Java Servlet 例子 | Du Liu's Blog

Java Servlet ：是用Java编写的服务器端程序。其主要功能在于交互式地浏览和修改数据，生成动态Web内容。狭义的Servlet是指Java语言实现的一个接口，广义的Servlet是指任何实现了这个Servlet接口的类，一般情况下，人们将Servlet理解为后者。
Servlet运行于支持Java的应用服务器中。从实现上讲，Servlet可以响应任何类型的请求，但绝大多数情况下Servlet只用来扩展基于HTTP协议的Web服务器。

工作流程图：

一，使用xml配置的方式

1.HelloWrold HelloWorld.java

package com.devnp.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorld extends HttpServlet{

	/**
	 * @author duliu
	 */
	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest servletRequest, HttpServletResponse servletResponse)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		servletResponse.setContentType("text/html;charset=UTF-8");
		
		PrintWriter out = servletResponse.getWriter();
		 
	      // Write the response message, in an HTML page
	      try {
	         out.println("<!DOCTYPE html>");
	         out.println("<html><head>");
	         out.println("<meta http-equiv='Content-Type' content='text/html; charset=UTF-8'>");
	         out.println("<title>devnp.com</title></head>");
	         out.println("<body>");
	         out.println("


<h1>Hello, world! This is Servlet.</h1>



"); 
	         out.println("</body>");
	         out.println("</html>");
	      } finally {
	         out.close();
	      }
	}

	@Override
	protected void doPost(HttpServletRequest servletRequest, HttpServletResponse servletResponse)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		//doGet(servletRequest, servletResponse);
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		super.destroy();
	}

	@Override
	public void init(ServletConfig servletConfig) throws ServletException {
		// TODO Auto-generated method stub
		super.init(servletConfig);
	}
}

web.xml

<servlet>
	<servlet-name>HelloWorld</servlet-name>
	<servlet-class>com.devnp.servlet.HelloWorld</servlet-class>
</servlet>

<servlet-mapping>
	<servlet-name>HelloWorld</servlet-name>
	<url-pattern>/HelloWorld</url-pattern>
</servlet-mapping>

访问：http://localhost:7002/JavaServlet/HelloWorld

2.表单提交的例子
form_input.html

[code lang=”html”]

first_form_input

Name:

Languages

        <input type="checkbox" name="language" value="java" checked />Java
        <input type="checkbox" name="language" value="c" />C/C++
        <input type="checkbox" name="language" value="cs" />C#
     </fieldset>




     <input type="submit" value="提交" />
</form>


<em>InputServlet.java</em>

```java
package com.devnp.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class InputServlet extends HttpServlet{

	/**
	 * @author duliu
	 */
	private static final long serialVersionUID = 1L;
	
	@Override
	public void init(ServletConfig servletConfig) throws ServletException {
		// TODO Auto-generated method stub
		System.out.println("Servlet init.");
	}

	@Override
	protected void doPost(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
			throws ServletException, IOException {
		
		String nameStr = httpServletRequest.getParameter("name");
		
		String [] languages = httpServletRequest.getParameterValues("language");
		
		StringBuilder stringBuilder = new StringBuilder() ;
		if(languages != null){
			for (int i = 0; i < languages.length; i++) {
				String language = languages[i];
				
				stringBuilder.append(language + " ");
			}
		}
		
		httpServletResponse.setContentType("text/html;charset=UTF-8");
		
		PrintWriter out = httpServletResponse.getWriter();
		 
	      // Write the response message, in an HTML page
	      try {
	         out.println("<!DOCTYPE html>");
	         out.println("<html><head>");
	         out.println("<meta http-equiv='Content-Type' content='text/html; charset=UTF-8'>");
	         out.println("<title>first_form_input</title></head>");
	         out.println("<body>");
	         out.println("


<h1>Hello, " +nameStr + ", like " + stringBuilder.toString() + "</h1>



");  // says Hello
	         out.println("</body>");
	         out.println("</html>");
	      } finally {
	         out.close();  // Always close the output writer
	      }
	}
	

	@Override
	public void destroy() {
		System.out.println("Servlet destroy.");
	}
	
}

web.xml

<!-- input -->
  <servlet>
  	<servlet-name>InputServlet</servlet-name>
  	<servlet-class>com.devnp.servlet.InputServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
  	<servlet-name>InputServlet</servlet-name>
  	<url-pattern>/InputServlet</url-pattern>
  </servlet-mapping>

测试：http://localhost:7002/JavaServlet/form_input.html

提交

3.文件的上传
本例中，使用apache common-io,commom-upload 来完成文件的上传。
使用的版本在pom.xml的配置

<dependency>
	<groupId>commons-fileupload</groupId>
	<artifactId>commons-fileupload</artifactId>
	<version>1.2.2</version>
</dependency>
<dependency>
	<groupId>commons-io</groupId>
	<artifactId>commons-io</artifactId>
	<version>2.4</version>
</dependency>

fileUpload_form.html

[code lang=”html”]

FileUpload

    <input type="file" name="file" size="50" /> 


    <input type="submit" value="上传文件" />

</form>


<em>FileUploadServlet.java</em>

```java
package com.devnp.servlet;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class FileUploadServlet extends HttpServlet{

	/**
	 * @author duliu
	 */
	private static final long serialVersionUID = 1L;
	
	private static final String UPLOAD_DIRECTORY = "D:\\Person-Test" ;

	@Override
	protected void doPost(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		
		String message = null ;
		
		if(ServletFileUpload.isMultipartContent(httpServletRequest)){
            try {
                List<FileItem> multiparts = new ServletFileUpload(new DiskFileItemFactory()).parseRequest(httpServletRequest);
              
                for(FileItem item : multiparts){
                    if(!item.isFormField()){
                        String name = new File(item.getName()).getName();
                        item.write( new File(UPLOAD_DIRECTORY + File.separator + name));
                    }
                }
           
               //File uploaded successfully
                message = "File Uploaded Successfully";
            } catch (Exception ex) {
            	message = "File Upload Failed due to " + ex;
            }          
         
        }else{
        	message = "Sorry this Servlet only handles file upload request";
        }
    
		PrintWriter out = httpServletResponse.getWriter();
		out.print(message);
		
		out.close();
    }
	
}

web.xml

<!-- file upload -->
<servlet>
	<servlet-name>FileUploadServlet</servlet-name>
	<servlet-class>com.devnp.servlet.FileUploadServlet</servlet-class>
</servlet>

<servlet-mapping>
	<servlet-name>FileUploadServlet</servlet-name>
	<url-pattern>/FileUploadServlet</url-pattern>
</servlet-mapping>

测试：http://localhost:7002/JavaServlet/fileUpload_form.html

上传文件

二、注解的方式

1.HelloWolrd 在servlet 3.0之后引用注解的方式，减少xml配置的方式，轻松完成配置 HelloWorldAnnotation.java

package com.devnp.servlet3;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "HelloWorldAnnotation", urlPatterns = {"/HelloWorldAnnotation"})
public class HelloWorldAnnotation extends HttpServlet{

	/**
	 * @author duliu
	 */
	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		httpServletResponse.setContentType("text/html;charset=UTF-8");
		
		PrintWriter out = httpServletResponse.getWriter();
		 
	      // Write the response message, in an HTML page
	      try {
	         out.println("<!DOCTYPE html>");
	         out.println("<html><head>");
	         out.println("<meta http-equiv='Content-Type' content='text/html; charset=UTF-8'>");
	         out.println("<title>devnp.com</title></head>");
	         out.println("<body>");
	         out.println("


<h1>Hello, world! This is Servlet 3.0.</h1>



"); 
	         out.println("</body>");
	         out.println("</html>");
	      } finally {
	         out.close();
	      }
		
	}
}

访问：http://localhost:7002/JavaServlet/HelloWorldAnnotation

2.文件的上传
fileUpload_form2.html

[code lang=”html”]

FileUpload

    <input type="file" name="file" size="50" /> 


    <input type="submit" value="上传文件" />

</form>


<em>FileUploadServletAnnotation.java</em>

```java
package com.devnp.servlet3;

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 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 = "FileUploadServletAnnotation", urlPatterns = {"/FileUploadServletAnnotation"})
@MultipartConfig
public class FileUploadServletAnnotation extends HttpServlet{

	/**
	 * @author duliu
	 */
	private static final long serialVersionUID = 1L;

	@Override
	protected void doPost(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		
		Part filePart = httpServletRequest.getPart("file");
		
		String fileName = getFileName(filePart);
		
		OutputStream out = null;
	    InputStream filecontent = null;
	    PrintWriter writer = httpServletResponse.getWriter();

	    try {
	    	File file = new File("D:\\Person-Test" + File.separator + fileName);
	    	
	        out = new FileOutputStream(file);
	        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 " + "D:\\Person-Test");
	        
	    } 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("
 ERROR: " + fne.getMessage());

	    } finally {
	        if (out != null) {
	            out.close();
	        }
	        if (filecontent != null) {
	            filecontent.close();
	        }
	        if (writer != null) {
	            writer.close();
	        }
	    }
	}
	
	private String getFileName(Part part) {
	    for (String content : part.getHeader("Content-Disposition").split(";")) {
	        if (content.trim().startsWith("filename")) {
	            return content.substring(
	                    content.indexOf('=') + 1).trim().replace("\"", "");
	        }
	    }
	    
	    return null;
	}
}

测试：http://localhost:7002/JavaServlet/FileUploadServletAnnotation

上传文件

三、代码下载
JavaServlet.zip