【DataBase】H2 DateBase与项目集成

　　本例介绍H2与web项目的集成

项目启动H2数据库

　　1、新建Maven Web项目，参考：【Maven】Eclipse 使用Maven创建Java Web项目

　　2、引入h2的jar包依赖

 <dependency>
     <groupId>com.h2database</groupId>
     <artifactId>h2</artifactId>
     <version>1.4.199</version>
 </dependency>

　　3、编辑web.xml文件，注册h2内置的监听器，监听ServletContext 对象启动，而启动H2数据库

 <!-- 监听启动H2 DB -->
 <listener>
     <listener-class>org.h2.server.web.DbStarter</listener-class>
 </listener>

 <!-- H2 DB 参数 -->
 <context-param>
     <param-name>db.url</param-name>
     <param-value>jdbc:h2:/D:/data/sample</param-value>
 </context-param>
 <context-param>
     <param-name>db.user</param-name>
     <param-value>sa</param-value>
 </context-param>
 <context-param>
     <param-name>db.password</param-name>
     <param-value></param-value>
 </context-param>
 <!-- 运行其他服务器访问 -->
 <context-param>
     <param-name>db.tcpServer</param-name>
     <param-value>-tcpAllowOthers</param-value>
 </context-param>

　　　　org.h2.server.web.DbStarter监听器代码如下，可以看到监听器创建的H2数据库，并且将一个数据库连接放入ServletContext 对象中。

 /*
  * Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
  * and the EPL 1.0 (http://h2database.com/html/license.html).
  * Initial Developer: H2 Group
  */
 package org.h2.server.web;

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.Statement;

 import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletContextListener;

 import org.h2.tools.Server;
 import org.h2.util.StringUtils;

 /**
  * This class can be used to start the H2 TCP server (or other H2 servers, for
  * example the PG server) inside a web application container such as Tomcat or
  * Jetty. It can also open a database connection.
  */
 public class DbStarter implements ServletContextListener {

     private Connection conn;
     private Server server;

     @Override
     public void contextInitialized(ServletContextEvent servletContextEvent) {
         try {
             org.h2.Driver.load();

             // This will get the setting from a context-param in web.xml if
             // defined:
             ServletContext servletContext = servletContextEvent.getServletContext();
             String url = getParameter(servletContext, "db.url", "jdbc:h2:~/test");
             String user = getParameter(servletContext, "db.user", "sa");
             String password = getParameter(servletContext, "db.password", "sa");

             // Start the server if configured to do so
             String serverParams = getParameter(servletContext, "db.tcpServer", null);
             if (serverParams != null) {
                 String[] params = StringUtils.arraySplit(serverParams, ' ', true);
                 server = Server.createTcpServer(params);
                 server.start();
             }

             // To access the database in server mode, use the database URL:
             // jdbc:h2:tcp://localhost/~/test
             conn = DriverManager.getConnection(url, user, password);
             servletContext.setAttribute("connection", conn);
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

     private static String getParameter(ServletContext servletContext,
             String key, String defaultValue) {
         String value = servletContext.getInitParameter(key);
         return value == null ? defaultValue : value;
     }

     /**
      * Get the connection.
      *
      * @return the connection
      */
     public Connection getConnection() {
         return conn;
     }

     @Override
     public void contextDestroyed(ServletContextEvent servletContextEvent) {
         try {
             Statement stat = conn.createStatement();
             stat.execute("SHUTDOWN");
             stat.close();
         } catch (Exception e) {
             e.printStackTrace();
         }
         try {
             conn.close();
         } catch (Exception e) {
             e.printStackTrace();
         }
         if (server != null) {
             server.stop();
             server = null;
         }
     }

 }

　　4、编辑测试Servlet，SampleServlet.java类

 package com.test.h2.servlet;

 import java.io.IOException;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.Statement;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 public class SampleServlet extends HttpServlet {

     /**
      *
      */
     private static final long serialVersionUID = 1L;

     @Override
     protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         // 从ServletContext获取 连接对象
         Connection con = (Connection) getServletContext().getAttribute("connection");

         try {
             // 新建数据表
             String ctreateTable = "DROP TABLE test IF EXISTS; create table test(id integer,name VARCHAR(22) )";
             Statement createStatement = con.createStatement();
             long f1 = createStatement.executeUpdate(ctreateTable);
             System.out.println("创建表：" + f1);

             // 插入数据
             String insertSql = "INSERT INTO test VALUES(1,'小明')";
             Statement insertStatement = con.createStatement();
             long f2 = insertStatement.executeUpdate(insertSql);
             System.out.println("插入数据：" + f2);

             // 查询数据
             String selectSql = "select id,name from test";
             PreparedStatement prepareStatement = con.prepareStatement(selectSql);
             // 发送SQL 返回一个ResultSet
             ResultSet rs = prepareStatement.executeQuery();

             // 编历结果集
             while (rs.next())// 从数据库的取一行数据，是否还有下一行
             {
                 int id = rs.getInt(1); // 从1开始
                 String name = rs.getString(2);
                 System.out.println("id:" + id + "\t名称:" + name);
             }
             resp.getWriter().print("SUCCESS");
         } catch (Exception e) {
             resp.getWriter().print("FAILE");
         }

     }

 }

　　5、在web.xml中，注册SampleServlet

 <servlet>
     <servlet-name>SampleServlet</servlet-name>
     <servlet-class>com.test.h2.servlet.SampleServlet</servlet-class>
 </servlet>
 <servlet-mapping>
     <servlet-name>SampleServlet</servlet-name>
     <url-pattern>/sample</url-pattern>
 </servlet-mapping>

　　6、将项目发布到tomcat中，并启动，在浏览器中输入地址：http://localhost:8080/test-h2/sample，进行访问

　　　　

使用H2控制台Servlet

　　7、在项目中集成H2控制台，在web.xml文件中注册h2 jar包中内置的Servlet

 <!-- 使用H2控制台Servlet -->
 <servlet>
     <servlet-name>H2Console</servlet-name>
     <servlet-class>org.h2.server.web.WebServlet</servlet-class>
     <!--
     <init-param>
         <param-name>webAllowOthers</param-name>
         <param-value></param-value>
     </init-param>
     <init-param>
         <param-name>trace</param-name>
         <param-value></param-value>
     </init-param>
     -->
     <load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
     <servlet-name>H2Console</servlet-name>
     <url-pattern>/console/*</url-pattern>
 </servlet-mapping>
 <!--
 <security-role>
     <role-name>admin</role-name>
 </security-role>
 <security-constraint>
     <web-resource-collection>
         <web-resource-name>H2 Console</web-resource-name>
         <url-pattern>/console/*</url-pattern>
     </web-resource-collection>
     <auth-constraint>
         <role-name>admin</role-name>
     </auth-constraint>
 </security-constraint>
 -->

　　8、重启服务，在浏览器中输入地址：http://localhost:8080/test-h2/console进行访问

　　　　

向H2数据库注册自定义的数据库函数

　　9、编辑自定义函数类H2DBFunctionExt.java

 package com.test.h2.function;

 import java.util.UUID;

 /**
  * 对H2数据库函数的扩展
  * @author hd
  * @date 2019-05-28 18:46:07
  *
  */
 public class H2DBFunctionExt {

     /**
      * 用法：SELECT myid();
      * @return
      */
     public static String myid(){
         return UUID.randomUUID().toString().replaceAll("-", "");
     }

 }

　　10、编辑数据库注册监听类RegisterH2ExtFuncListener.java

 package com.test.h2.listener;

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

 import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletContextListener;

 public class RegisterH2ExtFuncListener implements ServletContextListener {

     @Override
     public void contextInitialized(ServletContextEvent servletContextEvent) {

         ServletContext servletContext = servletContextEvent.getServletContext();

         // 1、注册myid函数的SQL语句，语句格式：CREATE ALIAS [IF NOT EXISTS] newFunctionAliasName [DETERMINISTIC] FOR classAndMethodName
         String sql = "CREATE ALIAS IF NOT EXISTS myid  FOR \"com.test.h2.function.H2DBFunctionExt.myid\"";

         // 2、从ServletContext获取 连接对象
         Connection con = (Connection) servletContext.getAttribute("connection");
         try {

             // 3、获取Statement对象
             Statement stmt = con.createStatement();

             // 4、执行sql
             stmt.execute(sql);

             System.out.println("H2数据库扩展函数注册成功！");

         } catch (SQLException e) {
             // TODO Auto-generated catch block
             System.out.println("H2数据库扩展函数注册失败！");
             e.printStackTrace();
         }
     }

     @Override
     public void contextDestroyed(ServletContextEvent servletContextEvent) {
         // TODO Auto-generated method stub
         ServletContextListener.super.contextDestroyed(servletContextEvent);
     }

 }

　　11、注册监听器，注意放在H2启动监听器之后

 <!-- 注册RegisterH2ExtFuncListener监听器 -->
 <listener>
     <listener-class>com.test.h2.listener.RegisterH2ExtFuncListener</listener-class>
 </listener>

　　12、重启项目，登录H2控制台，使用sql：SELECT myid(); 查询

　　　　

　　与Spring集成参考：【DataBase】Hsqldb与项目集成