我正在开发一个Spring-MVC应用程序，我必须使用图像上传来存储数据库中的图像。我试图通过互联网上的例子，但我的整体观察是有一些关于上传类型和谁管理它的论点。不过，我正在从HTML上传图像，将其作为OID保存在数据库中，使用带@Lob的字节数组进行保存。我使用时无法看到图像预览：
我将发布我如何实现它的代码，请告诉我什么是错的。
图片预览的HTML代码：
<img src="${product.productimage}" width="100" height="100"/>
当我在服务中使用product.getImage（）。toString时，我会通过'B [jlkisf12'获得奇怪的字符，但只有12-13个，我想这就是路径。
实体：
@Column(name = "productimage")
byte[] productimage; // With getters and setters
JSP文件：
<c:url var="add" value="/product/add"></c:url>
<form:form action="${add}" commandName="product">
<table>
<c:if test="${!empty product.productname}">
<tr>
<td>
<form:label path="productid">
<spring:message text="productid"/>
</form:label>
</td>
<td>
<form:input path="productid" readonly="true" size="8" disabled="true" />
<form:hidden path="productid" />
</td>
</tr>
</c:if>
<tr>
<td>
<form:label path="productname">
<spring:message text="productname:"/>
</form:label>
</td>
<td>
<form:input path="productname"/>
</td>
</tr>
<tr>
<td>
<form:label path="productdescription">
<spring:message text="productdescription"/>
</form:label>
</td>
<td>
<form:input path="productdescription"/>
</td>
</tr>
<tr>
<td>
<form:label path="productcondition">
<spring:message text="productcondition"/>
</form:label>
</td>
<td>
<form:input path="productcondition"/>
</td>
</tr>
<tr>
<td>
<form:label path="productage">
<spring:message text="productage"/>
</form:label>
</td>
<td>
<form:input path="productage" />
</td>
</tr>
<tr>
<td>
<form:label path="productean">
<spring:message text="productean"/>
</form:label>
</td>
<td>
<form:input path="productean" />
</td>
</tr>
<tr>
<td>
<form:label path="productisbn">
<spring:message text="productisbn"/>
</form:label>
</td>
<td>
<form:input path="productisbn" />
</td>
</tr>
<tr>
<td>
<form:label path="ordernumber">
<spring:message text="ordernumber"/>
</form:label>
</td>
<td>
<form:input path="ordernumber" />
</td>
</tr>
<tr>
<td>
<form:label path="productimage">
<spring:message text="productimage"/>
</form:label>
</td>
<td>
<form:input type="file" path="productimage" />
</td>
</tr>
</table>
<tr>
<td colspan="2">
<c:if test="${!empty product.productname}">
<input type="submit"
value="<spring:message text="Edit Product"/>" />
</c:if>
<c:if test="${empty product.productname}">
<input type="submit"
value="<spring:message text="Add Product"/>" />
</c:if>
</td>
</tr>
</form:form>
<br>
<h3>Product List</h3>
<c:if test="${!empty listProducts}">
<table class="tg">
<tr>
<th width="80">Product ID</th>
<th width="80">Product image</th>
<th width="120">Product name</th>
<th width="120">Product description</th>
<th width="120">Product condition</th>
<th width="120">Product age</th>
<th width="120">Product EAN</th>
<th width="120">Product ISBN</th>
<th width="120">Product ordernumber</th>
<th width="120">Product owners id</th>
<th width="60">Edit</th>
<th width="60">Delete</th>
</tr>
<c:forEach items="${listProducts}" var="product">
<tr>
<td>${product.productid}</td>
<td>${product.productimage} </td>
<td>${product.productname}</td>
<td>${product.productdescription}</td>
<td>${product.productcondition}</td>
<td>${product.productage}</td>
<td>${product.productean}</td>
<td>${product.productisbn}</td>
<td>${product.ordernumber}</td>
<td>${product.user1id}</td>
<img src="${image}" width="100" height="100"/> //image not found
<td><a href="<c:url value='/editproduct/${product.productid}' />" >Edit Product</a></td>
<td><a href="<c:url value='/removeproduct/${product.productid}' />" >Delete Product</a></td>
</tr>
<img src="${product.saveimage}" height="100" width="100">
</c:forEach>
</table>
</c:if>
控制器：
@RequestMapping(value="/product/show",method= RequestMethod.GET)
public String listProducts(@ModelAttribute("product") ProductBasic productBasic,Model model) {
User user = userService.getCurrentlyAuthenticatedUser();
model.addAttribute("product", new ProductBasic());
model.addAttribute("listProducts",this.productBasicService.listProduct(user));
BASE64Encoder base64Encoder = new BASE64Encoder();
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("data:image/png;base64,");
stringBuilder.append(base64Encoder.encode(productBasic.getProductimage()));
String image = stringBuilder.toString();
model.addAttribute("saveimage",image);
return "product";
}
@RequestMapping(value="/product/add")
public String addProduct(@ModelAttribute("product") ProductBasic productBasic,Model model){
User user = userService.getCurrentlyAuthenticatedUser();
model.addAttribute("product", new ProductBasic());
productBasicService.addProduct(user,productBasic);
return "redirect:/product/show";
}
@RequestMapping("/removeproduct/{id}")
public String removeProduct(@PathVariable("id") int productid,Model model) {
User user = userService.getCurrentlyAuthenticatedUser();
model.addAttribute("listProducts",this.productBasicService.listProduct(user));
this.productBasicService.removeProduct(productid,user);
return "redirect:/product/show";
}
@RequestMapping("/editproduct/{id}")
public String updateProduct(@ModelAttribute("product") ProductBasic productBasic,@PathVariable("id") Integer id,Model model){
User user = userService.getCurrentlyAuthenticatedUser();
model.addAttribute("product", this.productBasicService.getProductById(id));
model.addAttribute("listProducts",this.productBasicService.listProduct(user));
return "product";
}
的NullPointerException：
java.lang.NullPointerException
java.io.ByteArrayInputStream.<init>(ByteArrayInputStream.java:106)
sun.misc.CharacterEncoder.encode(CharacterEncoder.java:188)
com.WirTauschen.UserController.listProducts(UserController.java:67)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
我做错了什么？请告诉我。
答案 0 :(得分：2)
在您的控制器或方法中添加下面的图像代码
BASE64Encoder base64Encoder = new BASE64Encoder();
StringBuilder imageString = new StringBuilder();
imageString.append("data:image/png;base64,");
imageString.append(base64Encoder.encode(bytes)); //bytes will be image byte[] come from DB
String image = imageString.toString();
modelView.put("imagetoDisplay",image);// put in your model object for using in your JSP
在JSP中
<img src="${imagetoDisplay}" width="100" height="100"/>