在web项目中一般常见的五种返回形式：
- 返回页面，使用模板引擎，spring boot推荐使用thymeleaf，类似的还有freemarker等。
- 返回字符串（json），一般用于完全的前后端分离开发，或者提供接口服务。
- 返回重定向，一些较少的业务需求。
- 转发，一些较少的业务需求。
- 流输出，常用于下载文件。
方法前代码：
package cn.mario.springboot.controller;import org.json.JSONException;
import org.json.JSONObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.thymeleaf.util.StringUtils;import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;/*** @PackageName cn.mario.springboot.controller* @ClassName TestController* @Author BenMario* @Date 2018/5/23 3:16* @Description test controoler* @Version 1.0**/@Controller
public class TestController {private Logger logger = LoggerFactory.getLogger(TestController.class);
1.返回页面：使用spring boot 推荐的thymeleaf，默认模板路径：resources/templates/*.html
代码：
/*** retrun page* @param request HttpServletRequest* @param response HttpServletResponse* @return test page*/@RequestMapping(value = "/testReturnPage")public String testReturnPage(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testReturnPage function");System.out.println("into testReturnPage function");return "test";}
2.1返回普通字符串
代码：
/*** retrun general string* @param request HttpServletRequest* @param response HttpServletResponse* @return str*/@ResponseBody@RequestMapping(value = "/testReturnString")public String testReturnString(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testReturnString function");System.out.println("into testReturnString function");String str = "RETRUN STRING";return str;}
2.2返回json字符串
代码：
/*** retrun json string* @param request HttpServletRequest* @param response HttpServletResponse* @return JSONObject to string*/@ResponseBody@RequestMapping(value = "/testReturnJSONObject")public String testReturnJSONObject(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testReturnJSONObject function");System.out.println("into testReturnJSONObject functioin");JSONObject jsonObject = new JSONObject();try {jsonObject.put("name_1", StringUtils.toString(1));jsonObject.put("name_2", 1);} catch (JSONException e) {e.printStackTrace();}return jsonObject.toString();}
3.1.1利用关键字“redirect”跨web服务重定向
代码：
/*** retrun cross web project redirect* @param request HttpServletRequest* @param response HttpServletResponse* @return redirect cross web project*/@RequestMapping(value = "/testRedirect_1")public String testRedirect_1(HttpServletRequest request, HttpServletResponse response) {logger.debug("inot testRedirect_1 function");System.out.println("into testRedirect_1 function");String url = "http://www.baidu.com";return "redirect:" + url;}
3.1.2利用关键字“redirect”同web服务重定向
代码：
/*** retrun same web project redirect* @param request HttpServletRequest* @param response HttpServletResponse* @return redirect same web project*/@RequestMapping(value = "/testRedirect_2")public String testRedirect_2(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testRedirect_2 function");System.out.println("into testRedirect_2 function");String url = "/testRedirect_1";return "redirect:" + url;}
3.2.1利用HttpServletRespons对象跨web服务重定向
代码：
/*** retrun cross web project redirect* @param request HttpServletRequest* @param response HttpServletResponse* @return redirect cross web project*/@RequestMapping(value = "/testRedirect_3")public void testRedirect_3(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testRedirect_3 function");System.out.println("into testRedirect_3 function");String url = "http://www.baidu.com";try {response.sendRedirect(url);} catch (IOException e) {e.printStackTrace();}}
3.2.2利用HttpServletRespons对象同web服务重定向
代码：
/*** retrun same web project redirect* @param request HttpServletRequest* @param response HttpServletResponse* @return redirect same web project*/@RequestMapping(value = "/testRedirect_4")public void testRedirect_4(HttpServletRequest request, HttpServletResponse response) {logger.debug("into TestController中的testRedirect_4 function");System.out.println("into TestController中的testRedirect_4 function");String url = "/testRedirect_3";try {response.sendRedirect(url);} catch (IOException e) {e.printStackTrace();}}
4.1跨web项目不能转发
代码：
/*** retrun cross web project forward* @param request HttpServletRequest* @param response HttpServletResponse* @return forward cross web project* @note fail. Only the same web project forwarding*/@RequestMapping(value = "/testForward_1")public void testForward_1(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testForward_1 function");System.out.println("into testForward_1 function");String url = "http://www.baidu.com";try {request.getRequestDispatcher(url).forward(request, response);} catch (ServletException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}System.out.println("After the forwarding is completed,the code can also run.");}
4.2同web项目转发
代码：
/*** retrun same web project forward* @param request HttpServletRequest* @param response HttpServletResponse* @return forward same web project*/@RequestMapping(value = "/testForward_2")public void testForward_2(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testForward_2 function");System.out.println("into testForward_2 function");String url = "/testReturnPage";try {request.getRequestDispatcher(url).forward(request, response);} catch (ServletException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}System.out.println("After the forwarding is completed,the code can also run.");}
5.1流输出，用于下载文件
代码：
/*** retrun stream for downlaod file* @param request HttpServletRequest* @param response HttpServletResponse*/@RequestMapping(value = "/testReturnStream")public void testReturnStream(HttpServletRequest request, HttpServletResponse response) {logger.debug("into testReturnStream function");System.out.println("into testReturnStream function");byte[] bts = new byte[8192];int len = -1;try {
// set type is dawnloadresponse.setHeader("content-Type", "application/force-download");
// set file name and charsetresponse.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode("test.log", "utf-8"));OutputStream output = response.getOutputStream();File file = new File("./logs/log.log");FileInputStream input = new FileInputStream(file);while ((len = input.read(bts)) != -1) {output.write(bts, 0, len);}} catch (IOException e) {e.printStackTrace();}}
方法后代码：
}
对于一般的web项目来说， 以上五种返回形式应该是比较全面了。几乎也都说明了每种返回形式的应用场景。如有疏漏或错误，请不吝指出。