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

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 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。

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spring boot 搭建web项目常见五种返回形式

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