Gradle构建Java Web应用：Servlet依赖与Tomcat插件

Gradle的官方tutorial介绍了构建Java Web应用的基本方法。不过在使用Servlet做上传的时候会碰到问题。这里分享下如何通过Servlet上传文件，以及如何使用Gradle来构建相应的Java Web工程。

参考原文：How to Build Web Scanning Application with Gradle

Servlet文件上传

使用Servlet文件上传，可以参考Oracle的官方文档The fileupload Example Application。这里需要注意的一个问题就是要接收multipart/form-data数据，在Servlet中必须申明：

@WebServlet(name = "FileUploadServlet", urlPatterns = {"/upload"}) @MultipartConfig

不然，getPart()会返回空。Servlet接收上传文件可以这样写：

/* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and open the template in the editor. */ package com.dynamsoft.upload; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.PrintWriter; import java.util.logging.Level; import java.util.logging.Logger; import javax.servlet.ServletException; import javax.servlet.annotation.MultipartConfig; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.Part; @WebServlet(name = "DWTUpload", urlPatterns = {"/DWTUpload"}) @MultipartConfig public class DWTUpload extends HttpServlet { private final static Logger LOGGER = Logger.getLogger(DWTUpload.class.getCanonicalName()); /** * Processes requests for both HTTP <code>GET</code> and <code>POST</code> * methods. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); // Create path components to save the file final Part filePart = request.getPart("RemoteFile"); final String fileName = getFileName(filePart); OutputStream out = null; InputStream filecontent = null; final PrintWriter writer = response.getWriter(); String realPath = getServletContext().getRealPath("/"); if (realPath == null) realPath = "f:\\web_upload"; // modify the default uploading dir accordingly String uploadPath = realPath + File.separator + "upload"; File uploadDir = new File(uploadPath); if (!uploadDir.exists()) uploadDir.mkdir(); try { out = new FileOutputStream(new File(uploadPath + File.separator + fileName)); filecontent = filePart.getInputStream(); int read = 0; final byte[] bytes = new byte[1024]; while ((read = filecontent.read(bytes)) != -1) { out.write(bytes, 0, read); } writer.println("New file " + fileName + " created at " + uploadPath); LOGGER.log(Level.INFO, "File{0}being uploaded to {1}", new Object[]{fileName, uploadPath}); } catch (FileNotFoundException fne) { writer.println("You either did not specify a file to upload or are " + "trying to upload a file to a protected or nonexistent " + "location."); writer.println("<br/> ERROR: " + fne.getMessage()); LOGGER.log(Level.SEVERE, "Problems during file upload. Error: {0}", new Object[]{fne.getMessage()}); } finally { if (out != null) { out.close(); } if (filecontent != null) { filecontent.close(); } if (writer != null) { writer.close(); } } } private String getFileName(final Part part) { final String partHeader = part.getHeader("content-disposition"); LOGGER.log(Level.INFO, "Part Header = {0}", partHeader); for (String content : part.getHeader("content-disposition").split(";")) { if (content.trim().startsWith("filename")) { return content.substring( content.indexOf('=') + 1).trim().replace("\"", ""); } } return null; } // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code."> /** * Handles the HTTP <code>GET</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Handles the HTTP <code>POST</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Returns a short description of the servlet. * * @return a String containing servlet description */ @Override public String getServletInfo() { return "Short description"; }// </editor-fold> }

Gradle构建Java Web工程

在使用Gradle构建这个Web工程的时候，如果按照官方文档，getPart这个方法是找不到的，用到的依赖可以换成：

dependencies { providedCompile "javax:javaee-api:6.0" }

另外一个问题就是使用jetty插件了，同样会失败。因为jetty不支持Servlet 3.0。官方论坛里有回复： Unable to use servlet 3.0 api in jetty plugin。替代方法可以使用Gradle Tomcat plugin 。在build.gradle文件中添加：

buildscript { repositories { jcenter() } dependencies { classpath 'com.bmuschko:gradle-tomcat-plugin:2.1' } } subprojects { apply plugin : "java" repositories { mavenCentral() } }

然后在子工程的build.gradle文件中添加tomcat插件：

apply plugin: "war" apply plugin: 'com.bmuschko.tomcat' dependencies { providedCompile "javax:javaee-api:6.0" def tomcatVersion = '7.0.59' tomcat "org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}", "org.apache.tomcat.embed:tomcat-embed-logging-juli:${tomcatVersion}", "org.apache.tomcat.embed:tomcat-embed-jasper:${tomcatVersion}" } tomcat { httpPort = 8080 httpsPort = 8091 enableSSL = true }

最后构建运行工程：

gradle build gradle tomcatRunWar

源码

https://github.com/Dynamsoft/Dynamic-Web-TWAIN/tree/master/samples/gradle

git clone https://github.com/Dynamsoft/Dynamic-Web-TWAIN.git