二进制数据直接保存到文件和从文件中读出非常的简单。和普通的数据库操作差别不大。只是用到部分流操作。例如各种输入输出流操作。所以深刻理解流操是非常重要的。
在此我借助于一个JSP的简单实例进行讲解。此实例保存职员数据，其中职员数据包含一个图片列。此列保存每名员工的照片。在此将照片直接保存到数据库中。首先建立职员信息表EmployeeInfo，表列非常的简单
employeeId:职员编号（自动增长）；employeeName:职员姓名；age:职员年龄；pic:职员图片（image类型）
首先讲解信息的保存。先建立一个录入界面index.jsp，其中包含一个元素，用于让用户选择图片文件。
页面代码如下（不做过多讲解）：
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
页面请求addServlet，获取录入信息，并调用JavaBean实现数据保存。Servlet代码如下：
package com.frank.action;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.frank.rule.*;
public class AddServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public AddServlet() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String employeeName=request.getParameter("employeeName");
int age=Integer.parseInt(request.getParameter("age"));
String pic=request.getParameter("pic");
EmployeeDAO employeeDAO=new EmployeeDAO();
if(employeeDAO.employeeAdd(employeeName, age, pic))
response.sendRedirect("success.jsp");
else
response.sendRedirect("index.jsp");
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
此Servlet只是简单的获取页面输入的数据，其中获取的Pic为用户选择的图片路径。严格讲，获取文件需要经过验证，防止非法图片的选择，这个可以根据自己的需要改善。然后Servlet调用业务类，将获取的数据通过参数传入，进行数据的增加。其中employeeAdd方法实现数据的保存，代码如下：
public boolean employeeAdd(String employeeName,int age,String pic){
Connection conn=null;
PreparedStatement pstmt=null;
FileInputStream fis=null;
try{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
conn=DriverManager.getConnection("jdbc:jtds:sqlserver://localhost:1433/SampleDB","sa","");
fis=new FileInputStream(pic);
String strSQL="INSERT INTO employeeInfo VALUES(?,?,?)";
pstmt=conn.prepareStatement(strSQL);
pstmt.setString(1, employeeName);
pstmt.setInt(2, age);
pstmt.setBinaryStream(3, fis, fis.available());
if(pstmt.executeUpdate()>0)
return true;
else
return false;
}catch(ClassNotFoundException ex){
ex.printStackTrace();
return false;
}catch(SQLException ex){
ex.printStackTrace();
return false;
}catch(IOException ex){
ex.printStackTrace();
return false;
}finally{
try{
fis.close();
pstmt.close();
conn.close();
}catch(Exception ex){
}
}
}
注意粗体部分，用获取的pic信息（文件路径）创建文件输入流对象，增加pic字段的内容通过流对象增加。
pstmt.setBinaryStream(3, fis, fis.available());
三个参数分别为：参数索引，流对象，流对象大小
当增加成功时，重定向到success.jsp
运行结果如下：
增加后，显示如下代表成功：
那么如何验证图片数据是否保存到了数据库中呢？我们通过再次检索增加的数据，读出增加的图片数据并在页面中显示出来进行验证。
首先建立一个非常简单的页面search.jsp，此页面通过文本框使用户输入要检索的人员的姓名，检索人员的基本信息（不检索图片数据），将检索的人员数据形成JOPO对象，保存到session中，以便页面使用。
POJO类（EmployeeObj)
package com.frank.obj;
public class EmployeeObj {
private int employeeId;
private String employeeName;
private int age;
public int getEmployeeId() {
return employeeId;
}
public void setEmployeeId(int employeeId) {
this.employeeId = employeeId;
}
public String getEmployeeName() {
return employeeName;
}
public void setEmployeeName(String employeeName) {
this.employeeName = employeeName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
search.jsp页面代码如下：
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
通过searchServlet实现基本信息的检索
package com.frank.action;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.frank.obj.EmployeeObj;
import com.frank.rule.EmployeeDAO;
public class SearchServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public SearchServlet() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String employeeName=request.getParameter("employeeName");
EmployeeDAO employeeDAO=new EmployeeDAO();
EmployeeObj employeeObj=employeeDAO.getEmployeeByName(employeeName);
HttpSession session=request.getSession();
session.setAttribute("employee", employeeObj);
response.sendRedirect("display.jsp");
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
此Servlet调用业务类的getEmployeeByName方法检索人员基本信息，返回EmployeeObj对象，并放入session中，当然也可以放入request中，根据自己的需要改进。页面检索成功后重定向到display.jsp进行信息的显示（稍后讲解）
getEmployeeByName方法代码如下：
public EmployeeObj getEmployeeByName(String employeeName){
Connection conn=null;
PreparedStatement pstmt=null;
ResultSet rst=null;
EmployeeObj employeeObj=new EmployeeObj();
try{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
conn=DriverManager.getConnection("jdbc:jtds:sqlserver://localhost:1433/SampleDB","sa","");
String strSQL="SELECT employeeId,employeeName,age FROM EmployeeInfo WHERE employeeName=?";
pstmt=conn.prepareStatement(strSQL);
pstmt.setString(1, employeeName);
rst=pstmt.executeQuery();
if(rst.next()){
employeeObj.setEmployeeId(rst.getInt("employeeId"));
employeeObj.setEmployeeName(rst.getString("employeeName"));
employeeObj.setAge(rst.getInt("age"));
return employeeObj;
}
return null;
}catch(ClassNotFoundException ex){
ex.printStackTrace();
return null;
}catch(SQLException ex){
ex.printStackTrace();
return null;
}finally{
try{
pstmt.close();
conn.close();
}catch(Exception ex){
}
}
}
display.jsp负责显示查询出的结果信息，代码如下：
<%@ page language="java" import="java.util.*,com.frank.obj.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<%
EmployeeObj employeeObj=(EmployeeObj)session.getAttribute("employee");
%>
| EmployeeId | <%=employeeObj.getEmployeeId() %> |
| EmployeeName | <%=employeeObj.getEmployeeName() %> |
| Age | <%=employeeObj.getAge() %> |
| Pic |
代码非常的简单，只是简单的从session中获取保存的EmployeeObj对象，然后利用jsp表达式将数据成员信息显示到页面上。但是注意粗体部分，因为我们需要将保存的图片数据读出，然后显示成图片。所以在此我们利用Img元素显示图片，而Src利用displayServlet的运行结果输出到客户端，作为图片的显示源。displayServlet包含参数employeeId，用来决定具体显示哪一员工的图片。
displayServlet通过Servlet输出流，将读取的图片数据发送到客户端，代码如下：
package com.frank.action;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.frank.rule.EmployeeDAO;
public class DisplayServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public DisplayServlet() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("image/gif");
int employeeId=Integer.parseInt(request.getParameter("employeeId"));
EmployeeDAO employeeDAO=new EmployeeDAO();
InputStream is=employeeDAO.getPicById(employeeId);
int size=is.available();
byte[] image=new byte[size];
is.read(image);
ServletOutputStream out=response.getOutputStream();
out.write(image);
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
在此，调用业务类的getPicById方法得到图片数据的输入流。然后获取的输入流写到ServletOutputStream，这样可以在Servlet的输出端使用，即img的src中使用
getPicById代码如下：
public InputStream getPicById(int employeeId){
Connection conn=null;
PreparedStatement pstmt=null;
ResultSet rst=null;
InputStream is=null;
try{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
conn=DriverManager.getConnection("jdbc:jtds:sqlserver://localhost:1433/SampleDB","sa","");
String strSQL="SELECT pic FROM EmployeeInfo WHERE employeeId=?";
pstmt=conn.prepareStatement(strSQL);
pstmt.setInt(1, employeeId);
rst=pstmt.executeQuery();
if(rst.next()){
is=rst.getBinaryStream("pic");
return is;
}
return null;
}catch(ClassNotFoundException ex){
ex.printStackTrace();
return null;
}catch(SQLException ex){
ex.printStackTrace();
return null;
}finally{
try{
pstmt.close();
conn.close();
}catch(Exception ex){
}
}
}
注意粗体部分
好了，我们可以通过运行结果来进行验证，假设我们搜索名称为Mike的人员数据，那么这样：
点search按钮，运行结果如下：
好了，显示出了检索结果，不但包括人员的基本数据，保存到数据库中的图片数据也被读出并显示成图片。
代码只是利用jsp简单的进行体现，大家可以根据自己的需要进行改进。