[英]How to retrieve and display images from a database in a JSP page?
如何在 JSP 页面中从数据库中检索和显示图像?
让我们分步骤看看会发生什么:
<img>
元素。src
属性。src
属性需要指向有效的http://
URL,因此不是本地磁盘文件系统路径file://
,因为当服务器和客户端在物理上不同的机器上运行时,这将永远无法工作。http://example.com/context/images/foo.png
)或请求参数(例如http://example.com/context/images?id=1
)。/images/*
,以便您可以在特定 URL 上执行一些 Java 代码。byte[]
或InputStream
从 DB 中获取, JDBC API为此提供ResultSet#getBytes()
和ResultSet#getBinaryStream()
, JPA API为此提供@Lob
。byte[]
或InputStream
写入响应的OutputStream
。Content-Type
响应头。 您可以根据图像文件扩展名通过ServletContext#getMimeType()
获得正确的图像文件扩展名,您可以通过web.xml
<mime-mapping>
扩展和/或覆盖。应该是这样。 它几乎自己编写代码。 让我们从 HTML 开始(在JSP 中):
<img src="${pageContext.request.contextPath}/images/foo.png">
<img src="${pageContext.request.contextPath}/images/bar.png">
<img src="${pageContext.request.contextPath}/images/baz.png">
如有必要,您还可以在使用JSTL进行迭代时使用EL动态设置src
:
<c:forEach items="${imagenames}" var="imagename">
<img src="${pageContext.request.contextPath}/images/${imagename}">
</c:forEach>
然后定义/创建一个servlet ,它侦听/images/*
URL 模式上的 GET 请求,下面的示例使用普通的 JDBC 进行作业:
@WebServlet("/images/*")
public class ImageServlet extends HttpServlet {
// content=blob, name=varchar(255) UNIQUE.
private static final String SQL_FIND = "SELECT content FROM Image WHERE name = ?";
@Resource(name="jdbc/yourDB") // For Tomcat, define as <Resource> in context.xml and declare as <resource-ref> in web.xml.
private DataSource dataSource;
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String imageName = request.getPathInfo().substring(1); // Returns "foo.png".
try (Connection connection = dataSource.getConnection(); PreparedStatement statement = connection.prepareStatement(SQL_FIND)) {
statement.setString(1, imageName);
try (ResultSet resultSet = statement.executeQuery()) {
if (resultSet.next()) {
byte[] content = resultSet.getBytes("content");
response.setContentType(getServletContext().getMimeType(imageName));
response.setContentLength(content.length);
response.getOutputStream().write(content);
} else {
response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
}
}
} catch (SQLException e) {
throw new ServletException("Something failed at SQL/DB level.", e);
}
}
}
就是这样。 如果您担心 HEAD 和缓存标头并正确响应这些请求,请将此抽象模板用于静态资源 servlet 。
我建议您将其视为两个问题。 有几个问题和答案与两者相关。
如何从 MySQL 加载 blob
参见例如检索存储为 blob 的图像
如何动态显示图像
参见例如动态显示缩略图
如果未显示,请尝试刷新并关闭输出流。 Blob image = rs.getBlob(ImageColName);
InputStream in = image.getBinaryStream();
// 将 blob 输出到 HttpServletResponse response.setContentType("image/jpeg");
BufferedOutputStream o = new BufferedOutputStream(response.getOutputStream());
byte by[] = new byte[32768];
int index = in.read(by, 0, 32768);
while (index != -1) {
o.write(by, 0, index);
index = in.read(by, 0, 32768);
}
o.flush();
o.close();
我已经使用 Oracle 数据库在 JSP 中编写和配置了代码。 希望它会有所帮助。
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.http.HttpSession;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class displayfetchimage
*/
@WebServlet("/displayfetchimage")
public class displayfetchimage extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public displayfetchimage() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
Statement stmt = null;
String sql = null;
BufferedInputStream bin = null;
BufferedOutputStream bout = null;
InputStream in = null;
response.setContentType("image/jpeg");
ServletOutputStream out;
out = response.getOutputStream();
Connection conn = employee.DbConnection.getDatabaseConnection();
HttpSession session = (HttpSession) request.getSession();
String ID = session.getAttribute("userId").toString().toLowerCase();
try {
stmt = conn.createStatement();
sql = "select user_image from employee_data WHERE username='" + ID + "' and rownum<=1";
ResultSet result = stmt.executeQuery(sql);
if (result.next()) {
in = result.getBinaryStream(1);// Since my data was in first column of table.
}
bin = new BufferedInputStream(in);
bout = new BufferedOutputStream(out);
int ch = 0;
while ((ch = bin.read()) != -1) {
bout.write(ch);
}
} catch (SQLException ex) {
Logger.getLogger(displayfetchimage.class.getName()).log(Level.SEVERE, null, ex);
} finally {
try {
if (bin != null)
bin.close();
if (in != null)
in.close();
if (bout != null)
bout.close();
if (out != null)
out.close();
if (conn != null)
conn.close();
} catch (IOException | SQLException ex) {
System.out.println("Error : " + ex.getMessage());
}
}
}
// response.getWriter().append("Served at: ").append(request.getContextPath());
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Statement stmt = null;
String sql = null;
BufferedInputStream bin = null;
BufferedOutputStream bout = null;
InputStream in = null;
response.setContentType("image/jpeg");
ServletOutputStream out;
out = response.getOutputStream();
Connection conn = employee.DbConnection.getDatabaseConnection();
HttpSession session = (HttpSession) request.getSession();
String ID = session.getAttribute("userId").toString().toLowerCase();
try {
stmt = conn.createStatement();
sql = "select user_image from employee_data WHERE username='" + ID + "' and rownum<=1";
ResultSet result = stmt.executeQuery(sql);
if (result.next()) {
in = result.getBinaryStream(1);
}
bin = new BufferedInputStream(in);
bout = new BufferedOutputStream(out);
int ch = 0;
while ((ch = bin.read()) != -1) {
bout.write(ch);
}
} catch (SQLException ex) {
Logger.getLogger(displayfetchimage.class.getName()).log(Level.SEVERE, null, ex);
} finally {
try {
if (bin != null)
bin.close();
if (in != null)
in.close();
if (bout != null)
bout.close();
if (out != null)
out.close();
if (conn != null)
conn.close();
} catch (IOException | SQLException ex) {
System.out.println("Error : " + ex.getMessage());
}
}
}
}
您还可以创建用于显示图像的自定义标签。
1)创建自定义标签java类和tld文件。
2) 编写逻辑来显示图像,例如通过 Base64 将 byte[] 转换为字符串。
因此,无论您是在单个 jsp 页面中仅显示一张图像还是多张图像,它都会用于每个图像。
我使用了 SQL SERVER 数据库,所以答案的代码是一致的。 你所要做的就是在你的 jsp 页面中包含一个<img>
标签,并像这样从它的 src 属性调用一个 servlet
<img width="200" height="180" src="DisplayImage?ID=1">
这里1是数据库中图像的唯一ID,ID是一个变量。 我们在 servlet 中接收这个变量的值。 在 servlet 代码中,我们从表中的正确列中获取二进制流输入。 那就是你的图像存储在哪一列。 在我的代码中,我使用了第三列,因为我的图像在第三列中存储为二进制数据。 从表中检索输入流数据后,我们在输出流中读取其内容,以便将其写入屏幕。 就这个
import java.io.*;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.*;
import javax.servlet.http.*;
import model.ConnectionManager;
public class DisplayImage extends HttpServlet {
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws IOException
{
Statement stmt=null;
String sql=null;
BufferedInputStream bin=null;
BufferedOutputStream bout=null;
InputStream in =null;
response.setContentType("image/jpeg");
ServletOutputStream out;
out = response.getOutputStream();
Connection conn = ConnectionManager.getConnection();
int ID = Integer.parseInt(request.getParameter("ID"));
try {
stmt = conn.createStatement();
sql = "SELECT * FROM IMAGETABLE WHERE ID="+ID+"";
ResultSet result = stmt.executeQuery(sql);
if(result.next()){
in=result.getBinaryStream(3);//Since my data was in third column of table.
}
bin = new BufferedInputStream(in);
bout = new BufferedOutputStream(out);
int ch=0;
while((ch=bin.read())!=-1)
{
bout.write(ch);
}
} catch (SQLException ex) {
Logger.getLogger(DisplayImage.class.getName()).log(Level.SEVERE, null, ex);
}finally{
try{
if(bin!=null)bin.close();
if(in!=null)in.close();
if(bout!=null)bout.close();
if(out!=null)out.close();
if(conn!=null)conn.close();
}catch(IOException | SQLException ex){
System.out.println("Error : "+ex.getMessage());
}
}
}
}
在执行您的 jsp 或 html 文件后,您将在屏幕上看到图像。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.