Analysis of the reason why JavaWeb dbutils cannot find the content when executing SQL commands and traversing the result set

The reason why JavaWeb dbutils cannot find the content when executing SQL command and traversing the result set and the handling method are as follows:

When traversing the result set, only the bean object will be traversed and only the first line will be output (the first line is the object instantiated by the userentity class). Therefore, re. Getrepotablename() is required here to call the corresponding content through the object

In this way, you can get the value

PS: the details of dbutils of JavaWeb are as follows:

1、 What are dbutils and their functions

Dbutils was written by Apache. Dbutils is a database operation utility in Java programming. It is small, simple and practical.

Dbutils encapsulates the operation of JDBC and simplifies the operation of JDBC. You can write less code.

　　1. For the data table reading operation, it can convert the results into Java sets such as list, array and set, which is convenient for programmers to operate;

　　2. For the write operation of the data table, it also becomes very simple (just write SQL statements)

　　3. You can use data source, JNDI, database connection pool and other technologies to optimize performance -- reuse the built database connection objects

2、 Three core objects of dbutils

2.1 queryrunner class

The query runner provides APIs for SQL statement operations It mainly has three methods: query () is used to execute select, update () is used to execute insert, update, delete, and batch (). Later, the following will introduce the usage of these methods in detail.

2.2. Resultsethandler interface

It is used to define how to encapsulate the result set after the select operation It has a total of 9 commonly used implementation classes. I will introduce how to use them in detail below.

2.3. Dbutils

It is a tool class that defines methods to close resources and transactions

3、 How to use the dbutils framework

3.1 use steps

Import the corresponding jar package

Create queryrunner object

Execute the select statement using the query method

Encapsulating result sets with resultsethandler

Use the dbutils class to free up resources

3.2 examples

Note: I use c3p0 connection pool

4、 Detailed explanation of three core objects of dbutils

4.1. Queryrunner object

　　　　4.1. 1. Constructor

　　　　　　　　 new QueryRunner(); Its transactions can be controlled manually. 　　　　　　　　　　　　　　　　　　　　

That is, the method (such as query, update, batch) called by this object must have a connection object in its parameters.

　　　　　　 new QueryRunner(DataSource ds); Its transactions are automatically controlled. One SQL and one transaction. 　　　　　　　　　　　　　　　　　　　　　　

The connection object is not required in the parameters of the methods called by this object (such as query, update and batch).

　　　　4.1. 2. Common methods

4.2. Resultsethandler interface

　　　　4.2. 1. It has nine result processors

Arrayhandler: suitable for taking 1 record. Encapsulate the value of each column of the record into an array object [] arraylisthandler: suitable for taking multiple records. Encapsulate the value of each column of each record into an array object [], and encapsulate the array into a list. Columnlisthandler: get the data of a column. Encapsulated in a list. Keyedhandler: take multiple records, encapsulate each record into a map, and then encapsulate the map into another map. Key is the specified field value. Maphandler: suitable for taking 1 record. Put the column name and column value of the current record into a map maplisthandler: suitable for multiple records. Encapsulate each record into a map, and then encapsulate the map into a list. Scalarhandler: beanhandler beanlisthandler is suitable for single row and single column data

　　　　4.2. 2. Instance

5、 Use dbutils to do an example of addition, deletion, modification and query

summary

The above is the reason why JavaWeb dbutils cannot find the content when executing SQL commands and traversing the result set. I hope it will be helpful to you. If you have any questions, please leave me a message and Xiaobian will reply to you in time. Thank you very much for your support of programming tips!