Microsoft PowerPoint - ch7_1 DA class

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1 Quiz 1. Describe the similarities and differences of Tester class and GUI class 2. What is the function of GUI class? 3. What is the function of PD(problem domain) class? 4. How does a GUI class interact with PD class? 1/105 Introduction to Data Access Classes (Reference Chapter 7) 2

2 Topics Make objects persistent ( 持久 ) How to create a DB and data table Design a data access class PD class Communicates with a data access class Use a relational database with Java 3/105 Making Objects Persistent Object persistence The capacity to store and retrieve information from files/database Using it When to store instances or their attributes values for future retrieval 4/105

3 Object Storage Object Storage namely Object serialization ( 序列化 ) To store and retrieve entire instances Advantage The object can be retrieved intact ( 完好无损 ) It is not necessary to re-create the object 5/105 Attribute storage Attribute storage - Involves Writing attribute values to a file or database Retrieving attribute values from a file or database 6/105

4 Files a collection of data or information that has a name, called the filename stored on devices for Long-term storage Magnetic disks Optical disks Magnetic tapes Sequential and random access files 7/105 Data structure in a file File is a group of related records One field in each record is a record key Record key is a unique identifier for a record Sequential file Records stored in order by record key Data hierarchy 8/105

5 Files and data Streams Java views a file as a data stream In a program, we read information from an input stream and write information to an output stream An I/O stream is either a character stream, which deals with text data byte stream, which deal with image and sound data The data is coded using Unicode Unicode : 国际标准字符集 9/105 Buffering Improves performance of I/O Copies each output( 字节或字符 ) to a region of memory called a buffer Entire buffer output to disk at once One long disk access takes less time than many smaller ones ( 成批读入和读出, 高速缓存访问, 效率比较高 ) BufferedOutputStream 类能够在内存里为输出文件建立一个缓冲区 BufferedInputStream buffers file input 10/105

6 Sequential Access File Is a Java File The files Can be byte or text Must start at the beginning and read it sequentially 顺序读写 Can not jump to a specific record number Can not insert or delete a specific record Difficult to update a sequential-access file Entire file must be rewritten to change one field 11/105 Sequential Access File cont. How to read and write Using method readline() in BufferedReader claas Using method println() in PrintStream class java.io.reader java.io.bufferedreader 12/105

7 Random-access access files Access individual records directly and quickly Use fixed length for every record Easy to calculate record locations Insert records without destroying ( 破坏 )other data in file Reads or writes data in spot ( 点 )specified by file-position pointer Manipulates( 操纵 )all data as primitive( 基本 ) types Normally writes one object at a time to file 13/105 Selected Classes in the java.io package File class File 类的方法主要用于获取文件本身的一些信息例如, 文件所在的目录文件的长度等 Constructor File(String filename), 其中参数 filename 是文件名 File(String directorypath, String filename), 其中参数 directorypath 是文件的路径 Methods String getname(): 获取文件的名字 boolean exists(): 判断文件是否存在 long length(): 获取文件的长度 ( 单位是字节 ) boolean isfile(): 判断是否是一个文件 14/105

8 Cont. FileInputStream class( 字节输入流类 ) 可实现以字节为单位顺序读取外存文件的内容到内存,( 用于读取诸如图像数据之类的原始字节流 ) 所用的 method 是 read 关闭字节输入流用的 method 是 close Constructor FileInputStream (String filename), 其中参数 filename 是文件名 ( 包括路径 ) 用给定的文件名创建一个 FileInputStream 实例, 用来打开一个到达该文件的输入流, 这个文件就是源 ( 在外存上 ) FileInputStream (File f), 其中参数 f 是指定的一个文件用来指定要打开那个文件 15/105 Cont. FileOutputStream class( 字节输出流类 ) 用于实现以字节为单位顺序写数据到文件, 所用的方法是 write, 关闭字节输出流使用方法 close 创建 FileOutputStream 类的实例也称为创建文件字节输出流 Constructor FileOutputStream (String filename), 其中参数 filename 是文件名 FileOutputStream (File f), 其中参数 f 是指定的一个文件 16/105

9 Cont. FileReader class( 字符输入流类 ) 用于实现以字符为单位从文件中顺序输入字符流到内存, 使用的方法是 read, 关闭字符输入流使用方法 close Constructor FileReader (String filename) FileReader (File filename) 17/105 Cont. FileWriter class( 字符输出流类 ) 支持以字符为单位顺序的将字符流输出到文件, 使用的方法是 write 方法, 关闭字符输出流用方法 close Constructor FileWriter (String filename) FileWriter (File filename) 18/105

10 Cont. RandomAccessFile class( 随机访问类 ) 支持随机读写文件提供了很多文件的读和写的方法, 例如 : readline, writebytes 等 Constructor RandomAccessFile(String filename,string mode), 其中参数 filename 是文件名, 参数 mode 可能的形式是 r( 只读 ) 或 rw( 可读写 ) RandomAccessFile(File filename,string mode), 其中参数 filename 是文件名, 参数 mode 可能的形式是 r( 只读 ) 或 rw( 可读写 ) 19/105 Create a file and show some info 20/105

11 Read and write to sequence file 21/105 Read and write to Random-access access files RandomAccessFile 类可对文件实现随机读写操作, 即可以随机地读取一个文件中指定位置的记录和写记录到文件指定的位置为方便随机读写, 要求随机文件的每个记录的字节数相等实现随机读写是靠随机文件流的位置指针定位的 RandomAccessFile 对象的文件位置指针遵循下面的规则 : 新建 RandomAccessFile 对象的文件位置指针位于文件的开头处 ; 每次读写操作之后, 文件位置的指针都会相应后移到读写的字节数处 ; 可以通过 getfilepointer 方法来获得位置指针的值, 通过 seek 方法来设置文件指针的位置由此读出指针指向的记录 22/105

12 Example 7.5 将若干个学生的信息存入到文本文件 students.txt 假设要存入的每个学生信息是 : 姓名, 学号, 每一个学生的信息是一个记录然后按规定的顺序读取记录 : 先读第二个学生记录, 再读第一个学生记录, 再读第三个学生记录解题思路 : 先定义问题域 (PD) 类 Student; 然后编写一个主动类 ( 应用程序 ), 能随机读写学生记录 23/105 (1) define Student class Student studentid name 24/105

13 (2) 编写一个能随机读写 3 个学生的记录的程序 TestRandomIO 先创建 3 个 Student 实例, 然后写学生记录到文件 student.txt, 再随机读入注意每个记录的长度应相等, 以便容易确定要读写记录的位置因为一个汉字两个字节, 名字的长度最长是 4 个字, 8 个字节, 学号长度 8 个字节故一个记录共 16 个字节 25/105 (3) TestRandomIO class 26/105

14 cont 27/105 cont 28/105

15 cont 29/105 Databases A database is a collection of data or information that is organized so that it can easily be accessed, managed, and updated. Databases management system (DBMS) Provide tools for organizing data into tables Such as MS SQL server, MS Access, Oracle 30/105

16 In a DBMS Table Relationship Databases Rows, columns Each column represents a field Each row represents a record Primary key: a field used to uniquely identify a record 31/105 Design Databases For example MS Access DB How to create, open and close a Database How to create data tables and close the data table How to modify data table Modify the design of a table add/delete a field How to input and modify data in a table. 32/105

17 Design Databases cont. Implementing the relationship between tables in DB 33/105 JDBC, ODBC, JdbcOdbcDriver Accessing a DBMS with Java, Need JDBC, ODBC and JdbcOdbcDriver JDBC (Java Database Connectivity) 它是一个应用程序接口 (API), 通过它可访问各种关系数据库 JDBC 也是 Java 核心类库的一部分 JDBC 做三件事与数据库建立链接 ; 发送 SQL 语句 ; 处理数据结果 34/105

18 JDBC, ODBC, JdbcOdbcDriver cont. ODBC (Open Database Connectivity in a PC) provided by Microsoft ODBC 是微软公司提出的一套数据库连接标准, 它和 JDBC 优点类似, 主要是为了设置数据库连接接口的统一 ODBC can be used to access most databases (Microsoft SQL Server, Microsoft Access) 35/105 JDBC, ODBC, JdbcOdbcDriver cont. 应用程序要访问一个数据库, 首先用 ODBC 管理器为数据库注册一个数据源名字 (data source name) ODBC 管理器根据数据源提供的数据库位置 ( 路径 ) 数据库类型及 ODBC 驱动程序等信息, 建立起 ODBC 与具体数据库的联系只要应用程序将数据源的名称 (DSN) 提供给 ODBC,ODBC 就能建立起与相应数据库的连接 How to create a DSN(data source name)? 36/105

19 JDBC, ODBC, JdbcOdbcDriver cont. JdbcOdbcDriver: a driver( 驱动程序 ): 要通过 JDBC 访问 ( 存取 ) 某一特定的数据库, 必须有相应的 JDBC driver JDBC (Sun ), ODBC(MS) 不同公司的产品 JDBC --- JdbcOdbcDriver --- ODBC --- DB 37/105 Introduction to SQL Structured Query Language (SQL) A standardized language used to manage and query relational databases ( 在 MS Access 上讲解各语句的执行, 在 Design view 中选 SQL view) 38/105

20 Introduction to SQL cont. Basic SQL statements query and modify tables and columns SELECT Statement - query tables and views in the database INSERT Statement - add rows to tables UPDATE Statement - modify columns in table rows DELETE Statement - remove rows from tables 39/105 SELECT Statement Queries data from tables in the database Basic format SELECT column-list FROM table [WHERE (logical expression )] Example SELECT address, phone FROM customer WHERE name= JoAnn SELECT * FROM customer WHERE name= JoAnn OR name= Mike order by phone SELECT * FROM customer 40/105

21 INSERT Statement Add one row to a table Format INSERT INTO table [(column-list)] VALUES (valuelist) Example INSERT INTO customer VALUES ( Judy, Beijing, ) INSERT INTO customer (name, phone) VALUES ( Judy, ) 41/105 UPDATE Statement Modify columns in selected table rows Format UPDATE table-1 SET set-list [WHERE predicate] SET column-1 = value-1 [, column-2 = value-2]... Example UPDATE customer SET address= Wuhan, phone= WHERE name= Judy 42/105

22 DELETE Statement Removes selected rows from a table Format DELETE FROM table-1 [WHERE predicate] Example DELETE FROM customer WHERE name= Judy 43/105 Selected classes c in java.sql 44/105

23 下面举例说明以上各类的使用编写一个 TestJDBC 程序, 查询数据库 phonebook 中联系人的信息 45/105 TestJDBC class 46/105

24 cont. 47/105 cont. 48/105

25 Data access Application programming model User < > GUI class < >PD class < >DA class< >DB 49/105 Designing a Data Access Class Purpose of a DA class To provide methods that store and retrieve data to files or database Reasons 1. Data input and output code are isolated from other classes Can dramatically reduce maintenance 2. Separate classes for each tier make deployment easier in a client-server environment GUI, PD, and DA functions may reside on multiple machines at various sites 例 : 买卖股票系统 50/105

26 Designing a Data Access Class cont. A separate DA class is written for a PD class ( or one DA class for PD classes) DA methods are invoked only by the PD class A DA class diagram 51/105 Example Define a class User s DA class: UserDA Assume UserDA class attributes userid name password, Methods initialize,terminate,add,update, delete and find 52/105

27 cont Solution Steps: 1. define User class (see P178, 为测试 UserDA 所使用,) 2. [create Database and table usert (see P179, 为测试 UserDA 所使用 ) ] 3. define UserDA class 4. define NotFoundException class (used for UserDA) 5. define DuplicateException class (used for UserDA) 6. Code Tester class 53/105 Designing UserDA class userda class s methods addnew method: public static void add(user auser ) throws DuplicateException { } update method: public static void update(user auser ) throws NotFoundException { } delete method: public static void delete (User auser ) [ throws NotFoundException] { } find method: public static User find (String userid) throws NotFoundException { } 54/105

28 Designing UserDA class class cont. Additional methods Initialize: read data from a file or create a connection to DB public static void initialize(){ } Terminate: write data to a file or close the connection public static void terminate(){ } 55/105 Exception handler classes NotFoundException (used for finding data) public class NotFoundException extends Exception { } DuplicateException (used for add data) public class DuplicateException extends Exception { } 每个方法中的语句根据存储文件类型不同而不同 56/105

29 Implementing DA class with DB add method uses the SQL INSERT INTO statement to add a new user s record to the database update method uses SQL UPDATE statement to change the contents of one or more fields in a user s record 57/105 Implementing DA class with DB cont. Delete method executes the SQL DELETE statement DELETE statement specifies the key value of the customer to be deleted find method uses the SQL SELECT statement to Retrieve a specific user s record from the database 58/105

30 Example: Implementing UserDA class with DB DSN ( 数据源名字 ) 59/105 UserDA class Cont. 60/105

31 UserDA class Cont. 61/105 UserDA class Cont. 62/105

32 UserDA class Cont. 63/105 UserDA class Cont. 64/105

33 UserDA class Cont. 65/105 Defining DuplicateException class public class DuplicateException extends Exception{ //constructor public DuplicateException(String message){ super(message); } } 66/105

34 Defining NotFoundException class public class NotFoundException extends Exception{ //constructor public NotFoundException(String message){ super(message); } } 67/105 Testing interaction of UserDA class and DB Create two User s instance Test each method in UserDA 68/105

35 TesterUserDA class 69/105 cont 70/105

36 cont 71/105 cont 72/105

37 PD Class Communicate with a DA Class 从类图来看两者没有区别 73/105 Modifying PD class:user class User class ( is a PD class) methods in UserDA also includes these methods for invoking initialize Terminate find add update delete static methods instance methods 74/105

38 Modifying PD class:user class Adding methods that invoke UserDA methods 75/105 cont 没有参数代表 user 实例 76/105

39 Testing interaction about User class and UserDA 书中 UserDA change to User 77/105 cont 78/105

40 cont 79/105 较复杂的数据库访问的实现 --- 一对一关系的数据表的访问例 : 现假设要对学生基本信息及住址信息进行管理, 如对这些信息添加修改删除和查询解题思路 : 首先找出问题域类画出类图, 并给出各类的详细说明据此设计相应的数据库表 ; 然后再定义 PD classes 和相应的 DA class; 最后编写测试程序 ( 或定义 GUI 类 ) 80/105

41 (1)) 问题域类图单向关联 81/105 (2)) 创建数据库及数据表 82/105

42 (3)Define PD Class Student class (see P189) 5 attributes (including Address reference) 1 constructor 5 getters, 5 setters? 1 getdetails 3 static methods Initialize, terminate, find 3 instance methods add, update, delete 83/105 (3)Define PD Class cont. Address class (p190) 5 attributes (don t need Student reference?) 1 constructor 5 getters, 5 setters 1getDetails 84/105

43 (4)Define DA Class- StudentDA StudentDA class (p191) 4 attributes 6 methods 85/105 Defined StudentDA class 86/105

44 cont. 87/105 cont. 88/105

45 cont. 89/105 cont. 90/105

46 cont. If need to update the address of the student, how? 91/105 cont. 92/105

47 cont. public Student(String studentid,string name,string phone,string , Address address) { setname( name) ; setstudentid(studentid); setphone( phone); set ( ); setaddress(address); } 通过 Student s constructor 中 setaddress() 完成关联 93/105 P (5)Code Tester class 94/105

48 较复杂的数据库访问的实现 --- 一对多关系的数据表的访问例 : 现假设要查询手机联系人的信息, 包括姓名和电话号码解题思路 : 首先找出问题域类画出类图, 并给出各类的详细说明据此设计相应的数据库表 ; 然后再定义问题域类和相应的数据访问类 ; 最后编写测试程序 95/105 (1)) 问题域类图 96/105

49 (2)) 创建数据库及数据表 97/105 (3)Define PD Class Contact class (session 5.5.3) Phone class 在本例中主要介绍 ContactDA 类中 find 方法和 getall 方法如何编写 Declaring ContactDA class global variables 98/105

50 (4)Define ContactDA Class find method (p179) 控制重复数据只显示一次 99/105 Cont. (4)Define ContactDA Class 建立关联关系 (see p127) 100/105

51 find() 控制流程如下 101/105 (4)Define ContactDA Class getall method 102/105

52 Cont. getall method freqcontact, 103/105 Cont. 104/105

53 getall() 工作流程 : 105/105 Summary Object persistence: storing instance data for future retrieval Persistence can be achieved by storing either attribute values or entire instances A data access (DA) class provides methods that store and retrieve data into tables Methods of a DA class are invoked only by the methods of the corresponding PD class Methods of a DA class: find, addnew, update, delete, getall, initialize, and terminate 106/105

54 Summary Java stream approach to I/O views data input and output as a flow of bytes Persistence can be achieved using sequential files, Random file, object serialization, or relational databases A relational database is used to organize data In a relational database, each column represents a field and each row represents a record SQL is a popular, standard language used to access relational databases 107/105 P200 9,10,11,12,17 第 3 个实验 Practices 108/105

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