以数据库连接为例，展示如何进行属性配置。
直接使用
JDBCUtil对数据库进行操作:
public class JDBCUtil {
public static final String URL = "jdbc:mysql://localhost:3306/jdbctest";
public static final String USER = "root";
public static final String PASSWORD = "password";
public static final String DRIVER = "com.mysql.cj.jdbc.Driver";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
// 1.加载驱动程序
Class.forName(DRIVER);
//2.获得数据库连接
conn = DriverManager.getConnection(URL, USER, PASSWORD);
//3.操作数据库
stmt = conn.createStatement();
//4.实现增删改查
rs = stmt.executeQuery("SELECT * FROM user;");
//如果有数据,rs.next()返回true
while (rs.next()) {
System.out.println("username= " + rs.getString("username") + ", password= "
+ rs.getString("password") + ", name= " + rs.getString("name"));
}
stmt.close();
conn.close();
} catch (ClassNotFoundException ex1) {
ex1.printStackTrace();
} catch (SQLException ex2) {
ex2.printStackTrace();
} finally {
if (rs != null) {
try {
rs.close();
} catch (SQLException sqlEx) {
//
}
rs = null;
if (stmt != null) {
try {
stmt.close();
} catch (SQLException sqlEx) {
//
}
conn = null;
if (conn != null) {
try {
conn.close();
} catch (SQLException sqlEx) {
//
}
conn = null; //垃圾回收机制会更早地垃圾释放
}
}
}
}
}其中，url、username、password、driverClassName等数据库连接所需的参数属性直接在代码中写死，后续如果有变化，需要更改所有使用的地方。所以，现在需要把这些属性从代码中单独抽取到配置文件中。
属性读取
将属性抽取到datasource.properties文件中:
# 驱动的Java类名
mydatasource.driverClassName=com.mysql.cj.jdbc.Driver
#传递给JDBC驱动的用于建立连接的URL
mydatasource.url=jdbc:mysql://localhost:3306/jdbctest?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
#用户名和密码
mydatasource.username=root
mydatasource.password=1234代码中使用DataSource对象：
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class DataSource {
private String driverClassName;
private String url;
private String username;
private String password;
}配置文件到对象的映射如下：
public class DataSourceFactory {
public static DataSource getDataSource() throws IOException {
InputStream inputStream = DataSourceFactory.class.getResourceAsStream("/datasource.properties");
Properties properties = new Properties();
properties.load(inputStream);
DataSource dataSource = DataSource.builder()
.driverClassName(properties.getProperty("mydatasource.driverClassName"))
.url(properties.getProperty("mydatasource.url"))
.username(properties.getProperty("mydatasource.username"))
.password(properties.getProperty("mydatasource.password"))
.build();
return dataSource;
}
}然后我们的数据库操作代码就变成了：
public class JDBCUtil {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
DataSource dataSource = DataSourceFactory.getDataSource();
// 1.加载驱动程序
Class.forName(dataSource.getUrl());
//2.获得数据库连接
conn = DriverManager.getConnection(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());
//3.操作数据库
stmt = conn.createStatement();
//4.实现增删改查
rs = stmt.executeQuery("SELECT * FROM user;");
//如果有数据,rs.next()返回true
while (rs.next()) {
System.out.println("username= " + rs.getString("username") + ", password= "
+ rs.getString("password") + ", name= " + rs.getString("name"));
}
stmt.close();
conn.close();
} catch (ClassNotFoundException ex1) {
ex1.printStackTrace();
} catch (Exception ex2) {
ex2.printStackTrace();
} finally {
if (rs != null) {
try {
rs.close();
} catch (SQLException sqlEx) {
//
}
rs = null;
if (stmt != null) {
try {
stmt.close();
} catch (SQLException sqlEx) {
//
}
conn = null;
if (conn != null) {
try {
conn.close();
} catch (SQLException sqlEx) {
//
}
conn = null; //垃圾回收机制会更早地垃圾释放
}
}
}
}
}
}PropertySource
在Spring项目中可以使用PropertySource配置文件到对象的映射:
# 驱动的Java类名
mydatasource.driverClassName=com.mysql.cj.jdbc.Driver
#传递给JDBC驱动的用于建立连接的URL
mydatasource.url=jdbc:mysql://localhost:3306/jdbctest?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
#用户名和密码
mydatasource.username=root
mydatasource.password=1234@Data
@Component
@PropertySource("datasource.properties")
public class DataSource {
@Value("${mydatasource.driverClassName}")
private String driverClassName;
@Value("${mydatasource.url}")
private String url;
@Value("${mydatasource.username}")
private String username;
@Value("${mydatasource.password}")
private String password;
}DataSource能够直接当作bean使用
ConfigurationProperties
在SpringBoot项目中可以使用ConfigurationProperties实现配置文件(application.yml或者application.properties) 到对象的映射:
# 驱动的Java类名
mydatasource.driverClassName=com.mysql.cj.jdbc.Driver
#传递给JDBC驱动的用于建立连接的URL
mydatasource.url=jdbc:mysql://localhost:3306/jdbctest?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
#用户名和密码
mydatasource.username=root
mydatasource.password=1234@Configuration
@ConfigurationProperties(prefix = "mydatasource")
@Data
public class DataSource {
private String driverClassName;
private String url;
private String username;
private String password;
}配置中心
如nacos：https://nacos.io/zh-cn/docs/quick-start-spring-boot.html
如nacos，见官方文档: https://nacos.io/zh-cn/docs/quick-start-spring-boot.html
- 添加依赖。
<dependency>
<groupId>com.alibaba.boot</groupId>
<artifactId>nacos-config-spring-boot-starter</artifactId>
<version>${latest.version}</version>
</dependency>- 在 application.properties 中配置 Nacos server 的地址：
nacos.config.server-addr=127.0.0.1:8848- 使用 @NacosPropertySource 加载 dataId 为 example 的配置源，并开启自动更新：
@SpringBootApplication
@NacosPropertySource(dataId = "example", autoRefreshed = true)
public class NacosConfigApplication {
public static void main(String[] args) {
SpringApplication.run(NacosConfigApplication.class, args);
}
}- 通过 Nacos 的 @NacosValue 注解设置属性值。
@Controller
@RequestMapping("config")
public class ConfigController {
@NacosValue(value = "${useLocalCache:false}", autoRefreshed = true)
private boolean useLocalCache;
@RequestMapping(value = "/get", method = GET)
@ResponseBody
public boolean get() {
return useLocalCache;
}
}