Cannot call sendError() after the response has been committed - baiyangliu - 博客頻道 - CSDN.NET

當response提交后，不能調用sendError()，什么意思？

出現這個錯誤，一定是多次response導致的。可以這么理解，承載客戶端和服務器進行Http交互的Socket連接已經關閉了，而你還試圖發送數據給客戶端，顯然會出錯。就好比我倆打電話，我都掛電話了，你還在“喂喂喂”。

例如下面這段代碼就會出現此錯誤：

import java.io.Writer;

import javax.servlet.http.HttpServletResponse;

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionSupport;

public class LoginAction extends ActionSupport {

    /**
     *
     */
    private static final long serialVersionUID = 1L;
    private String userName;
    private String pwd;
    private String verifyCode;
    private String ajax;

    // 錯誤的寫法
    @Override
    public String execute() throws Exception {
        // 通過ajax登錄
        if (ajax != null) {
            HttpServletResponse response = ServletActionContext.getResponse();
            Writer writer = response.getWriter();
            writer.write("登錄成功!");
            writer.flush();
            writer.close();
        }
        return SUCCESS;
    }

    // 正確寫法
    public String login1() throws Exception {
        if (ajax != null) {
            HttpServletResponse response = ServletActionContext.getResponse();
            Writer writer = response.getWriter();
            writer.write("登錄成功!");
            writer.flush();
            writer.close();
            return null;
        }
        return SUCCESS;
    }

    // 正確寫法
    public String login2() throws Exception {
        if (ajax != null) {
            HttpServletResponse response = ServletActionContext.getResponse();
            Writer writer = response.getWriter();
            writer.write("登錄成功!");
            writer.flush();
            writer.close();
        }
        return null;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public String getVerifyCode() {
        return verifyCode;
    }

    public void setVerifyCode(String verifyCode) {
        this.verifyCode = verifyCode;
    }

    public String getAjax() {
        return ajax;
    }

    public void setAjax(String ajax) {
        this.ajax = ajax;
    }
}

import java.io.Writer;import javax.servlet.http.HttpServletResponse;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionSupport;public class LoginAction extends ActionSupport {	/**	 * 	 */	private static final long serialVersionUID = 1L;	private String userName;	private String pwd;	private String verifyCode;	private String ajax;	// 錯誤的寫法	@Override	public String execute() throws Exception {		// 通過ajax登錄		if (ajax != null) {			HttpServletResponse response = ServletActionContext.getResponse();			Writer writer = response.getWriter();			writer.write("登錄成功!");			writer.flush();			writer.close();		}		return SUCCESS;	}	// 正確寫法	public String login1() throws Exception {		if (ajax != null) {			HttpServletResponse response = ServletActionContext.getResponse();			Writer writer = response.getWriter();			writer.write("登錄成功!");			writer.flush();			writer.close();			return null;		}		return SUCCESS;	}	// 正確寫法	public String login2() throws Exception {		if (ajax != null) {			HttpServletResponse response = ServletActionContext.getResponse();			Writer writer = response.getWriter();			writer.write("登錄成功!");			writer.flush();			writer.close();		}		return null;	}	public String getUserName() {		return userName;	}	public void setUserName(String userName) {		this.userName = userName;	}	public String getPwd() {		return pwd;	}	public void setPwd(String pwd) {		this.pwd = pwd;	}	public String getVerifyCode() {		return verifyCode;	}	public void setVerifyCode(String verifyCode) {		this.verifyCode = verifyCode;	}	public String getAjax() {		return ajax;	}	public void setAjax(String ajax) {		this.ajax = ajax;	}}

以上為登錄測試代碼（Struts2），在以上示例中，如果判斷為ajax!=null成立，那么一定會報如題所示的錯誤，原因就是：if子句里已經做了一次response，在writer.close();的時候，本次response已經完成；但是緊接着在return SUCCESS;的時候，相當於又做了一次response，所以就出錯了~

類似的錯誤也會出現於以下代碼中：

protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            Writer writer = response.getWriter();
            writer.write("Hello");
            writer.flush();
            writer.close();

            response.sendRedirect("http://blog.csdn.net/baiyanglu/article/details/8076104");
        }

protected void doGet(HttpServletRequest request, HttpServletResponse response) 				throws ServletException, IOException {			Writer writer = response.getWriter();			writer.write("Hello");			writer.flush();			writer.close();			response.sendRedirect("http://blog.csdn.net/baiyanglu/article/details/8076104");		}

出現本錯誤后，web前端能夠接收到第一次response的內容（就是說，掛電話之前說的話，我還是可以聽到的，掛電話后講的，當然聽不到咯~），不會報錯，只會在后台顯示出錯了

來自為知筆記(Wiz)