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项目规范：JSF 2.1 H2 Database Embedded Jetty Web Server Embedded

问题：我有一个支持 bean “AverageBPSCalc”，它有一个托管 bean “Frames”列表。frame 的 getter 方法检索数据库值并返回使用 dataTable 标记访问的 Frames 对象列表。框架的 getter 方法被调用三次，这不必要地浪费了连接池中的数据库连接。

代码：

支持豆

package com.tutorial;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import javax.faces.bean.ManagedProperty;

public class AverageBPSCalc
{
    private Date fromDt;
    private Date toDt;
    @ManagedProperty("#{dbConnector}")
    private DbConnector dbConnector;
    private List<Frames> frames;

    public Date getFromDt()
    {
        return fromDt;
    }

    public void setFromDt(Date fromDt)
    {
        this.fromDt = fromDt;
    }

    public Date getToDt()
    {
        return toDt;
    }

    public void setToDt(Date toDt)
    {
        this.toDt = toDt;
    }

    public List<Frames> getFrames()
    {
        System.out.println("In GET avg bps method");
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        DateFormat dateMod = new SimpleDateFormat("M/d/yyyy");
        DateFormat timeMod = new SimpleDateFormat("HH:mm:ss,SSS");
        try
        {
            List<Frames> frames = new ArrayList<Frames>();
            String avgBPSquery = "select CLKRX_DATE,CLKRX_TIME,bps_avg from frames where clkrx_date between '" + dateMod.format(fromDt) + "' and '" + dateMod.format(toDt)
                    + "' and CLKRX_TIME between '" + timeMod.format(fromDt) + "' and '" + timeMod.format(toDt) + "'";
            con = dbConnector.getCon();
            System.out.println("Active Connection :::: "+con);
            st = con.createStatement();
            rs = st.executeQuery(avgBPSquery);
            System.out.println("Query executing : "+avgBPSquery);
            while (rs.next())
            {
                Frames frame = new Frames();
                frame.setRecDate(rs.getString(1));
                frame.setRectime(rs.getString(2));
                frame.setBpsAvg(rs.getDouble(3));
                frames.add(frame);
            }
            this.frames = frames;
            rs.close();
            st.close();
            con.close();
        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }
        return frames;
    }

    public void setFrames(List<Frames> frames)
    {
        System.out.println("In SET avg bps method");
        this.frames = frames;
    }

    public DbConnector getDbConnector()
    {
        return dbConnector;
    }

    public void setDbConnector(DbConnector dbConnector)
    {
        this.dbConnector = dbConnector;
    }
}

结果视图 

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core">

<ui:composition template="/WEB-INF/templates/basetemplate.xhtml">
    <ui:define name="content">
        <h:head>
            <script type="text/javascript" src="raphael-min.js"></script>
            <script src="g.raphael.js" type="text/javascript"></script>
            <script type="text/javascript" src="g.line.js"></script>
            <script type="text/javascript" charset="utf-8">
                /* Graph Logic goes here. */
                window.onload = function() {
                    var r = Raphael("holder"), txtattr = {
                        font : "12px 'Fontin Sans', Fontin-Sans, sans-serif"
                    };
                    r.text(160, 100, "Average BPS").attr(txtattr);
                    var x = new Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
                    var y = new Array(10, 20, 30, 40, 50, 60, 70, 80, 90, 100);
                    /* r.linechart(160,130,100,100,x,y,{smooth: true, colors: ['#F00'], symbol: 'circle'}); */
                    r.linechart(160, 130, 200, 200, [ 1, 2, 3, 4, 5 ], [
                            [ 1, 2, 3, 4, 5 ], [ 1, 3, 9, 16, 25 ],
                            [ 100, 50, 25, 12, 6 ] ], {
                        smooth : true,
                        colors : [ '#F00', '#0F0', '#FF0' ],
                        symbol : 'circle',
                        axis : "0 0 1 1",
                        axisxstep : "10",
                        axisystep : "10"
                    });
                };
            </script>
            <h:outputStylesheet library="css" name="css/table-style.css" />
        </h:head>
        <h:body>
            <h:outputLabel value="Selected From Date: #{avgBn.fromDt}"></h:outputLabel>
            <br></br>
            <h:outputLabel value="Selected To Date: #{avgBn.toDt}"></h:outputLabel>
            <br></br>
            <h:dataTable value="#{avgBn.frames}" var="fm">
                <h:column>
                    <f:facet name="header">Recorded Date</f:facet>
                #{fm.recDate}</h:column>
                <h:column>
                    <f:facet name="header">Recorded Time</f:facet>
                #{fm.rectime}</h:column>
                <h:column>
                    <f:facet name="header">Average BPS</f:facet>
                #{fm.bpsAvg}</h:column>
            </h:dataTable>
            <h:panelGroup id="holder" layout="block">
            </h:panelGroup>
        </h:body>
    </ui:define>

</ui:composition>
</html>

Frames Managed Bean： 包com.tutorial；

public class Frames
{
    private String recDate;
    private String rectime;
    private Double bpsAvg;

    public String getRecDate()
    {
        return recDate;
    }

    public void setRecDate(String recDate)
    {
        this.recDate = recDate;
    }

    public String getRectime()
    {
        return rectime;
    }

    public void setRectime(String rectime)
    {
        this.rectime = rectime;
    }

    public Double getBpsAvg()
    {
        return bpsAvg;
    }

    public void setBpsAvg(Double bpsAvg)
    {
        this.bpsAvg = bpsAvg;
    }
}
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