com.yang.entity.SUser Query: select * from s_user XXXX Parameters: XXXX

短命女 2022-11-04 00:58 176阅读 0赞

## java.sql.SQLException: Cannot create com.yang.entity.SUser: com.yang.entity.SUser Query: select \* from s\_user where username=? and password=? Parameters: \[yang, 123456\] ##

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**报错内容：**

java.sql.SQLException: Cannot create com.yang.entity.SUser: com.yang.entity.SUser Query: select * from s_user where username=? and password=? Parameters: [yang, 123456]
    	at org.apache.commons.dbutils.AbstractQueryRunner.rethrow(AbstractQueryRunner.java:392)
    	at org.apache.commons.dbutils.QueryRunner.query(QueryRunner.java:351)
    	at org.apache.commons.dbutils.QueryRunner.query(QueryRunner.java:289)
    	at com.yang.util.JdbcUtil.queryOne(JdbcUtil.java:48)
    	at com.yang.dao.impl.UserDaoImpl.checkAdmin(UserDaoImpl.java:17)
    	at com.yang.service.impl.UserServiceImpl.checkAdmin(UserServiceImpl.java:19)
    	at com.yang.controller.UserServlet.adminLogin(UserServlet.java:99)
    	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    	at java.lang.reflect.Method.invoke(Method.java:498)
    	at com.yang.controller.BaseServlet.service(BaseServlet.java:19)
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    	at com.yang.filter.UserFilter.doFilter(UserFilter.java:28)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
    	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
    	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
    	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
    	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
    	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
    	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1634)
    	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    	at java.lang.Thread.run(Thread.java:748)

--------------------

今天利用commons-dbUtils工具包连接数据库，在访问数据库获得数据的时候出现了报错。

## 解决：实体类中创建无参构造 ##

--------------------

### 思考和解决的过程： ###

我自己通过common-dbutil工具包再次封装的方法：

/*查询多条数据*/
    public static <T> List<T> queryList(Class clazz, String sql, Object... args){ 
        try { 
            BasicRowProcessor brp = new BasicRowProcessor(new GenerousBeanProcessor());
            return runner.query(sql,new BeanListHandler<T>(clazz,brp),args);
        } catch (SQLException e) { 
            e.printStackTrace();
        }
        return null;
    }

**实体类**：

public class SUser implements Serializable { 
    
      private String id;
      private String username;
      private String password;
      private Integer type;
    
      public SUser(String id, String username, String password, Integer type) { 
        this.id = id;
        this.username = username;
        this.password = password;
        this.type = type;
      }
    
      @Override
      public String toString() { 
        return "SUser{" +
                "id='" + id + '\'' +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", type=" + type +
                '}';
      }
    
      public String getId() { 
        return id;
      }
    
      public void setId(String id) { 
        this.id = id;
      }
    
      public String getUsername() { 
        return username;
      }
    
      public void setUsername(String username) { 
        this.username = username;
      }
    
    
      public String getPassword() { 
        return password;
      }
    
      public void setPassword(String password) { 
        this.password = password;
      }
    
    
      public Integer getType() { 
        return type;
      }
    
      public void setType(Integer type) { 
        this.type = type;
      }
    }

dao层的方法：

@Override
    public SUser checkAdmin(String username, String password) { 
       return JdbcUtil.queryOne(SUser.class, "select * from s_user where username=? and password=?", username, password);
    }

> 思考：报错信息是没有不能创建SUser这个类。但是我又SUser实体类呀，而且dao层方法的参数也没有问题。那为什么不能创建SUser类呢？
> 
> 后来突然想到封装jdbc工具类的时候方法里面用到的反射Class,如果是反射的那问题应该是出现在反射的时候没有成功创建SUser对象。后来想利用**反射**创建来的时候会用到**无参构造**。**终于找到原因了**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hpYW96aHV6aHV5YW5n_size_16_color_FFFFFF_t_70]  
总结：所以在创建实体类的时候，防止后面出现错误。我们在创建的时候就将无参,全参构造器都创建好。

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