[英]How to retrieve and display images from a database in a JSP page?
如何在 JSP 頁面中從數據庫中檢索和顯示圖像?
讓我們分步驟看看會發生什么:
<img>
元素。src
屬性。src
屬性需要指向有效的http://
URL,因此不是本地磁盤文件系統路徑file://
,因為當服務器和客戶端在物理上不同的機器上運行時,這將永遠無法工作。http://example.com/context/images/foo.png
)或請求參數(例如http://example.com/context/images?id=1
)。/images/*
,以便您可以在特定 URL 上執行一些 Java 代碼。byte[]
或InputStream
從 DB 中獲取, JDBC API為此提供ResultSet#getBytes()
和ResultSet#getBinaryStream()
, JPA API為此提供@Lob
。byte[]
或InputStream
寫入響應的OutputStream
。Content-Type
響應頭。 您可以根據圖像文件擴展名通過ServletContext#getMimeType()
獲得正確的圖像文件擴展名,您可以通過web.xml
<mime-mapping>
擴展和/或覆蓋。應該是這樣。 它幾乎自己編寫代碼。 讓我們從 HTML 開始(在JSP 中):
<img src="${pageContext.request.contextPath}/images/foo.png">
<img src="${pageContext.request.contextPath}/images/bar.png">
<img src="${pageContext.request.contextPath}/images/baz.png">
如有必要,您還可以在使用JSTL進行迭代時使用EL動態設置src
:
<c:forEach items="${imagenames}" var="imagename">
<img src="${pageContext.request.contextPath}/images/${imagename}">
</c:forEach>
然后定義/創建一個servlet ,它偵聽/images/*
URL 模式上的 GET 請求,下面的示例使用普通的 JDBC 進行作業:
@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);
}
}
}
就是這樣。 如果您擔心 HEAD 和緩存標頭並正確響應這些請求,請將此抽象模板用於靜態資源 servlet 。
我建議您將其視為兩個問題。 有幾個問題和答案與兩者相關。
如何從 MySQL 加載 blob
參見例如檢索存儲為 blob 的圖像
如何動態顯示圖像
參見例如動態顯示縮略圖
如果未顯示,請嘗試刷新並關閉輸出流。 Blob image = rs.getBlob(ImageColName);
InputStream in = image.getBinaryStream();
// 將 blob 輸出到 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();
我已經使用 Oracle 數據庫在 JSP 中編寫和配置了代碼。 希望它會有所幫助。
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());
}
}
}
}
您還可以創建用於顯示圖像的自定義標簽。
1)創建自定義標簽java類和tld文件。
2) 編寫邏輯來顯示圖像,例如通過 Base64 將 byte[] 轉換為字符串。
因此,無論您是在單個 jsp 頁面中僅顯示一張圖像還是多張圖像,它都會用於每個圖像。
我使用了 SQL SERVER 數據庫,所以答案的代碼是一致的。 你所要做的就是在你的 jsp 頁面中包含一個<img>
標簽,並像這樣從它的 src 屬性調用一個 servlet
<img width="200" height="180" src="DisplayImage?ID=1">
這里1是數據庫中圖像的唯一ID,ID是一個變量。 我們在 servlet 中接收這個變量的值。 在 servlet 代碼中,我們從表中的正確列中獲取二進制流輸入。 那就是你的圖像存儲在哪一列。 在我的代碼中,我使用了第三列,因為我的圖像在第三列中存儲為二進制數據。 從表中檢索輸入流數據后,我們在輸出流中讀取其內容,以便將其寫入屏幕。 就這個
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());
}
}
}
}
在執行您的 jsp 或 html 文件后,您將在屏幕上看到圖像。
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