springboot進階功能（七）在資料庫中擷取application配置

1.代碼

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Map;
 
import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.boot.origin.OriginTrackedValue;
import org.springframework.context.ApplicationListener;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
 
 
public class ConfigureListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent> {
 
    @Override
    public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        // 擷取spring Environment
        MutablePropertySources propertySources = event.getEnvironment().getPropertySources();
        // 配置放在了application-pro或者是application-dev 中 指派複制需要在其中指派
        for (PropertySource<?> propertySource : propertySources) {
            boolean applicationConfig = propertySource.getName().contains("application-");
            if (!applicationConfig) {
                continue;
            }
            // 擷取上文的application集合中擷取資料庫連接配接
            Map<String, OriginTrackedValue> dataBaseSource =
                (Map<String, OriginTrackedValue>)propertySource.getSource();
            String driverClass = String.valueOf(dataBaseSource.get("spring.datasource.driver-class-name").getValue());
            String url = String.valueOf(dataBaseSource.get("spring.datasource.url").getValue());
            String user = String.valueOf(dataBaseSource.get("spring.datasource.username").getValue());
            String password = String.valueOf(dataBaseSource.get("spring.datasource.password").getValue());
            // 因為在spring初始化之前 所有不能使用注解 是以需要jdbc直接連接配接資料庫 首先建立驅動
            try {
                Class.forName("oracle.jdbc.driver.OracleDriver");
                conn = DriverManager.getConnection(url, user, password);
                // 1、擷取連接配接對象
                // 2、建立statement類對象，用來執行SQL語句！！
                st = conn.createStatement();
                // 3、建立sql查詢語句
                String sql = "select * from SYS_CONFIGURE";
                // 4、執行sql語句并且換回一個查詢的結果集
                rs = st.executeQuery(sql);
                while (rs.next()) {
                    // 擷取資料庫中的資料
                    String item = rs.getString("ITEM");
                    String itemValue = rs.getString("ITEM_VALUE");
                    // 通過資料庫中的配置 修改application集合中資料
                    Map<String, OriginTrackedValue> source =
                        (Map<String, OriginTrackedValue>)propertySource.getSource();
                    OriginTrackedValue originTrackedValue = source.get(item);
                    OriginTrackedValue newOriginTrackedValue =
                        OriginTrackedValue.of(itemValue, originTrackedValue.getOrigin());
                    source.put(item, newOriginTrackedValue);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}      

@SpringBootApplication
public class TestApplication {
 
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(TestApplication.class);
        app.addListeners(new ConfigureListener());
        app.run(args);
    }
}      

2.簡介

在spring boot初始化時 會讀取application 放在MutablePropertySources 中 我們會讀取配置MutablePropertySources 然後查詢資料庫 根據key查詢之後 重新覆寫（因為以上操作時 bean factory還沒有初始化 是以用jdbc） 

而以上攔截器會在讀取application後立刻執行 不會馬後炮（當spring boot初始化之後在更改MutablePropertySources ）

擷取MutablePropertySources 
MutablePropertySources propertySources = event.getEnvironment().getPropertySources();