUTF("Employee information"); // Some informations. oos.writeInt(employees.length); // Number of Employees for (Employee e : employees) { oos.writeObject(e); } oos.shut(); System.out.println("Finished!"); } }
После запуска класса WriteEmployeeDataEx мы получаем файл с запутанным содержимым
Наконец, используем ObjectInputStream для чтения файла, только что записанного на предыдущем шаге.
ReadEmployeeDataEx.java
package org.o7planning.objectinputstream.ex; import java.io.File; import coffee.io.FileInputStream; import coffee.io.IOException; import java.io.InputStream; import java.io.ObjectInputStream; import java.util.Date; import org.o7planning.beans.Employee; public course ReadEmployeeDataEx { // Windows: C:/Data/test/employees.data private static String file_path = "/Volumes/Information/exam/employees.information"; public static void chief(String[] args) throws IOException, ClassNotFoundException { File inFile = new File(file_path); InputStream is = new FileInputStream(inFile); ObjectInputStream ois = new ObjectInputStream(is); Organisation.out.println("Reading file: " + inFile.getAbsolutePath()); System.out.println(); Appointment date = (Appointment) ois.readObject(); Cord info = ois.readUTF(); System.out.println(date); System.out.println(info); System.out.println(); int employeeCount = ois.readInt(); for(int i=0; i< employeeCount; i++) { Employee due east = (Employee) ois.readObject(); System.out.println("Employee Name: " + e.getFullName() +" / Salary: " + east.getSalary()); } ois.close(); } }
Output:
Reading file: /Volumes/Data/test/employees.data Sat Mar 20 18:54:24 KGT 2021 Employee data Employee Proper noun: Tom / Salary: g.0 Employee Proper name: Jerry / Salary: 2000.0 Employee Name: Donald / Salary: 1200.0
3- readFields()
Предположим, вы используете ObjectInputStream для чтения объекта GameSetting из файла. В то же время, читая объект GameSetting, вы хотите изменить значения некоторых его полей (field).
GameSetting.coffee
package org.o7planning.beans; import java.io.IOException; import coffee.io.ObjectInputStream; public class GameSetting implements java.io.Serializable { private static final long serialVersionUID = 1L; private int audio; private int bightness; individual String difficultyLevel; private Cord userNote; public GameSetting(int sound, int bightness, Cord difficultyLevel, String userNote) { this.sound = audio; this.bightness = bightness; this.difficultyLevel = difficultyLevel; this.userNote = userNote; } public int getSound() { render sound; } public int getBightness() { render bightness; } public String getDifficultyLevel() { render difficultyLevel; } public Cord getUserNote() { return userNote; } // Do not change proper name and parameter of this method. private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ObjectInputStream.GetField fields = in.readFields(); this.sound = fields.become("sound", 50); this.bightness = fields.get("bightness", 50); // Edit fields this.difficultyLevel = (String) fields.get("difficultyLevel", "Easy"); // Default if (this.difficultyLevel == zero) { this.difficultyLevel = "Easy"; } this.userNote = (String) fields.get("userNote", "Accept fun!"); // Default if (this.userNote == null) { this.userNote = "Have fun!"; } } }
ObjectInputStream_readFields.java
parcel org.o7planning.objectinputstream.ex; import java.io.File; import coffee.io.FileInputStream; import coffee.io.FileOutputStream; import coffee.io.IOException; import java.io.InputStream; import java.io.ObjectInputStream; import coffee.io.ObjectOutputStream; import java.io.OutputStream; import java.util.Appointment; import org.o7planning.beans.GameSetting; public form ObjectInputStream_readFields { // Windows: C:/Information/test/game_setting.data individual static String file_path = "/Volumes/Data/test/game_setting.data"; public static void principal(String[] args) throws IOException, ClassNotFoundException { GameSetting setting = new GameSetting(10, 80, null, nil); writeGameSetting(setting); readGameSetting(); } individual static void writeGameSetting(GameSetting setting) throws IOException { File file = new File(file_path); file.getParentFile().mkdirs(); OutputStream os = new FileOutputStream(file); ObjectOutputStream oos = new ObjectOutputStream(os); // Write a Cord oos.writeUTF("Game Settings, Salvage at " + new Appointment()); // Write Object oos.writeObject(setting); oos.close(); } private static void readGameSetting() throws IOException, ClassNotFoundException { File file = new File(file_path); file.getParentFile().mkdirs(); InputStream is = new FileInputStream(file); ObjectInputStream ois = new ObjectInputStream(is); // Read a String String info = ois.readUTF(); // Read fields GameSetting setting = (GameSetting) ois.readObject(); Organization.out.println("sound: " + setting.getSound()); System.out.println("bightness: " + setting.getBightness()); System.out.println("difficultyLevel: " + setting.getDifficultyLevel()); Organization.out.println("userNote: " + setting.getUserNote()); // cypher. ois.close(); } }
Output:
sound: 10 bightness: eighty difficultyLevel: Easy userNote: Have fun!
iv- readUnshared()
Метод ObjectInputStream.readUnshared() используется для чтения объекта, записанного методом ObjectOutputStream.writeUnshared(Object).
ObjectInputStream_readUnshared.java
packet org.o7planning.objectinputstream.ex; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import coffee.io.ObjectInputStream; import java.io.ObjectOutputStream; import coffee.io.OutputStream; import java.util.ArrayList; public grade ObjectInputStream_readUnshared { // Windows: C:/Data/test/test1.data private static String file_path = "/Volumes/Data/test/test.data"; public static void main(Cord[] args) throws IOException, ClassNotFoundException { writeUnsharedTest(); readUnsharedTest(); } private static void writeUnsharedTest() throws IOException { File file = new File(file_path); file.getParentFile().mkdirs(); ArrayList<String> list = new ArrayList<String>(); list.add("I"); listing.add("Two"); OutputStream os = new FileOutputStream(file); ObjectOutputStream oos = new ObjectOutputStream(os); oos.writeUnshared(listing); // Write the first time oos.writeUnshared(listing); // Write the second time oos.close(); } @SuppressWarnings({ "unchecked" }) private static void readUnsharedTest() throws IOException, ClassNotFoundException { File file = new File(file_path); ArrayList<String> listing = new ArrayList<String>(); list.add("One"); listing.add("Two"); InputStream is = new FileInputStream(file); ObjectInputStream ois = new ObjectInputStream(is); ArrayList<String> list1 = (ArrayList<String>) ois.readUnshared(); ArrayList<String> list2 = (ArrayList<String>) ois.readUnshared(); System.out.println("list1 == list2? " + (list1 == list2)); ois.close(); } }
Output:
См.Объяснение метода ObjectOutputStream.writeUnshared(Object):
Source: https://betacode.net/13397/java-objectinputstream
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