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使用apache tomcat jdbc的jdbc池的singleton数据库类

java-8 jdbc tomcat oracle java

M.E. · 技术社区 · 6 年前

我正在尝试配置一个singleton数据库类,以允许使用JDK8和Tomcat7针对OracleXE18C数据库进行连接池。

由于以下错误,无法编译源:

未报告的异常sqlException;必须捕获或声明为投掷

类源代码:

package com.example.webapp.db;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import org.apache.tomcat.jdbc.pool.DataSource;
import org.apache.tomcat.jdbc.pool.PoolProperties;
public class DatabaseManager {

    private static final DatabaseManager SINGLE_INSTANCE = new DatabaseManager();

    private DatabaseManager() throws SQLException {
        PoolProperties p = new PoolProperties();
        p.setUrl("jdbc:oracle:thin:@localhost:1521:xe");
        p.setDriverClassName("oracle.jdbc.driver.OracleDriver");
        p.setUsername("scott");
        p.setPassword("tiger");
        p.setJmxEnabled(true);
        p.setTestWhileIdle(false);
        p.setTestOnBorrow(true);
        p.setValidationQuery("SELECT 1");
        p.setTestOnReturn(false);
        p.setValidationInterval(30000);
        p.setTimeBetweenEvictionRunsMillis(30000);
        p.setMaxActive(100);
        p.setInitialSize(10);
        p.setMaxWait(10000);
        p.setRemoveAbandonedTimeout(60);
        p.setMinEvictableIdleTimeMillis(30000);
        p.setMinIdle(10);
        p.setLogAbandoned(true);
        p.setRemoveAbandoned(true);
        p.setJdbcInterceptors("org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;"+
          "org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer");
        DataSource datasource = new DataSource();
        datasource.setPoolProperties(p); 

        Connection con = null;
        try {
          con = datasource.getConnection();
          Statement st = con.createStatement();
          ResultSet rs = st.executeQuery("select * from user");
          int cnt = 1;
          while (rs.next()) {
              System.out.println((cnt++)+". Host:" +rs.getString("Host")+
                " User:"+rs.getString("User")+" Password:"+rs.getString("Password"));
          }
          rs.close();
          st.close();
        } finally {
          if (con!=null) try {con.close();}catch (Exception ignore) {}
        }
    }

    public static DatabaseManager getInstance() {
        return SINGLE_INSTANCE;
    }
}

2 回复 | 直到 6 年前

deHaar 6 年前

我认为你应该扔或处理 SQLException 在 getInstance() 并使用 尝试使用资源 (自动关闭资源)而不是 finally 块。你应该不制作你的 instance 使用构造函数的常量,该构造函数将 Exception 用于初始化。

package com.example.webapp.db;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import org.apache.tomcat.jdbc.pool.DataSource;
import org.apache.tomcat.jdbc.pool.PoolProperties;

public class DatabaseManager {

    // not final anymore and null as default
    private static DatabaseManager instance = null;

    private DatabaseManager() {
        PoolProperties p = new PoolProperties();
        p.setUrl("jdbc:oracle:thin:@localhost:1521:xe");
        p.setDriverClassName("oracle.jdbc.driver.OracleDriver");
        p.setUsername("scott");
        p.setPassword("tiger");
        p.setJmxEnabled(true);
        p.setTestWhileIdle(false);
        p.setTestOnBorrow(true);
        p.setValidationQuery("SELECT 1");
        p.setTestOnReturn(false);
        p.setValidationInterval(30000);
        p.setTimeBetweenEvictionRunsMillis(30000);
        p.setMaxActive(100);
        p.setInitialSize(10);
        p.setMaxWait(10000);
        p.setRemoveAbandonedTimeout(60);
        p.setMinEvictableIdleTimeMillis(30000);
        p.setMinIdle(10);
        p.setLogAbandoned(true);
        p.setRemoveAbandoned(true);
        p.setJdbcInterceptors("org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;"
                + "org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer");
        javax.sql.DataSource datasource = new DataSource();
        datasource.setPoolProperties(p);

        // use a try-with resource to get rid of the finally block...
        try (Connection con = datasource.getConnection()) {
            Statement st = con.createStatement();
            ResultSet rs = st.executeQuery("select * from user");
            int cnt = 1;

            while (rs.next()) {
                System.out.println((cnt++) + ". Host:" + rs.getString("Host")
                        + " User:" + rs.getString("User")
                        + " Password:" + rs.getString("Password"));
            }

            rs.close();
            st.close();
        // ... and handle the exception
        } catch (SQLException e) {
            System.err.println("SQLException while constructing the instance of DatabaseManager");
            e.printStackTrace();
        }
    }

    public static DatabaseManager getInstance() {
        // check for null here:
        if (instance == null) {
            instance = new DatabaseManager();
        }
        return instance;
    }
}

也许,为数据库连接创建初始化方法比初始化构造函数中的所有内容更好,但这是基于观点的。

Ramesh Subramanian 6 年前

如下图所示更改代码,您必须捕获异常。

private static  DatabaseManager SINGLE_INSTANCE = null;
static {
    try {
        SINGLE_INSTANCE = new DatabaseManager();
    }
    catch(Exception e) {
        e.printStackTrace();
    }
}