Java Web数据源详解_java web为什么要使用数据源?怎样做才能使用-优快云博客

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Java Web数据源详解

Java Web连接数据库一般有直接JDBC和数据源两种方式，

1、JDBC：

在MySQL中创建数据库：

drop    database if exists login;
create database login;
use login;
create table user (
   username        varchar ( 50 )    not null ,
   password        varchar ( 50 ) ,
    primary key    (username)
);

insert into user (username,password) values ("CoderDream", " 12345678 ");

测试代码：

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

public class Test {
     public static void main(String[] args) {
         try {
             // A: 1、2 都可以
             // Class.forName("org.gjt.mm.mysql.Driver"); // 1
            Class.forName( " com.mysql.jdbc.Driver " ); // 2

             // B: 连接数据库，用户名为：root，密码为空
            Connection conn = DriverManager.getConnection(
                     " jdbc:mysql://localhost:3306/login " , " root " , "" );

             // C: 创建 Statement
            Statement stmt = conn.createStatement();

             // D: 查询数据库中用户 CoderDream 的密码字段
            String sql = " select password from user where username ='CoderDream' " ;

             // E: 得到结果集
            ResultSet rs = stmt.executeQuery(sql);

             // F: 处理结果集，简单的输出password
             while (rs.next()) {
                System.out.print(rs.getString( " password " )); // 输出结果为 12345678
            }

             // G: 关闭资源
            rs.close();
            stmt.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

在Struts中一般会写一个公用类，用于连接数据库：
A、创建数据库：ADDRESSBOOKSAMPLE.sql

DROP DATABASE IF EXISTS ADDRESSBOOKSAMPLE;
CREATE DATABASE ADDRESSBOOKSAMPLE;
USE ADDRESSBOOKSAMPLE;
CREATE TABLE ADDRESSBOOK_TABLE(ID INT ( 4 ) AUTO_INCREMENT NOT NULL PRIMARY KEY ,NAME VARCHAR ( 25 ), PHONE VARCHAR ( 10 ), ADDRESS VARCHAR ( 50 ));
INSERT INTO ADDRESSBOOK_TABLE VALUES ( 1 , ' Wang ' , ' 56671234 ' , ' Beijing,Haidian ' );
INSERT INTO ADDRESSBOOK_TABLE VALUES ( 2 , ' Zhang ' , ' 45664568 ' , ' Shanghai,Pudong ' );
INSERT INTO ADDRESSBOOK_TABLE VALUES ( 3 , ' Cheng ' , ' 56643456 ' , ' Tianjing ' );
INSERT INTO ADDRESSBOOK_TABLE VALUES ( 4 , ' Zhao ' , ' 56789988 ' , ' Hainan ' );
INSERT INTO ADDRESSBOOK_TABLE VALUES ( 5 , ' Cao ' , ' 56498543 ' , ' Heibei ' );

B、公用类：DbUtil.java

package addressbook.model;

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

/**
* <strong>DbUtil</strong> is a utility class to create a connection to our
* sample database.
*/
public class DbUtil {
     static String driverName = " com.mysql.jdbc.Driver " ;
     static String dbUrl = " jdbc:mysql:// " ;

     public DbUtil() {

    }

     public static Connection connectToDb(String hostName, String databaseName)
             throws Exception {
        Connection connection = null ;
        String connName = dbUrl + hostName + " :3306 " + " / " + databaseName;
        Class.forName(driverName).newInstance();
        connection = DriverManager.getConnection(connName, " root " , "" );
         return connection;
    }

     public static Connection connectToDb(String databaseName) throws Exception {
         return (connectToDb( " localhost " , databaseName));
    }

     public static Connection connectToDb() throws Exception {
         return (connectToDb( " localhost " , " addressbooksample " ));
    }
}

C、JavaBean中调用公用类：

     public void insert() throws Exception {
        Connection con = DbUtil.connectToDb();
        PreparedStatement pStmt = null ;
         try {
            pStmt = con.prepareStatement( " INSERT INTO " + Constants.TABLENAME
                     + " (name,phone,address) " + " values(?,?,?) " );
            con.setAutoCommit( false );

            pStmt.setString( 1 , name);
            pStmt.setString( 2 , phone);
            pStmt.setString( 3 , address);
            pStmt.executeUpdate();
            con.commit();
        } catch (Exception ex) {
             try {
                con.rollback();
            } catch (SQLException sqlex) {
                sqlex.printStackTrace(System.out);
            }
             throw ex;
        } finally {
             try {
                pStmt.close();
                con.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

     public static Vector search(String strSql) throws Exception {
        Vector addressbookBeans = new Vector();
        Connection con = DbUtil.connectToDb();
        PreparedStatement pStmt = null ;
        ResultSet rs = null ;
         try {
            pStmt = con.prepareStatement(strSql);
            rs = pStmt.executeQuery();
             while (rs.next()) {
                addressbookBeans.add( new AddressBookBean(rs.getString( " NAME " ),
                        rs.getString( " PHONE " ), rs.getString( " ADDRESS " )));
            }
             return addressbookBeans;
        } finally {
             try {
                rs.close();
                pStmt.close();
                con.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

2、一般数据源配置

在struts-config.xml的<data-sources>标签中加入：

< data-sources >
         < data-source type ="org.apache.commons.dbcp.BasicDataSource" >
             < set-property property ="autoCommit" value ="true" />
             < set-property property ="description"
                value ="MySQL Data Source" />
             <set-property property="driverClassName"
                value ="com.mysql.jdbc.Driver" />
             < set-property property ="maxCount" value ="10" />
             < set-property property ="minCount" value ="2" />
             < set-property property ="username" value ="root" />
             < set-property property ="password" value ="" />
             < set-property property ="url"
                value ="jdbc:mysql://localhost:3306/addressbooksample" />
         </ data-source >
     </ data-sources >

同时导入以下包：
mysql-connector-java-5.1.0-bin.jar
commons-dbcp-1.2.2.jar
commons-pool-1.3.jar

注意：这里有个一个属性“ property ="driverClassName"”千万要写成"driverClassName"，而不是“driverClass”，否则会找不到！
孙卫琴的《精通Struts》就是漏掉了Name，让我调试了一个下午。
org.apache.commons.dbcp.BasicDataSource

     protected synchronized DataSource createDataSource()
         throws SQLException {

         // Load the JDBC driver class
         if (driverClassName != null ) {
             try {
                Class.forName(driverClassName);
            } catch (Throwable t) {
                String message = " Cannot load JDBC driver class ' " +
                    driverClassName + " ' " ;
                logWriter.println(message);
                t.printStackTrace(logWriter);
                 throw new SQLNestedException(message, t);
            }
        }

         // Create a JDBC driver instance
        Driver driver = null ;
         try {
            driver = DriverManager.getDriver(url);
        } catch (Throwable t) {
            String message = " Cannot create JDBC driver of class ' " +
                (driverClassName != null ? driverClassName : "" ) +
                 " ' for connect URL ' " + url + " ' " ;
            logWriter.println(message);
            t.printStackTrace(logWriter);
             throw new SQLNestedException(message, t);
        }
}

从源代码我们可以看到，如果不是“driverClassName”，就会得不到相应的类名，后面的getDriver(url)就会抛出异常：

[ERROR] ActionServlet - Initializing application data source org.apache.struts.action.DATA_SOURCE < org.apache.commons.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL ' jdbc:mysql://localhost:3306/addressbooksample ' > org.apache.commons.dbcp.SQLNestedException: Cannot create JDBC driver of class ' ' for connect URL 'jdbc:mysql://localhost:3306/addressbooksample'
    at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java: 1150 )
    at org.apache.commons.dbcp.BasicDataSource.setLogWriter(BasicDataSource.java: 959 )
    at org.apache.struts.action.ActionServlet.initModuleDataSources(ActionServlet.java: 778 )
    at org.apache.struts.action.ActionServlet.init(ActionServlet.java: 331 )
    at javax.servlet.GenericServlet.init(GenericServlet.java: 212 )
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java: 1139 )
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java: 966 )
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java: 3956 )
    at org.apache.catalina.core.StandardContext.start(StandardContext.java: 4230 )
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java: 760 )
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java: 740 )
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java: 544 )
    at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java: 920 )
    at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java: 883 )
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java: 492 )
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java: 1138 )
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java: 311 )
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java: 120 )
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java: 1022 )
    at org.apache.catalina.core.StandardHost.start(StandardHost.java: 736 )
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java: 1014 )
    at org.apache.catalina.core.StandardEngine.start(StandardEngine.java: 443 )
    at org.apache.catalina.core.StandardService.start(StandardService.java: 448 )
    at org.apache.catalina.core.StandardServer.start(StandardServer.java: 700 )
    at org.apache.catalina.startup.Catalina.start(Catalina.java: 552 )
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java: 39 )
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java: 25 )
    at java.lang.reflect.Method.invoke(Method.java: 597 )
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java: 295 )
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java: 433 )
Caused by: java.sql.SQLException: No suitable driver
    at java.sql.DriverManager.getDriver(DriverManager.java: 264 )
    at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java: 1143 )

30 more

提示class ' '不能连接URL！

数据源配置好了以后，我们就可以在Action中得到DataSource。
在InsertAction的execute()方法中：

            DataSource ds = getDataSource(request);
            Connection con = ds.getConnection();

            bean.insert(con);

这样，改写Bean中的insert()方法和search()方法，传入参数增加一个“Connection con”：

     public void insert(Connection con) throws Exception {
        PreparedStatement pStmt = null ;
         try {
            pStmt = con.prepareStatement( " INSERT INTO " + Constants.TABLENAME
                     + " (name,phone,address) " + " values(?,?,?) " );
            con.setAutoCommit( false );

            pStmt.setString( 1 , name);
            pStmt.setString( 2 , phone);
            pStmt.setString( 3 , address);
            pStmt.executeUpdate();
            con.commit();
        } catch (Exception ex) {
             try {
                con.rollback();
            } catch (SQLException sqlex) {
                sqlex.printStackTrace(System.out);
            }
             throw ex;
        } finally {
             try {
                pStmt.close();
                con.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

     public static Vector search(Connection con, String strSql) throws Exception {
        Vector addressbookBeans = new Vector();
        PreparedStatement pStmt = null ;
        ResultSet rs = null ;
         try {
            pStmt = con.prepareStatement(strSql);
            rs = pStmt.executeQuery();
             while (rs.next()) {
                addressbookBeans.add( new AddressBookBean(rs.getString( " NAME " ),
                        rs.getString( " PHONE " ), rs.getString( " ADDRESS " )));
            }
             return addressbookBeans;
        } finally {
             try {
                rs.close();
                pStmt.close();
                con.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

这样就不需使用数据库工具类 DbUtil 了。

3、插件方式，任何地方都可以得到数据源。

以一般方式配置的数据源有一个局限性，就是只能在Action中得到，因为要用到HttpServletRequest作为参数来得到数据源。

解决的办法是写一个插件，这个插件实现了Struts的PlugIn接口。

通过这个插件，我们可以在任何类中（包括Action、JavaBean和其他类）直接得到数据源，并建立连接：

package addressbook.plug;

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

import javax.sql.DataSource;

import org.apache.struts.action.ActionServlet;
import org.apache.struts.action.PlugIn;
import org.apache.struts.config.ModuleConfig;

public class Conn implements PlugIn {

     private static DataSource dataSource = null ;
     private Connection conn = null ;
     private PreparedStatement preStmt = null ;
     private Statement stmt = null ;

     // 得到数据源
     public void init(ActionServlet servlet, ModuleConfig config) {
        dataSource = (DataSource) servlet.getServletContext().getAttribute(
                 " org.apache.struts.action.DATA_SOURCE " );
    }

     public Conn() throws SQLException {
         if (dataSource != null ) {
            conn = dataSource.getConnection();
        }
    }

     public ResultSet executeQuery(String sql) {
        ResultSet rs = null ;

         try {
             if (stmt == null ) {
                stmt = conn.createStatement();
            }

            rs = stmt.executeQuery(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }

         return rs;
    }

     public void executeUpdate(String sql) throws SQLException {
         if (stmt == null ) {
            stmt = conn.createStatement();
        }

        stmt.executeUpdate(sql);
    }

     public Connection getConn() {
         return conn;
    }

     public void prepareStatement(String sqlStr) throws SQLException {
        preStmt = conn.prepareStatement(sqlStr);
    }

     public void setString( int index, String value) throws SQLException {
        preStmt.setString(index, value);
    }

     public void setInt( int index, int value) throws SQLException {
        preStmt.setInt(index, value);
    }

     public void setBoolean( int index, boolean value) throws SQLException {
        preStmt.setBoolean(index, value);
    }

     public void setLong( int index, long value) throws SQLException {
        preStmt.setLong(index, value);
    }

     public void setFloat( int index, float value) throws SQLException {
        preStmt.setFloat(index, value);
    }

     public void setBytes( int index, byte [] value) throws SQLException {
        preStmt.setBytes(index, value);
    }

     public void clearPreStmt() throws SQLException {
        preStmt.clearParameters();
        preStmt = null ;
    }

     public ResultSet executeQuery() throws SQLException {
         if (preStmt != null ) {
             return preStmt.executeQuery();
        } else {
             return null ;
        }
    }

     public void executeUpdate() throws SQLException {
         if (preStmt != null ) {
            preStmt.executeUpdate();
        }
    }

     public void close() {
         try {
             if (stmt != null ) {
                stmt.close();
                stmt = null ;
            }

             if (preStmt != null ) {
                preStmt.close();
                preStmt = null ;
            }

             if (conn != null ) {
                conn.close();
                conn = null ;
                System.out.println( " **** a connection is closed **** " );
            }
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }
    }

     public void destroy() {
    }
}

在struts-config.xml中配置数据源：

< data-sources >
         < data-source key ="org.apache.struts.action.DATA_SOURCE"
            type ="org.apache.commons.dbcp.BasicDataSource" >
             < set-property property ="autoCommit" value ="true" />
             < set-property property ="description"
                value ="MySQL Data Source" />
             < set-property property ="driverClassName"
                value ="com.mysql.jdbc.Driver" />
             < set-property property ="maxCount" value ="10" />
             < set-property property ="minCount" value ="2" />
             < set-property property ="username" value ="root" />
             < set-property property ="password" value ="" />
             < set-property property ="url"
                value ="jdbc:mysql://localhost:3306/addressbooksample" />
         </ data-source >
     </ data-sources >

同时在struts-config.xml文件的最后配置PlugIn