Handling Character Encoding and JSON Mapping in a Java Backend with Servlet Filters and MyBatis

Character Encoding

Due to time pressure the author relied on log analysis and basic Java knowledge to solve a character‑encoding issue, ensuring that both the build configuration and the servlet filter use UTF‑8.

In build.gradle the encoding is set as follows:

tasks.withType(JavaCompile) {

    options.encoding = "UTF-8"

}

The servlet filter reads the request and response streams, logs them, and then writes the response back using the same UTF‑8 charset to avoid garbled output:

@Override
public void doFilter(ServletRequest request, ServletResponse response,
                     FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse resp = (HttpServletResponse) response;
    ResponseWrapper responseWrapper = new ResponseWrapper(resp);
    RequestWrapper requestWrapper = new RequestWrapper(req);
    String url = requestWrapper.getRequestURI();
    String queryArgs = requestWrapper.getQueryString();
    queryArgs = queryArgs == null ? requestWrapper.getBody() : queryArgs;
    long start = Time.getTimeStamp();
    chain.doFilter(requestWrapper == null ? request : requestWrapper, responseWrapper);
    long end = Time.getTimeStamp();
    byte[] bytes = responseWrapper.getContent();
    String respContent = new String(bytes, Constant.UTF_8);
    logger.info("请求:{},耗时:{}ms,参数:{},响应:{}", url, end - start, queryArgs, respContent);
    response.getOutputStream().write(respContent.getBytes(Constant.UTF_8));
}

Database Fields Combined into JSON

The backend needs to return four status‑count fields from the database as a JSON array. Instead of post‑processing, a custom MyBatis typeHandler is used to convert the semicolon‑separated string into a JSON array.

typehandler

package com.okay.family.common.typehandler;

import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import com.okay.family.fun.frame.SourceCode;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedJdbcTypes;
import org.apache.ibatis.type.MappedTypes;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Arrays;
import java.util.List;

/**
 * Convert the map result stored in the database into JSON format
 */
@MappedTypes(JSONObject.class)
@MappedJdbcTypes(JdbcType.VARCHAR)
public class ResultArrayHandler extends BaseTypeHandler<JSONArray> {

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, JSONArray parameter, JdbcType jdbcType) throws SQLException {
        ps.setString(i, String.valueOf(parameter.toJSONString()));
    }

    @Override
    public JSONArray getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String sqlJson = rs.getString(columnName);
        if (null != sqlJson) {
            JSONArray result = new JSONArray();
            List<String> asList = Arrays.asList(sqlJson.split(";"));
            asList.forEach(x -> {
                String[] split = x.split("=", 2);
                result.add(SourceCode.getJson("text=" + split[0], "amount=" + split[1]));
            });
        }
        return null;
    }

    @Override
    public JSONArray getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String sqlJson = rs.getString(columnIndex);
        if (null != sqlJson) {
            JSONArray result = new JSONArray();
            List<String> asList = Arrays.asList(sqlJson.split(";"));
            asList.forEach(x -> {
                String[] split = x.split("=", 2);
                result.add(SourceCode.getJson("text=" + split[0], "amount=" + split[1]));
            });
        }
        return null;
    }

    @Override
    public JSONArray getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String sqlJson = cs.getString(columnIndex);
        if (null != sqlJson) {
            JSONArray result = new JSONArray();
            List<String> asList = Arrays.asList(sqlJson.split(";"));
            asList.forEach(x -> {
                String[] split = x.split("=", 2);
                result.add(SourceCode.getJson("text=" + split[0], "amount=" + split[1]));
            });
        }
        return null;
    }
}

Mapper Configuration

The MyBatis resultMap references the custom type handler to map the concatenated status string to the JSON list field.

<resultMap type="com.okay.family.common.bean.casecollect.response.CollectionRunResultDetailBean" id="CollectionRunResultDetailBean">
    <result property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="envName" column="envName"/>
    <result property="runId" column="runId"/>
    <result property="caseNum" column="caseNum"/>
    <result property="result" column="result"/>
    <result property="startTime" column="start"/>
    <result property="endTime" column="end"/>
    <result property="list" column="list" typeHandler="com.okay.family.common.typehandler.ResultArrayHandler"/>
</resultMap>

The corresponding SQL statement concatenates the four status counts into a single string that the type handler later splits:

<select id="getCollectionRunDetail" parameterType="java.lang.Integer" resultMap="CollectionRunResultDetailBean">
    select r.collectionId id, t.name, s.name envName, r.runId, r.caseNum, c.name result, start, end,
    concat("成功=", r.success, ";失败=", r.fail, ";无法运行=", r.unrun, ";用户错误=", r.userError) list
    from ...
    where runId = #{0}
</select>

The article concludes with a reference to the original WeChat public account "FunTester" where more original technical articles are published.