When mybatis was used to process a field of type char, there was an error:

org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.result.ResultMapException: Error attempting to get column '字段名' from result set.  Cause: java.lang.StringIndexOutOfBoundsException: String index out of range: 0
	at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:79)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:447)
	at com.sun.proxy.$Proxy24.selectList(Unknown Source)
	at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:231)
	at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:122)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:64)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
	at com.sun.proxy.$Proxy67.selectOldPhoneInfo(Unknown Source)
	at com.hibroad.compatibleweb.service.impl.FallDownServiceImpl.phonePup(FallDownServiceImpl.java:210)
	at com.hibroad.compatibleweb.service.impl.FallDownServiceImpl$$FastClassByCGLIB$$a692b24b.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:713)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
	at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:646)
	at com.hibroad.compatibleweb.service.impl.FallDownServiceImpl$$EnhancerByCGLIB$$28859386.phonePup(<generated>)
	at com.hibroad.compatibleweb.handler.FallDownHandler.doHandler(FallDownHandler.java:82)
	at com.hibroad.compatibleweb.handler.FamilyApiHandler_Web.mappingClass(FamilyApiHandler_Web.java:238)
	at com.hibroad.compatibleweb.handler.FamilyApiHandler_Web.service(FamilyApiHandler_Web.java:165)
	at com.hibroad.compatibleweb.handler.FamilyApiHandler_Web.service_get(FamilyApiHandler_Web.java:57)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:214)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:748)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:931)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:822)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at com.hibroad.util.CorsFilter.doFilter(CorsFilter.java:24)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:1025)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.ibatis.executor.result.ResultMapException: Error attempting to get column '字段名' from result set.  Cause: java.lang.StringIndexOutOfBoundsException: String index out of range: 0
	at org.apache.ibatis.type.BaseTypeHandler.getResult(BaseTypeHandler.java:68)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyAutomaticMappings(DefaultResultSetHandler.java:471)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:364)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForSimpleResultMap(DefaultResultSetHandler.java:318)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:293)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:266)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:180)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:63)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:78)
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:303)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:154)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:102)
	at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:141)
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61)
	at com.sun.proxy.$Proxy136.query(Unknown Source)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:120)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:113)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:434)
	... 67 more
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: 0
	at java.lang.String.charAt(String.java:658)
	at org.apache.ibatis.type.CharacterTypeHandler.getNullableResult(CharacterTypeHandler.java:37)
	at org.apache.ibatis.type.CharacterTypeHandler.getNullableResult(CharacterTypeHandler.java:26)
	at org.apache.ibatis.type.BaseTypeHandler.getResult(BaseTypeHandler.java:66)

This field is of char type, and everything else is good. For this error report, the problem lies in mybatis processing char. Let’s see how mybatis processes char, and attach the source code of mybatis processing

/**
 *    Copyright 2009-2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.type;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * @author Clinton Begin
 */
public class CharacterTypeHandler extends BaseTypeHandler<Character> {

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, Character parameter, JdbcType jdbcType) throws SQLException {
    ps.setString(i, parameter.toString());
  }

  @Override
  public Character getNullableResult(ResultSet rs, String columnName) throws SQLException {
    String columnValue = rs.getString(columnName);
    if (columnValue != null) {
      return columnValue.charAt(0);
    } else {
      return null;
    }
  }

  @Override
  public Character getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    String columnValue = rs.getString(columnIndex);
    if (columnValue != null) {
      return columnValue.charAt(0);
    } else {
      return null;
    }
  }

  @Override
  public Character getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    String columnValue = cs.getString(columnIndex);
    if (columnValue != null) {
      return columnValue.charAt(0);
    } else {
      return null;
    }
  }
}

If you only judge whether it is null, you will directly charat (0). If the columnvalue is empty, you will directly get an exception. How to rewrite a typehandle <Character>

package com.lpc.config;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class MyCharacterTypeHandler extends BaseTypeHandler<Character> {
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, Character parameter, JdbcType jdbcType)
            throws SQLException {
        ps.setString(i, parameter.toString());
    }

    @Override
    public Character getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String columnValue = rs.getString(columnName);
        if (columnValue != null && !columnValue.isEmpty() ) {
            return columnValue.charAt(0);
        } else {
            return null;
        }
    }

    @Override
    public Character getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String columnValue = rs.getString(columnIndex);
        if (columnValue != null && !columnValue.isEmpty() ) {
            return columnValue.charAt(0);
        } else {
            return null;
        }
    }

    @Override
    public Character getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String columnValue = cs.getString(columnIndex);
        if (columnValue != null && !columnValue.isEmpty() ) {
            return columnValue.charAt(0);
        } else {
            return null;
        }
    }
}

Then write in mybatis-config.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeHandlers>
        <typeHandler javaType="java.lang.Character" jdbcType="CHAR" handler="com.lpc.config.MyCharacterTypeHandler" />
    </typeHandlers>
</configuration>

Add mybatis config configuration in application.properties

mybatis.config-location=classpath:mybatis-config.xml

This field in the mapper.xml file needs to be modified as follows:

<result column="orderNum" property="orderNum" jdbcType="CHAR" typeHandler="com.lpc.config.MyCharacterTypeHandler"/>

All right, restart it

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