用 Spring 取得 JSP 執行後的字串內容

為了取得執行後的字串內容，我們需要建立 Response 並且替換 PrintWriter，這樣才有辦法取得執行後的內容。

接著可以從 Spring 的 ViewResolver 去取得 View，再透過 View 去處理 render 前的包裝，最後才由 dispatcher 真正去處理 render 的動作。

想到要建立 Request 跟 Response 就感覺讓人頭痛，還好 Spring 有提供 Mock 的類別可以簡單地去建立 Request 跟 Response。

JspRenderer

原始碼

1. package com.orion.webmvc.util; 
2.  
3. import java.io.IOException; 
4. import java.io.PrintWriter; 
5. import java.io.StringWriter; 
6. import java.io.UnsupportedEncodingException; 
7. import java.util.Locale; 
8. import java.util.Map; 
9.  
10. import javax.servlet.RequestDispatcher; 
11. import javax.servlet.ServletContext; 
12.  
13. import org.springframework.beans.factory.annotation.Autowired; 
14. import org.springframework.mock.web.MockHttpServletRequest; 
15. import org.springframework.mock.web.MockHttpServletResponse; 
16. import org.springframework.ui.Model; 
17. import org.springframework.web.servlet.View; 
18. import org.springframework.web.servlet.ViewResolver; 
19.  
20.  
21. public class JspRenderer { 
22.  
23.    @Autowired 
24.    private ServletContext servletContext; 
25.  
26.  
27.    private ViewResolver viewResolver; 
28.  
29.    public void setViewResolver(ViewResolver viewResolver) { 
30.        this.viewResolver = viewResolver; 
31.    } 
32.  
33.  
34.    public String render(String viewName, Model model)  
35.        throws IOException  
36.    { 
37.        return render(viewName, model.asMap()); 
38.    } 
39.  
40.    public String render(String viewName, Map<String,Object> modelMap)  
41.        throws IOException  
42.    { 
43.  
44.        RendererRequest request = new RendererRequest(servletContext); 
45.        RendererResponse response = new RendererResponse(); 
46.  
47.        try { 
48.            /* 透過 ViewResolver 取得 View 進行 render 的動作 */ 
49.            View view = viewResolver.resolveViewName( 
50.                viewName, Locale.getDefault() 
51.            ); 
52.            view.render(modelMap, request, response); 
53.  
54.            return response.getContentAsString(); 
55.        } 
56.        catch(Exception e) { 
57.            throw new IOException(e); 
58.        } 
59.    } 
60. } 
61.  
62.  
63. class RendererRequest extends MockHttpServletRequest { 
64.  
65.    private ServletContext servletContext; 
66.  
67.    public RendererRequest(ServletContext servletContext) { 
68.        this.servletContext = servletContext; 
69.    } 
70.  
71.    @Override 
72.    public RequestDispatcher getRequestDispatcher(String path) { 
73.        /* 需要透過真實的 RequestDispatcher 進行 Render */ 
74.        return servletContext.getRequestDispatcher(path); 
75.    } 
76. } 
77.  
78.  
79. class RendererResponse extends MockHttpServletResponse { 
80.  
81.    private StringWriter writer = new StringWriter(); 
82.  
83.    @Override 
84.    public PrintWriter getWriter() throws UnsupportedEncodingException { 
85.        /* 用 StringWriter 作為輸出的容器 */ 
86.        return new PrintWriter(writer); 
87.    } 
88.  
89.    @Override 
90.    public boolean isCommitted() { 
91.        /* true 是為了讓 View 可以採用 include 方式 Render 到 Response */ 
92.        return true; 
93.    } 
94.  
95.    @Override 
96.    public String getContentAsString() throws UnsupportedEncodingException { 
97.        /* 取得 Render 後的內容 */ 
98.        return writer.getBuffer().toString(); 
99.    } 
100. } 

package com.orion.webmvc.util;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.util.Locale;
import java.util.Map;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.ui.Model;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;


public class JspRenderer {

    @Autowired
    private ServletContext servletContext;


    private ViewResolver viewResolver;

    public void setViewResolver(ViewResolver viewResolver) {
        this.viewResolver = viewResolver;
    }


    public String render(String viewName, Model model) 
        throws IOException 
    {
        return render(viewName, model.asMap());
    }

    public String render(String viewName, Map<String,Object> modelMap) 
        throws IOException 
    {

        RendererRequest request = new RendererRequest(servletContext);
        RendererResponse response = new RendererResponse();

        try {
            /* 透過 ViewResolver 取得 View 進行 render 的動作 */
            View view = viewResolver.resolveViewName(
                viewName, Locale.getDefault()
            );
            view.render(modelMap, request, response);

            return response.getContentAsString();
        }
        catch(Exception e) {
            throw new IOException(e);
        }
    }
}


class RendererRequest extends MockHttpServletRequest {

    private ServletContext servletContext;

    public RendererRequest(ServletContext servletContext) {
        this.servletContext = servletContext;
    }

    @Override
    public RequestDispatcher getRequestDispatcher(String path) {
        /* 需要透過真實的 RequestDispatcher 進行 Render */
        return servletContext.getRequestDispatcher(path);
    }
}


class RendererResponse extends MockHttpServletResponse {

    private StringWriter writer = new StringWriter();

    @Override
    public PrintWriter getWriter() throws UnsupportedEncodingException {
        /* 用 StringWriter 作為輸出的容器 */
        return new PrintWriter(writer);
    }

    @Override
    public boolean isCommitted() {
        /* true 是為了讓 View 可以採用 include 方式 Render 到 Response */
        return true;
    }

    @Override
    public String getContentAsString() throws UnsupportedEncodingException {
        /* 取得 Render 後的內容 */
        return writer.getBuffer().toString();
    }
}

配置 spring.xml

原始碼

1. <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> 
2.    <property name="prefix" value="/WEB-INF/views/" /> 
3.    <property name="suffix" value=".jsp" /> 
4. </bean> 
5.  
6. <bean id="jspRenderer" class="com.orion.webmvc.util.JspRenderer"> 
7.    <property name="viewResolver" ref="viewResolver"/> 
8. </bean> 

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/views/" />
    <property name="suffix" value=".jsp" />
</bean>

<bean id="jspRenderer" class="com.orion.webmvc.util.JspRenderer">
    <property name="viewResolver" ref="viewResolver"/>
</bean>

使用範例

原始碼

1. //@Autowired 
2. //private JspRenderer jspRenderer; 
3.  
4. Map<String,Object> jspMap = new HashMap<String,Object>(); 
5. jspMap.put("jspMessage", "中文訊息測試"); 
6. jspMap.put("costMessage", 4567.89); 
7.  
8. String jspOutput = jspRenderer.render("/mailer/test", jspMap); 
9. System.out.println(jspOutput); 

//@Autowired
//private JspRenderer jspRenderer;

Map<String,Object> jspMap = new HashMap<String,Object>();
jspMap.put("jspMessage", "中文訊息測試");
jspMap.put("costMessage", 4567.89);

String jspOutput = jspRenderer.render("/mailer/test", jspMap);
System.out.println(jspOutput);

參考自：Render and capture the output of a JSP as a String | Technological Oddity