为什么注入的bean值为null

Question

我有自定义标签。当我注入spring消息资源并想要访问属性文件时，注入的bean始终为null。 我做错了什么，

 @Component
public class GridColumnsCutomTagHander extends TagSupport {

/**
 * 
 */
private static final long serialVersionUID = 1L;

@Inject
private MessageSource messageSource;

private String propertyFileName;

/**
 * @return the propertyFileName
 */
public String getPropertyFileName() {
    return this.propertyFileName;
}

/**
 * @param propertyFileName
 *            the propertyFileName to set
 */
public void setPropertyFileName(String propertyFileName) {
    this.propertyFileName = propertyFileName;
}

@Override
public int doStartTag() throws JspException {

    try {
        JspWriter out = pageContext.getOut();
        String gridColumnValues = messageSource.getMessage(propertyFileName,
                null, EWMSUser.getCurrentLanguageLocale());
        out.println(gridColumnValues );
    } catch (IOException e) {
        e.printStackTrace();
    }

    return (SKIP_BODY);
}

请帮我弄清问题在哪里

Answer 1

根据我的经验，如果当前类具有servletContext环境 ，则可以将MessageSource注入成功 。因此，您需要将其注入 contronller < / strong> layer，然后将其作为构造参数传递给当前标记类。

为了做到这一点，我认为你不应该使用@Componment来初始化GridColumnsCutomTagHander类，你需要手动在你的代码中创建它.Below是我的解决方案：

• 类 GridColumnsCutomTagHander
的代码

public class GridColumnsCutomTagHander extends TagSupport {


private static final long serialVersionUID = 1L;


private MessageSource messageSource;

public GridColumnsCutomTagHander(){
}

public GridColumnsCutomTagHander(MessageSource messageSource){
   this.messageSource=messageSource;
}

private String propertyFileName;

/**
 * @return the propertyFileName
 */
public String getPropertyFileName() {
    return this.propertyFileName;
}

/**
 * @param propertyFileName
 *            the propertyFileName to set
 */
public void setPropertyFileName(String propertyFileName) {
    this.propertyFileName = propertyFileName;
}

@Override
public int doStartTag() throws JspException {

    try {
        JspWriter out = pageContext.getOut();
        String gridColumnValues = messageSource.getMessage(propertyFileName,
                null, EWMSUser.getCurrentLanguageLocale());
        out.println(gridColumnValues );
    } catch (IOException e) {
        e.printStackTrace();
    }

    return (SKIP_BODY);
}

• 在控制器图层类中使用它：

@Controller   
public TestController{

 @Inject
 private MessageSource messageSource;

@RequestMapping("test")
 public void test(){
   new GridColumnsCutomTagHander(messageSource);//now the messageSource is not null
 }
}