處理gson解析時類型不匹配或者空值問題

android開發(fā)的數(shù)據(jù)幾乎都是通過請求拿到后臺的json數(shù)據(jù),然后將數(shù)據(jù)解析成對應(yīng)的Bean

通常我們會將請求結(jié)果封裝成一個BaseResponse,比如這樣

package com.mjt.factory.base;

import com.google.gson.annotations.SerializedName;

import java.io.Serializable;

/**
 * Author: zhangsiqi
 * Email: zsq901021@sina.com
 * Date: 2018/1/25
 * Time: 11:09
 * Desc:
 */
public class BaseResponse<T> implements Serializable {

    public BaseResponse(int ret, String message, Error error) {
        this.ret = ret;
        this.message = message;
        this.error = error;
    }

    public BaseResponse(int ret, String message, T data) {
        this.ret = ret;
        this.message = message;
        this.data = data;
    }

    @SerializedName("ret")
    private int ret;

    @SerializedName("msg")
    private String message;

    @SerializedName("data")
    private T data;

    @SerializedName("error")
    private Error error;

    public Error getError() {
        return error;
    }

    public int getRet() {
        return ret;
    }

    public String getMessage() {
        return message;
    }

    public T getData() {
        return data;
    }

    public static class Error {

        public Error(int code, String msg) {
            this.code = code;
            this.msg = msg;
        }

        @SerializedName("code")
        private int code;
        @SerializedName("msg")
        private String msg = "";

        public int getCode() {
            return code;
        }

        public String getMsg() {
            return msg;
        }
    }
}

可以看到BaseResponse里data是object類型

但是遇到開發(fā)不規(guī)范的后臺,如果object為空他會返回給你""或者"null"這樣一個空字符串,這時候我們用object類型類接收就會拋一個java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING 的異常

那么怎么動態(tài)的處理這種問題呢

gson有一個TypeAdapter是可以讓開發(fā)者自定義處理類型問題的

package com.mjt.common.utils.gson;

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

import java.io.IOException;

/**
 * Copyright:mjt_pad_android
 * Author: liyang <br>
 * Date:2019/3/4 2:35 PM<br>
 * Desc: <br>
 */
public class GsonTypeAdapterFactory implements TypeAdapterFactory {
    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        final TypeAdapter<T> adapter = gson.getDelegateAdapter(this, type);
        return new TypeAdapter<T>() {
            @Override
            public void write(JsonWriter out, T value) throws IOException {
                adapter.write(out, value);
            }

            @Override
            public T read(JsonReader in) throws IOException {

                try {
                    return adapter.read(in);
                } catch (Throwable e) {
                    consumeAll(in);
                    return null;
                }

            }

            private void consumeAll(JsonReader in) throws IOException {
                if (in.hasNext()) {
                    JsonToken peek = in.peek();
                    if (peek == JsonToken.STRING) {
                        in.nextString();
                    } else if (peek == JsonToken.BEGIN_ARRAY) {
                        in.beginArray();
                        consumeAll(in);
                        in.endArray();
                    } else if (peek == JsonToken.BEGIN_OBJECT) {
                        in.beginObject();
                        consumeAll(in);
                        in.endObject();
                    } else if (peek == JsonToken.END_ARRAY) {
                        in.endArray();
                    } else if (peek == JsonToken.END_OBJECT) {
                        in.endObject();
                    } else if (peek == JsonToken.NUMBER) {
                        in.nextString();
                    } else if (peek == JsonToken.BOOLEAN) {
                        in.nextBoolean();
                    } else if (peek == JsonToken.NAME) {
                        in.nextName();
                        consumeAll(in);
                    } else if (peek == JsonToken.NULL) {
                        in.nextNull();
                    }
                }
            }
        };
    }
}

接下來我們來測試一下這個東西起不起作用呢

json數(shù)據(jù)正常的情況下是這樣
main方法

 public static void main(String[] args) {
             String jsonStr="{\"name\":\"Coder\",\"friends\":{\"name\":\"莊長鵬\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

 }

User類

    static class User implements Serializable{
        String name;

        User friends;

        String relation;

        List<User> family;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public User getFriends() {
            return friends;
        }

        public void setFriends(User friends) {
            this.friends = friends;
        }

        public List<User> getFamily() {
            return family;
        }

        public void setFamily(List<User> family) {
            this.family = family;
        }

        public String getRelation() {
            return relation;
        }

        public void setRelation(String relation) {
            this.relation = relation;
        }

        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", friends=" + friends +
                    ", relation='" + relation + '\'' +
                    ", family=" + family +
                    '}';
        }
    }
此時的執(zhí)行結(jié)果為

User{name='Coder', friends=User{name='莊長鵬', friends=null, relation='好朋友', family=null}, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}

情況一

如果此時我們將jsonStr改為這樣,可以看到name明明是個字符串,但是被我改為{}這樣就是object類型了
  public static void main(String[] args) {
        String jsonStr="{\"name\":{},\"friends\":{\"name\":\"莊長鵬\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }
這時就進行解析就拋了異常了
Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected STRING but was BEGIN_OBJECT at line 1 column 85 path $.family
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
    at com.google.gson.Gson.fromJson(Gson.java:927)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)

情況二

我們再將jsonStr改為這樣
    public static void main(String[] args) {
        String jsonStr="{\"name\":\"Coder\",\"friends\":\"\",\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }
此時執(zhí)行又拋異常了
Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 28 path $.friends
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
    at com.google.gson.Gson$FutureTypeAdapter.read(Gson.java:1011)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
    at com.google.gson.Gson.fromJson(Gson.java:927)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)
解析又出錯了,因為User類中的friends是一個object類型,而jsonStr中的friends卻是一個""空字符串

接下來我們使用TypeAdapter來對上述兩種情況進行處理

 public static void main(String[] args) {
        String jsonStr="{\"name\":\"Coder\",\"friends\":\"\",\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
        User json=gson.fromJson(jsonStr,User.class);
//        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }

執(zhí)行結(jié)果為
User{name='Coder', friends=null, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}
嗯 friends雖然類型不匹配,但是并不影響其他字段的解析

我們再對第一種情況進行處理
public static void main(String[] args) {
        String jsonStr="{\"name\":{},\"friends\":{\"name\":\"莊長鵬\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
       User json=gson.fromJson(jsonStr,User.class);
 //       User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }

執(zhí)行的結(jié)果為
User{name='null', friends=User{name='莊長鵬', friends=null, relation='好朋友', family=null}, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}
嗯 json字符串中的name字段雖然變成了{}對象,但是并不影響其他字段的解析

回頭我們來看看

GsonTypeAdapterFactory是怎么處理的呢

  • gson 庫會通過JsonReader對json對象的每個字段進項讀取,當發(fā)現(xiàn)類型不匹配時拋出異常
  • 那么我們就在它拋出異常的時候進行處理,讓它繼續(xù)不中斷接著往下讀取其他的字段就好了
/**
 * Copyright:mjt_pad_android
 * Author: liyang <br>
 * Date:2019/3/4 2:35 PM<br>
 * Desc: <br>
 */
public class GsonTypeAdapterFactory implements TypeAdapterFactory {
    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        final TypeAdapter<T> adapter = gson.getDelegateAdapter(this, type);
        return new TypeAdapter<T>() {
            @Override
            public void write(JsonWriter out, T value) throws IOException {
                adapter.write(out, value);
            }

            @Override
            public T read(JsonReader in) throws IOException {
               //gson 庫會通過JsonReader對json對象的每個字段進項讀取,當發(fā)現(xiàn)類型不匹配時拋出異常
                try {
                    return adapter.read(in);
                } catch (Throwable e) {
                    //那么我們就在它拋出異常的時候進行處理,讓它繼續(xù)不中斷接著往下讀取其他的字段就好了
                    consumeAll(in);
                    return null;
                }

            }

            private void consumeAll(JsonReader in) throws IOException {
                if (in.hasNext()) {
                    JsonToken peek = in.peek();
                    if (peek == JsonToken.STRING) {
                        in.nextString();
                    } else if (peek == JsonToken.BEGIN_ARRAY) {
                        in.beginArray();
                        consumeAll(in);
                        in.endArray();
                    } else if (peek == JsonToken.BEGIN_OBJECT) {
                        in.beginObject();
                        consumeAll(in);
                        in.endObject();
                    } else if (peek == JsonToken.END_ARRAY) {
                        in.endArray();
                    } else if (peek == JsonToken.END_OBJECT) {
                        in.endObject();
                    } else if (peek == JsonToken.NUMBER) {
                        in.nextString();
                    } else if (peek == JsonToken.BOOLEAN) {
                        in.nextBoolean();
                    } else if (peek == JsonToken.NAME) {
                        in.nextName();
                        consumeAll(in);
                    } else if (peek == JsonToken.NULL) {
                        in.nextNull();
                    }
                }
            }
        };
    }
}
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