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Java中equals()方法判断字符串相等时报NullPointerException,如s.equals("String")

作者:互联网

1、题目

阅读getCondition方法,找出其中的错误点并修复

2、代码片段

import java.sql.Timestamp;
import java.util.Arrays;
import java.util.Date;
import java.util.List;
import java.util.Map;
​
public class SQLConstructor {
    
    public static void main(String[] args) {
        System.out.println("阅读getCondition方法,找出其中的错误点并修复");
        System.out.println("要求不能使用第三方包,只能用JDK中的方法");
        System.out.println("要求对修复之后的方法进行测试,并打印结果");
    }
​
    /**
     * 构造查询SQL语句
     * @param searchParams
     * @param values
     * @return 返回SQL
     */
    private static String getCondition(Map<String, Object> searchParams, List<Object> values) {
​
        StringBuilder sb = new StringBuilder();
​
        for (String s : searchParams.keySet()) {
            if ("startTime".equals(s)) {
                if (String.valueOf(searchParams.get("startTime")).contains(":")) {
                    throw new RuntimeException("请使用时间进行查询!");
                } else {
                    sb.append("UPDATE_TIME >= ? AND ");
                    values.add(paseDateFromLongStr(searchParams.get(s).toString()));
                }
            } else if (s.equals("DIC_TYPE")) {
                sb.append(" DIC_TYPE IN (?,?,?) AND ");
                String[] split = String.valueOf(searchParams.get(s)).split(",");
                if (split.length == 3) {
                    values.addAll(Arrays.asList(split));
                } else if (split.length < 3) {
                    // TODO 处理非3的情况
                }
            } else if ("ITEM_ID".equals(s)) {
                sb.append("ITEM_ID =? AND ");
​
            } else if ("ORG_ID".equals(s) || "COMPANY_ID".equals(s)) {
                sb.append(s + " =? AND ");
                values.add(searchParams.get(s));
            }
​
        }
        if (!searchParams.keySet().contains("DIC_CODE")) {
            sb.append(" DIC_CODE IN ('JOB_DUTY','GROUP_JOB_DUTY','USER_POST') AND ");
        }
        return sb.toString();
​
    }
​
    public static Date paseDateFromLongStr(String dateStr) {
        Date date = null;
        try {
            Long timestamp = Long.parseLong(dateStr);
            date = new Timestamp(timestamp);
        } catch (Exception e) {
            throw new RuntimeException(
                    "请检查日期格式(需使用时间戳格式的时间)");
        }
        return date;
    }
}

3、代码解答

import java.sql.Timestamp;
import java.util.ArrayList; 
import java.util.Arrays;
import java.util.Date;
import java.util.HashMap; 
import java.util.List;
import java.util.Map;

public class SQLConstructor {
    
    public static void main(String[] args) {
        System.out.println("阅读getCondition方法,找出其中的错误点并修复");
        System.out.println("要求不能使用第三方包,只能用JDK中的方法");
        System.out.println("要求对修复之后的方法进行测试,并打印结果");
        

        Map<String, Object> map1 = new HashMap<String, Object>();
        map1.put("startTime", "1648349346");  
        List<Object> list1=new ArrayList<Object>();
        String str1 =SQLConstructor.getCondition(map1, list1);
        System.out.println(str1);   //UPDATE_TIME >= ? AND  DIC_CODE IN ('JOB_DUTY','GROUP_JOB_DUTY','USER_POST') AND

        Map<String, Object> map2 = new HashMap<String, Object>();
        map1.put("startTime", "2022-03-27 10:49:06");  
        List<Object> list2=new ArrayList<Object>();
        String str2 =SQLConstructor.getCondition(map2, list2);
        System.out.println(str2);   // DIC_CODE IN ('JOB_DUTY','GROUP_JOB_DUTY','USER_POST') AND

        System.out.println("========================================");

        Map<String, Object> map3 = new HashMap<String, Object>();
        //方便测试全放到map3中
        map3.put("DIC_TYPE", "value2");
        map3.put("ITEM_ID", "value3");
        map3.put("ORG_ID", "value4");
        map3.put("COMPANY_ID", "value5");  
        List<Object> list3=new ArrayList<Object>();
        String str3 =SQLConstructor.getCondition(map3, list3);
        System.out.println(str3);   //  ORG_ID =? AND  DIC_TYPE IN (?,?,?) AND ITEM_ID =? AND COMPANY_ID =? AND  DIC_CODE IN ('JOB_DUTY','GROUP_JOB_DUTY','USER_POST') AND

        //map.put(null, "value");  //s.equals("DIC_TYPE" 报错  NullPointerException
    }

    /**
     * 构造查询SQL语句
     * @param searchParams
     * @param values
     * @return 返回SQL
     */
    private static String getCondition(Map<String, Object> searchParams, List<Object> values) {

        StringBuilder sb = new StringBuilder();

        for (String s : searchParams.keySet()) {
            if ("startTime".equals(s)) {
                if (String.valueOf(searchParams.get("startTime")).contains(":")) {
                    throw new RuntimeException("请使用时间进行查询!");
                } else {
                    sb.append("UPDATE_TIME >= ? AND ");
                    values.add(paseDateFromLongStr(searchParams.get(s).toString()));
                }
            // } else if (s.equals("DIC_TYPE")) {   修改前
            } else if ("DIC_TYPE".equals(s)) {
                sb.append(" DIC_TYPE IN (?,?,?) AND ");
                String[] split = String.valueOf(searchParams.get(s)).split(",");
                if (split.length == 3) {
                    values.addAll(Arrays.asList(split));
                } else if (split.length < 3) {
                    // TODO 处理非3的情况
                }
            } else if ("ITEM_ID".equals(s)) {
                sb.append("ITEM_ID =? AND ");

            } else if ("ORG_ID".equals(s) || "COMPANY_ID".equals(s)) {
                sb.append(s + " =? AND ");
                values.add(searchParams.get(s));
            }

        }
        if (!searchParams.keySet().contains("DIC_CODE")) {
            sb.append(" DIC_CODE IN ('JOB_DUTY','GROUP_JOB_DUTY','USER_POST') AND ");
        }
        return sb.toString();

    }

    public static Date paseDateFromLongStr(String dateStr) {
        //1648349346   2022-03-27 10:49:06
        Date date = null;
        try {
            Long timestamp = Long.parseLong(dateStr);
            date = new Timestamp(timestamp);
        } catch (Exception e) {
            throw new RuntimeException(
                    "请检查日期格式(需使用时间戳格式的时间)");
        }
        return date;
    }
}

由于个人能力有限,如有不足之处,欢迎指正。

标签:searchParams,Java,String,equals,DIC,new,ID,NullPointerException
来源: https://www.cnblogs.com/CodedogWorld/p/16067105.html