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## 5. 基于Spring框架的后端应用开发
### 5.1 Java基础增强
#### 5.1.1 Java异常处理
**练习任务**:
1. **异常处理练习**:
- 创建一个方法，该方法接受两个整数参数，并返回它们的除法结果。如果第二个参数为0，则抛出自定义异常。
- 在主程序中调用该方法，并使用try-catch块来捕获异常，输出友好的错误信息。
- 示例代码:
```java
public class Division {
public static double divide(int a, int b) throws IllegalArgumentException {
if (b == 0) {
throw new IllegalArgumentException("除数不能为0");
}
return (double) a / b;
}
public static void main(String[] args) {
try {
double result = divide(10, 0);
System.out.println("结果: " + result);
} catch (IllegalArgumentException e) {
System.out.println(e.getMessage());
}
}
}
```
2. **自定义异常练习**:
- 创建一个自定义异常类`InvalidAgeException`，继承自`IllegalArgumentException`。
- 创建一个方法`validateAge`，接收一个年龄参数，如果年龄小于0或大于150，则抛出`InvalidAgeException`。
- 在主程序中调用`validateAge`方法，并捕获异常，输出异常信息。
- 示例代码:
```java
public class AgeValidator {
public static void validateAge(int age) throws InvalidAgeException {
if (age < 0 || age > 150) {
throw new InvalidAgeException("年龄无效");
}
}
public static void main(String[] args) {
try {
validateAge(-5);
} catch (InvalidAgeException e) {
System.out.println(e.getMessage());
}
}
}
class InvalidAgeException extends IllegalArgumentException {
public InvalidAgeException(String message) {
super(message);
}
}
```
#### 5.1.2 注解
**练习任务**:
1. **自定义注解练习**:
- 创建一个自定义注解`@MyAnnotation`，并带有字符串属性`value`。
- 创建一个类`AnnotatedClass`，并在其方法上使用`@MyAnnotation`注解。
- 编写一个程序读取该注解，并打印出注解的值。
- 示例代码:
```java
import java.lang.reflect.Method;
public @interface MyAnnotation {
String value();
}
public class AnnotatedClass {
@MyAnnotation(value = "Hello, Annotation!")
public void myMethod() {
// 方法实现
}
public static void main(String[] args) {
Method[] methods = AnnotatedClass.class.getDeclaredMethods();
for (Method method : methods) {
MyAnnotation annotation = method.getAnnotation(MyAnnotation.class);
if (annotation != null) {
System.out.println(annotation.value());
}
}
}
}
```
#### 5.1.3 Optional的介绍和使用
**练习任务**:
1. **Optional练习**:
- 创建一个方法`getUserById`，该方法接收一个ID参数，并返回一个`Optional<User>`对象。
- 如果ID对应的数据存在，则返回包含用户对象的`Optional`；否则返回空的`Optional`。
- 在主程序中调用该方法，并使用`ifPresent`或`orElse`方法处理结果。
- 示例代码:
```java
public class User {
private String name;
public User(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
public class UserService {
public static Optional<User> getUserById(long id) {
if (id == 1) {
return Optional.of(new User("John Doe"));
} else {
return Optional.empty();
}
}
public static void main(String[] args) {
Optional<User> user = getUserById(1);
user.ifPresent(u -> System.out.println("用户姓名: " + u.getName()));
}
}
```
#### 5.1.4 Stream API的介绍和使用
**练习任务**:
1. **Stream API练习**:
- 创建一个方法`findMaxValue`，该方法接收一个`List<Integer>`参数，并返回列表中的最大值。
- 使用Stream API来实现这个功能。
- 示例代码:
```java
import java.util.Arrays;
import java.util.List;
public class MaxFinder {
public static int findMaxValue(List<Integer> numbers) {
return numbers.stream().max(Integer::compare).orElse(0);
}
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
int maxValue = findMaxValue(numbers);
System.out.println("最大值: " + maxValue);
}
}
```
#### 5.1.5 泛型
**练习任务**:
1. **泛型练习**:
- 创建一个泛型类`Pair<T, U>`，用于存储两个不同类型的数据。
- 在主程序中创建一个`Pair<String, Integer>`对象，并设置和获取其中的值。
- 示例代码:
```java
public class Pair<T, U> {
private T first;
private U second;
public Pair(T first, U second) {
this.first = first;
this.second = second;
}
public T getFirst() {
return first;
}
public U getSecond() {
return second;
}
public void setFirst(T first) {
this.first = first;
}
public void setSecond(U second) {
this.second = second;
}
}
public class Main {
public static void main(String[] args) {
Pair<String, Integer> pair = new Pair<>("Hello", 42);
System.out.println("First: " + pair.getFirst() + ", Second: " + pair.getSecond());
}
}
```
### 5.2 Spring框架简介
#### 5.2.2 Spring框架的核心特性
**练习任务**:
1. **Spring框架特性练习**:
- 使用Spring框架创建一个简单的Web应用，该应用包含一个控制器，该控制器提供一个静态的欢迎页面。
- 示例代码:
```java
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
@Controller
public class WelcomeController {
@GetMapping("/")
public String welcome() {
return "welcome";
}
}
```
### 5.3 Spring IoC
#### 5.3.1 Spring Bean的定义和生命周期
**练习任务**:
1. **Bean生命周期练习**:
- 创建一个带有初始化和销毁方法的Spring Bean。
- 使用`@PostConstruct`和`@PreDestroy`注解来标记初始化和销毁方法。
- 示例代码:
```java
import org.springframework.stereotype.Component;
@Component
public class LifeCycleBean {
public LifeCycleBean() {
System.out.println("LifeCycleBean created.");
}
@PostConstruct
public void init() {
System.out.println("LifeCycleBean initialized.");
}
@PreDestroy
public void destroy() {
System.out.println("LifeCycleBean destroyed.");
}
}
```
#### 5.3.2 XML和注解方式的Bean配置
**练习任务**:
1. **XML和注解配置练习**:
- 使用XML和注解两种方式配置一个简单的Spring Bean。
- 在主程序中获取并使用该Bean。
- 示例代码 (XML配置):
```xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="myBean" class="com.example.MyBean">
<property name="name" value="John Doe"/>
</bean>
</beans>
```
- 示例代码 (注解配置):
```java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class AppConfig {
@Bean
public MyBean myBean() {
return new MyBean("Jane Doe");
}
}
public class MyBean {
private String name;
public MyBean(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
```
### 5.4 Spring MVC
#### 5.4.2 使用@Controller定义控制器
**练习任务**:
1. **控制器练习**:
- 创建一个简单的控制器，该控制器接收一个GET请求并返回一个简单的HTML页面。
- 示例代码:
```java
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
@Controller
public class SimpleController {
@GetMapping("/simple")
public String simplePage() {
return "simple";
}
}
```

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## 6. 数据库访问
### 6.1 JDBC
#### 6.1.3 实现第一个JDBC程序
**练习任务**:
1. **创建数据库表**:
- 根据PetClinic中的`Owner`实体模型创建一个表，包含`id`（整数，主键，自增）、`firstName`（字符串，长度255，不可为空）、`lastName`（字符串，长度255，不可为空）、`address`（字符串，长度255）、`city`（字符串，长度255）、`telephone`（字符串，长度255）字段。
- 示例代码:
```java
private static void createOwnerTable(Connection conn) throws SQLException {
String sql = "CREATE TABLE IF NOT EXISTS owners (" +
"id INT AUTO_INCREMENT PRIMARY KEY," +
"firstName VARCHAR(255) NOT NULL," +
"lastName VARCHAR(255) NOT NULL," +
"address VARCHAR(255)," +
"city VARCHAR(255)," +
"telephone VARCHAR(255))";
try (PreparedStatement stmt = conn.prepareStatement(sql)) {
stmt.executeUpdate();
}
}
```
2. **插入业主记录**:
- 向`owners`表中插入两条记录。
- 示例代码:
```java
private static void insertOwners(Connection conn) throws SQLException {
String sql = "INSERT INTO owners (firstName, lastName, address, city, telephone) VALUES (?, ?, ?, ?, ?)";
try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
pstmt.setString(1, "Alice");
pstmt.setString(2, "Johnson");
pstmt.setString(3, "123 Main St");
pstmt.setString(4, "Springfield");
pstmt.setString(5, "555-1234");
pstmt.executeUpdate();
pstmt.setString(1, "Bob");
pstmt.setString(2, "Smith");
pstmt.setString(3, "456 Elm St");
pstmt.setString(4, "Springfield");
pstmt.setString(5, "555-5678");
pstmt.executeUpdate();
}
}
```
3. **查询业主记录**:
- 查询`owners`表中的所有记录，并打印出每条记录的信息。
- 示例代码:
```java
private static void queryOwners(Connection conn) throws SQLException {
String sql = "SELECT * FROM owners";
try (PreparedStatement pstmt = conn.prepareStatement(sql);
ResultSet rs = pstmt.executeQuery()) {
while (rs.next()) {
int id = rs.getInt("id");
String firstName = rs.getString("firstName");
String lastName = rs.getString("lastName");
String address = rs.getString("address");
String city = rs.getString("city");
String telephone = rs.getString("telephone");
System.out.println("ID: " + id + ", First Name: " + firstName + ", Last Name: " + lastName + ", Address: " + address + ", City: " + city + ", Telephone: " + telephone);
}
}
}
```
4. **更新业主记录**:
- 更新`owners`表中名字为"Alice Johnson"的业主的电话号码为"555-1111"。
- 示例代码:
```java
private static void updateOwner(Connection conn) throws SQLException {
String sql = "UPDATE owners SET telephone = ? WHERE firstName = ? AND lastName = ?";
try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
pstmt.setString(1, "555-1111");
pstmt.setString(2, "Alice");
pstmt.setString(3, "Johnson");
int rowsUpdated = pstmt.executeUpdate();
System.out.println(rowsUpdated + " row(s) updated.");
}
}
```
5. **删除业主记录**:
- 删除`owners`表中名字为"Bob Smith"的业主记录。
- 示例代码:
```java
private static void deleteOwner(Connection conn) throws SQLException {
String sql = "DELETE FROM owners WHERE firstName = ? AND lastName = ?";
try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
pstmt.setString(1, "Bob");
pstmt.setString(2, "Smith");
int rowsDeleted = pstmt.executeUpdate();
System.out.println(rowsDeleted + " row(s) deleted.");
}
}
```
6. **完整程序**:
- 将以上步骤整合到一个完整的程序中，确保正确加载MySQL驱动、建立数据库连接，并处理异常。
- 示例代码:
```java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class JdbcCrudExample {
private static final String DB_URL = "jdbc:mysql://localhost:3306/petclinic";
private static final String USER = "root";
private static final String PASS = "password";
public static void main(String[] args) {
Connection conn = null;
try {
// 加载MySQL驱动
Class.forName("com.mysql.cj.jdbc.Driver");
// 获取数据库连接
conn = DriverManager.getConnection(DB_URL, USER, PASS);
// 创建表
createOwnerTable(conn);
// 插入记录
insertOwners(conn);
// 查询记录
queryOwners(conn);
// 更新记录
updateOwner(conn);
// 删除记录
deleteOwner(conn);
// 再次查询记录
queryOwners(conn);
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
// 其他方法...
}
```
### 6.3 SQL注入的预防措施
**练习任务**:
1. **使用PreparedStatement防止SQL注入**:
- 修改上述的`queryOwners`方法，使用`PreparedStatement`来执行查询。
- 示例代码:
```java
private static void queryOwners(Connection conn) throws SQLException {
String sql = "SELECT * FROM owners WHERE firstName = ? AND lastName = ?";
try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
pstmt.setString(1, "Alice");
pstmt.setString(2, "Johnson");
ResultSet rs = pstmt.executeQuery();
while (rs.next()) {
int id = rs.getInt("id");
String firstName = rs.getString("firstName");
String lastName = rs.getString("lastName");
String address = rs.getString("address");
String city = rs.getString("city");
String telephone = rs.getString("telephone");
System.out.println("ID: " + id + ", First Name: " + firstName + ", Last Name: " + lastName + ", Address: " + address + ", City: " + city + ", Telephone: " + telephone);
}
}
}
```
### 6.2 数据库连接池
#### 6.2.4 使用HikariCP实现数据库连接池
**练习任务**:
1. **配置HikariCP连接池**:
- 使用HikariCP配置一个连接池，并使用它来获取数据库连接。
- 示例代码:
```java
import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import java.sql.Connection;
import java.sql.SQLException;
public class HikariCpExample {
public static void main(String[] args) {
HikariConfig config = new HikariConfig();
config.setJdbcUrl("jdbc:mysql://localhost:3306/petclinic");
config.setUsername("root");
config.setPassword("password");
config.setMaximumPoolSize(10);
config.setConnectionTimeout(30000);
HikariDataSource ds = new HikariDataSource(config);
try (Connection conn = ds.getConnection()) {
// 使用连接执行数据库操作
System.out.println("Database connection established.");
} catch (SQLException e) {
e.printStackTrace();
}
}
}
```

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mvc开源项目参考 https://gitee.com/YHC/book-JavaEE-SSM
spring petclinic https://gitee.com/phxism/spring-framework-petclinic
https://gitee.com/univerciti/java-ee-spring-pet-clinic
https://github.com/FlaviodosSantos/TutorialSpringMVC
**https://github.com/spring-petclinic/spring-framework-petclinic**