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使用HttpClient实现文件的上传下载方法

程序员文章站 2024-03-09 08:50:35
1 http http 协议可能是现在 internet 上使用得最多、最重要的协议了,越来越多的 java 应用程序需要直接通过 http 协议来访问网络资源。 虽然...

1 http

http 协议可能是现在 internet 上使用得最多、最重要的协议了,越来越多的 java 应用程序需要直接通过 http 协议来访问网络资源。

虽然在 jdk 的 java.net 包中已经提供了访问 http 协议的基本功能,但是对于大部分应用程序来说,jdk 库本身提供的功能还不够丰富和灵活。httpclient 用来提供高效的、最新的、功能丰富的支持 http 协议的客户端编程工具包,并且它支持 http 协议最新的版本和建议。

一般的情况下我们都是使用chrome或者其他浏览器来访问一个web服务器,用来浏览页面查看信息或者提交一些数据、文件上传下载等等。所访问的这些页面有的仅仅是一些普通的页面,有的需要用户登录后方可使用,或者需要认证以及是一些通过加密方式传输,例如https。目前我们使用的浏览器处理这些情况都不会构成问题。但是一旦我们有需求不通过浏览器来访问服务器的资源呢?那该怎么办呢?

下面以本地客户端发起文件的上传、下载为例做个小demo。httpclient有两种形式,一种是org.apache.http下的,一种是org.apache.commons.httpclient.httpclient。

2 文件上传

文件上传可以使用两种方式实现,一种是postmethod方式,一种是httppost方式。两者的处理大同小异。postmethod是使用filebody将文件包装流包装起来,httppost是使用filepart将文件流包装起来。在传递文件流给服务端的时候,都可以同时传递其他的参数。

2.1 客户端处理

2.1.1 postmethod方式

将文件封装到filepart中,放入part数组,同时,其他参数可以放入stringpart中,这里没有写,只是单纯的将参数以setparameter的方式进行设置。此处的httpclient是org.apache.commons.httpclient.httpclient。

 

public void upload(string localfile){
    file file = new file(localfile);
    postmethod filepost = new postmethod(url_str);
    httpclient client = new httpclient();
    
    try {
      // 通过以下方法可以模拟页面参数提交
      filepost.setparameter("username", username);
      filepost.setparameter("passwd", passwd);

      part[] parts = { new filepart(file.getname(), file) };
      filepost.setrequestentity(new multipartrequestentity(parts, filepost.getparams()));
      
      client.gethttpconnectionmanager().getparams().setconnectiontimeout(5000);
      
      int status = client.executemethod(filepost);
      if (status == httpstatus.sc_ok) {
        system.out.println("上传成功");
      } else {
        system.out.println("上传失败");
      }
    } catch (exception ex) {
      ex.printstacktrace();
    } finally {
      filepost.releaseconnection();
    }
  }

记得搞完之后,要通过releaseconnection释放连接。

2.1.2 httppost方式

这种方式,与上面类似,只不过变成了filebody。上面的part数组在这里对应httpentity。此处的httpclient是org.apache.http.client.methods下的。

public void upload(string localfile){
    closeablehttpclient httpclient = null;
    closeablehttpresponse response = null;
    try {
      httpclient = httpclients.createdefault();
      
      // 把一个普通参数和文件上传给下面这个地址 是一个servlet
      httppost httppost = new httppost(url_str);
      
      // 把文件转换成流对象filebody
      filebody bin = new filebody(new file(localfile));

      stringbody username = new stringbody("scott", contenttype.create(
          "text/plain", consts.utf_8));
      stringbody password = new stringbody("123456", contenttype.create(
          "text/plain", consts.utf_8));

      httpentity reqentity = multipartentitybuilder.create()
          // 相当于<input type="file" name="file"/>
          .addpart("file", bin)
          
          // 相当于<input type="text" name="username" value=username>
          .addpart("username", username)
          .addpart("pass", password)
          .build();

      httppost.setentity(reqentity);

      // 发起请求 并返回请求的响应
      response = httpclient.execute(httppost);
      
      system.out.println("the response value of token:" + response.getfirstheader("token"));
        
      // 获取响应对象
      httpentity resentity = response.getentity();
      if (resentity != null) {
        // 打印响应长度
        system.out.println("response content length: " + resentity.getcontentlength());
        // 打印响应内容
        system.out.println(entityutils.tostring(resentity, charset.forname("utf-8")));
      }
      
      // 销毁
      entityutils.consume(resentity);
    }catch (exception e){
      e.printstacktrace();
    }finally {
      try {
        if(response != null){
          response.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
      
      try {
        if(httpclient != null){
          httpclient.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
    }
  }

2.2 服务端处理

 无论客户端是哪种上传方式,服务端的处理都是一样的。在通过httpservletrequest获得参数之后,把得到的item进行分类,分为普通的表单和file表单。

 通过servletfileupload 可以设置上传文件的大小及编码格式等。

 总之,服务端的处理是把得到的参数当做html表单进行处理的。  

public void processupload(httpservletrequest request, httpservletresponse response){
    file uploadfile = new file(uploadpath);
    if (!uploadfile.exists()) {
      uploadfile.mkdirs();
    }

    system.out.println("come on, baby .......");
    
    request.setcharacterencoding("utf-8"); 
    response.setcharacterencoding("utf-8"); 
     
    //检测是不是存在上传文件 
    boolean ismultipart = servletfileupload.ismultipartcontent(request); 
     
    if(ismultipart){ 
      diskfileitemfactory factory = new diskfileitemfactory(); 
      
      //指定在内存中缓存数据大小,单位为byte,这里设为1mb 
      factory.setsizethreshold(1024*1024); 
      
      //设置一旦文件大小超过getsizethreshold()的值时数据存放在硬盘的目录  
      factory.setrepository(new file("d:\\temp")); 
      
      // create a new file upload handler 
      servletfileupload upload = new servletfileupload(factory); 
      
      // 指定单个上传文件的最大尺寸,单位:字节,这里设为50mb  
      upload.setfilesizemax(50 * 1024 * 1024);  
      
      //指定一次上传多个文件的总尺寸,单位:字节,这里设为50mb 
      upload.setsizemax(50 * 1024 * 1024);   
      upload.setheaderencoding("utf-8");
       
      list<fileitem> items = null; 
       
      try { 
        // 解析request请求 
        items = upload.parserequest(request); 
      } catch (fileuploadexception e) { 
        e.printstacktrace(); 
      } 
      
      if(items!=null){ 
        //解析表单项目 
        iterator<fileitem> iter = items.iterator(); 
        while (iter.hasnext()) { 
          fileitem item = iter.next(); 
          
          //如果是普通表单属性 
          if (item.isformfield()) { 
            //相当于input的name属性  <input type="text" name="content"> 
            string name = item.getfieldname();
            
            //input的value属性 
            string value = item.getstring();
            
            system.out.println("属性:" + name + " 属性值:" + value); 
          } 
          //如果是上传文件 
          else { 
            //属性名 
            string fieldname = item.getfieldname(); 
            
            //上传文件路径 
            string filename = item.getname(); 
            filename = filename.substring(filename.lastindexof("/") + 1);// 获得上传文件的文件名 
            
            try { 
              item.write(new file(uploadpath, filename)); 
            } catch (exception e) { 
              e.printstacktrace(); 
            } 
          } 
        } 
      } 
    } 
    
    response.addheader("token", "hello");
  }

服务端在处理之后,可以在header中设置返回给客户端的简单信息。如果返回客户端是一个流的话,流的大小必须提前设置!

response.setcontentlength((int) file.length());

3 文件下载

文件的下载可以使用httpclient的getmethod实现,还可以使用httpget方式、原始的httpurlconnection方式。

3.1 客户端处理

3.1.1 getmethod方式

此处的httpclient是org.apache.commons.httpclient.httpclient。

public void download(string remotefilename, string localfilename) {
    httpclient client = new httpclient();
    getmethod get = null;
    fileoutputstream output = null;
    
    try {
      get = new getmethod(url_str);
      get.setrequestheader("username", username);
      get.setrequestheader("passwd", passwd);
      get.setrequestheader("filename", remotefilename);

      int i = client.executemethod(get);

      if (success == i) {
        system.out.println("the response value of token:" + get.getresponseheader("token"));

        file storefile = new file(localfilename);
        output = new fileoutputstream(storefile);
        
        // 得到网络资源的字节数组,并写入文件
        output.write(get.getresponsebody());
      } else {
        system.out.println("download file occurs exception, the error code is :" + i);
      }
    } catch (exception e) {
      e.printstacktrace();
    } finally {
      try {
        if(output != null){
          output.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
      
      get.releaseconnection();
      client.gethttpconnectionmanager().closeidleconnections(0);
    }
  }

3.1.2 httpget方式

此处的httpclient是org.apache.http.client.methods下的。

public void download(string remotefilename, string localfilename) {
    defaulthttpclient httpclient = new defaulthttpclient();
    outputstream out = null;
    inputstream in = null;
    
    try {
      httpget httpget = new httpget(url_str);

      httpget.addheader("username", username);
      httpget.addheader("passwd", passwd);
      httpget.addheader("filename", remotefilename);

      httpresponse httpresponse = httpclient.execute(httpget);
      httpentity entity = httpresponse.getentity();
      in = entity.getcontent();

      long length = entity.getcontentlength();
      if (length <= 0) {
        system.out.println("下载文件不存在!");
        return;
      }

      system.out.println("the response value of token:" + httpresponse.getfirstheader("token"));

      file file = new file(localfilename);
      if(!file.exists()){
        file.createnewfile();
      }
      
      out = new fileoutputstream(file); 
      byte[] buffer = new byte[4096];
      int readlength = 0;
      while ((readlength=in.read(buffer)) > 0) {
        byte[] bytes = new byte[readlength];
        system.arraycopy(buffer, 0, bytes, 0, readlength);
        out.write(bytes);
      }
      
      out.flush();
      
    } catch (ioexception e) {
      e.printstacktrace();
    } catch (exception e) {
      e.printstacktrace();
    }finally{
      try {
        if(in != null){
          in.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
      
      try {
        if(out != null){
          out.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
    }
  }

3.1.3 httpurlconnection方式

public void download3(string remotefilename, string localfilename) {
    fileoutputstream out = null;
    inputstream in = null;
    
    try{
      url url = new url(url_str);
      urlconnection urlconnection = url.openconnection();
      httpurlconnection httpurlconnection = (httpurlconnection) urlconnection;
      
      // true -- will setting parameters
      httpurlconnection.setdooutput(true);
      // true--will allow read in from
      httpurlconnection.setdoinput(true);
      // will not use caches
      httpurlconnection.setusecaches(false);
      // setting serialized
      httpurlconnection.setrequestproperty("content-type", "application/x-java-serialized-object");
      // default is get            
      httpurlconnection.setrequestmethod("post");
      httpurlconnection.setrequestproperty("connection", "keep-alive");
      httpurlconnection.setrequestproperty("charsert", "utf-8");
      // 1 min
      httpurlconnection.setconnecttimeout(60000);
      // 1 min
      httpurlconnection.setreadtimeout(60000);

      httpurlconnection.addrequestproperty("username", username);
      httpurlconnection.addrequestproperty("passwd", passwd);
      httpurlconnection.addrequestproperty("filename", remotefilename);

      // connect to server (tcp)
      httpurlconnection.connect();

      in = httpurlconnection.getinputstream();// send request to
                                // server
      file file = new file(localfilename);
      if(!file.exists()){
        file.createnewfile();
      }

      out = new fileoutputstream(file); 
      byte[] buffer = new byte[4096];
      int readlength = 0;
      while ((readlength=in.read(buffer)) > 0) {
        byte[] bytes = new byte[readlength];
        system.arraycopy(buffer, 0, bytes, 0, readlength);
        out.write(bytes);
      }
      
      out.flush();
    }catch(exception e){
      e.printstacktrace();
    }finally{
      try {
        if(in != null){
          in.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
      
      try {
        if(out != null){
          out.close();
        }
      } catch (ioexception e) {
        e.printstacktrace();
      }
    }
  }

3.2 服务端处理

尽管客户端的处理方式不同,但是服务端是一样的。

public void processdownload(httpservletrequest request, httpservletresponse response){
    int buffer_size = 4096;
    inputstream in = null;
    outputstream out = null;
    
    system.out.println("come on, baby .......");
    
    try{
      request.setcharacterencoding("utf-8"); 
      response.setcharacterencoding("utf-8"); 
      response.setcontenttype("application/octet-stream");
      
      string username = request.getheader("username");
      string passwd = request.getheader("passwd");
      string filename = request.getheader("filename");
      
      system.out.println("username:" + username);
      system.out.println("passwd:" + passwd);
      system.out.println("filename:" + filename);
      
      //可以根据传递来的username和passwd做进一步处理,比如验证请求是否合法等       
      file file = new file(downloadpath + "\\" + filename);
      response.setcontentlength((int) file.length());
      response.setheader("accept-ranges", "bytes");
      
      int readlength = 0;
      
      in = new bufferedinputstream(new fileinputstream(file), buffer_size);
      out = new bufferedoutputstream(response.getoutputstream());
      
      byte[] buffer = new byte[buffer_size];
      while ((readlength=in.read(buffer)) > 0) {
        byte[] bytes = new byte[readlength];
        system.arraycopy(buffer, 0, bytes, 0, readlength);
        out.write(bytes);
      }
      
      out.flush();
      
      response.addheader("token", "hello 1");
       
    }catch(exception e){
      e.printstacktrace();
       response.addheader("token", "hello 2");
    }finally {
      if (in != null) {
        try {
          in.close();
        } catch (ioexception e) {
        }
      }
      if (out != null) {
        try {
          out.close();
        } catch (ioexception e) {
        }
      }
    }
  }

4 小结

httpclient最基本的功能就是执行http方法。一个http方法的执行涉及到一个或者多个http请求/http响应的交互,通常这个过程都会自动被httpclient处理,对用户透明。用户只需要提供http请求对象,httpclient就会将http请求发送给目标服务器,并且接收服务器的响应,如果http请求执行不成功,httpclient就会抛出异常。所以在写代码的时候注意finally的处理。

所有的http请求都有一个请求列(request line),包括方法名、请求的uri和http版本号。httpclient支持http/1.1这个版本定义的所有http方法:get,head,post,put,delete,trace和options。上面的上传用到了post,下载是get。

目前来说,使用org.apache.commons.httpclient.httpclient多一些。看自己了~

以上就是小编为大家带来的使用httpclient实现文件的上传下载方法全部内容了,希望大家多多支持~