需求：前端JSON数据，后端用String[]接收，用varchar来存入数据库。
myabtis默认的typehandler不支持，需要自定义处理器来操作。

代码示例

	//前端json

  {
   "specifications": [
      "标准"
    ]
  }
  //java字段
  private String[] specifications;

异常信息做参考

Caused by: java.lang.IllegalStateException: Type handler was null on parameter mapping for property 'specifications'. It was either not specified and/or could not be found for the javaType ([Ljava.lang.String;) : jdbcType (VARCHAR) combination.
	at org.apache.ibatis.mapping.ParameterMapping$Builder.validate(ParameterMapping.java:119)
	at org.apache.ibatis.mapping.ParameterMapping$Builder.build(ParameterMapping.java:104)
	at org.apache.ibatis.builder.SqlSourceBuilder$ParameterMappingTokenHandler.buildParameterMapping(SqlSourceBuilder.java:143)
	at org.apache.ibatis.builder.SqlSourceBuilder$ParameterMappingTokenHandler.handleToken(SqlSourceBuilder.java:87)
	at org.apache.ibatis.parsing.GenericTokenParser.parse(GenericTokenParser.java:77)
	at org.apache.ibatis.builder.SqlSourceBuilder.parse(SqlSourceBuilder.java:50)
	at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:42)
	at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:305)
	at org.apache.ibatis.executor.statement.BaseStatementHandler.<init>(BaseStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.<init>(PreparedStatementHandler.java:41)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.<init>(RoutingStatementHandler.java:46)
	at org.apache.ibatis.session.Configuration.newStatementHandler(Configuration.java:681)
	at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:48)
	at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49)
	at com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor.intercept(MybatisPlusInterceptor.java:106)
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:62)
	at com.sun.proxy.$Proxy167.update(Unknown Source)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:194)
	... 110 common frames omitted

实现步骤

1.自定义TypeHandler类

//注解作用是注册处理器，还有一种注册方式是通过xml文件配置
@MappedJdbcTypes(JdbcType.VARCHAR)
@MappedTypes({java.lang.String[].class})
public class JsonStringArrayTypeHandler extends BaseTypeHandler<String[]> {
    private static final ObjectMapper mapper = new ObjectMapper();

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, String[] parameter, JdbcType jdbcType) throws SQLException {
        ps.setString(i, toJson(parameter));
    }

    @Override
    public String[] getNullableResult(ResultSet rs, String columnName) throws SQLException {
        return this.toObject(rs.getString(columnName));
    }

    @Override
    public String[] getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        return this.toObject(rs.getString(columnIndex));
    }

    @Override
    public String[] getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        return this.toObject(cs.getString(columnIndex));
    }

    private String toJson(String[] params) {
        try {
            return mapper.writeValueAsString(params);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "[]";
    }

    private String[] toObject(String content) {
        if (content != null && !content.isEmpty()) {
            try {
                return (String[]) mapper.readValue(content, String[].class);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        } else {
            return null;
        }
    }
}

2.在Java实体类对应的mapper.xml 修改

 <result property="specifications" column="specifications" jdbcType="VARCHAR" typeHandler="包名.JsonStringArrayTypeHandler"/>
       

3.在Java实体类字段添加注解

@TableField(jdbcType = JdbcType.VARCHAR,typeHandler = JsonStringArrayTypeHandler.class)
private String[] specifications;

4.大功告成

ps：自定义TtypeypeHandler有两种方式，本文只列出了作者在项目中使用过的方式。

标签：java,String,自定义,TypeHandler,return,ibatis,apache,org
来源： https://www.cnblogs.com/dixueli/p/16396500.html