spring boot 搭建web项目常见五种返回形式

在web项目中一般常见的五种返回形式：

　　代码见：https://github.com/BenMario315/SpringBootLearn，demo

1. 返回页面，使用模板引擎，spring boot推荐使用thymeleaf，类似的还有freemarker等。
2. 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。
3. 返回重定向，一些较少的业务需求。
4. 转发，一些较少的业务需求。
5. 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 dawnload
            response.setHeader("content-Type", "application/force-download");
//            set file name and charset
            response.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。