對List和map等結構的常用轉換操作基本上可以滿足我們處理的絕大多數需求,但有時項目中對json有特殊的格式規定.比如下面的json串解析:
[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":2,"name":"曹贵生","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 9:54:49 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}]
分析之後我們發現普通的方式都不好處理上面的json串.請看本文是如何處理的吧:
實體類:
import java.util.Date; public class Student { private int id; private String name; private Date birthDay; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Date getBirthDay() { return birthDay; } public void setBirthDay(Date birthDay) { this.birthDay = birthDay; } @Override public String toString() { return "Student [birthDay=" + birthDay + ", id=" + id + ", name=" + name + "]"; } } public class Teacher { private int id; private String name; private String title; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } @Override public String toString() { return "Teacher [id=" + id + ", name=" + name + ",]"; } }注意這裡定義了一個TableData實體類:
import java.util.List; public class TableData { private String tableName; private List tableData; public String getTableName() { return tableName; } public void setTableName(String tableName) { this.tableName = tableName; } public List getTableData() { return tableData; } public void setTableData(List tableData) { this.tableData = tableData; } }測試類:
(仔細看將json轉回為對象的實現,這裡經過兩次轉化,第一次轉回的結果是map不是我們所期望的對象,對map再次轉為json後再轉為對象,我引用的是Gson2.1的jar處理正常,好像使用Gson1.6的jar會報錯,所以建議用最新版本)
import java.util.ArrayList; import java.util.Date; import java.util.List; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; public class GsonTest5 { /** * @param args */ public static void main(String[] args) { // 對象轉為Json-->start Student student1 = new Student(); student1.setId(1); student1.setName("李坤"); student1.setBirthDay(new Date()); Student student2 = new Student(); student2.setId(2); student2.setName("曹貴生"); student2.setBirthDay(new Date()); Student student3 = new Student(); student3.setId(3); student3.setName("柳波"); student3.setBirthDay(new Date()); List<Student> stulist = new ArrayList<Student>(); stulist.add(student1); stulist.add(student2); stulist.add(student3); Teacher teacher1 = new Teacher(); teacher1.setId(1); teacher1.setName("米老師"); teacher1.setTitle("教授"); Teacher teacher2 = new Teacher(); teacher2.setId(2); teacher2.setName("丁老師"); teacher2.setTitle("講師"); List<Teacher> teacherList = new ArrayList<Teacher>(); teacherList.add(teacher1); teacherList.add(teacher2); TableData td1 = new TableData(); td1.setTableName("students"); td1.setTableData(stulist); TableData td2 = new TableData(); td2.setTableName("teachers"); td2.setTableData(teacherList); List<TableData> tdList = new ArrayList<TableData>(); tdList.add(td1); tdList.add(td2); Gson gson = new Gson(); String s = gson.toJson(tdList); System.out.println(s); // 結果:[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":2,"name":"曹貴生","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:44:16 AM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老師","title":"教授"},{"id":2,"name":"丁老師","title":"講師"}]}] // 對象轉為Json-->end // ///////////////////////////////////////////////////////////////////// // 將json轉為數據-->start List<TableData> tableDatas2 = gson.fromJson(s, new TypeToken<List<TableData>>() { }.getType()); for (int i = 0; i < tableDatas2.size(); i++) { TableData entityData = tableDatas2.get(i); String tableName = entityData.getTableName(); List tableData = entityData.getTableData(); String s2 = gson.toJson(tableData); // System.out.println(s2); // System.out.println(entityData.getData()); if (tableName.equals("students")) { System.out.println("students"); List<Student> retStuList = gson.fromJson(s2, new TypeToken<List<Student>>() { }.getType()); for (int j = 0; j < retStuList.size(); j++) { System.out.println(retStuList.get(j)); } } else if (tableName.equals("teachers")) { System.out.println("teachers"); List<Teacher> retTchrList = gson.fromJson(s2, new TypeToken<List<Teacher>>() { }.getType()); for (int j = 0; j < retTchrList.size(); j++) { System.out.println(retTchrList.get(j)); } } } // Json轉為對象-->end } }輸出結果:
[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":2,"name":"曹貴生","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:04:12 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老師","title":"教授"},{"id":2,"name":"丁老師","title":"講師"}]}] students Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=1, name=李坤] Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=2, name=曹貴生] Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=3, name=柳波] teachers Teacher [id=1, name=米老師, title=教授] Teacher [id=2, name=丁老師, title=講師]註冊TypeAdapter及處理Enum類型
枚舉類型給我們的程序帶來了好處,如何用Gson來實現與Json的互轉呢?請看本文.
本文重點掌握如何自己寫一個TypeAdapter及註冊TypeAdapter和處理Enum類型.
實體類:
public enum PackageState { PLAY, UPDATE, UPDATING, DOWNLOAD, DOWNLOADING, } public class PackageItem { private String name; private PackageState state; private String size; public String getName() { return name; } public void setName(String name) { this.name = name; } public PackageState getState() { return state; } public void setState(PackageState state) { this.state = state; } public String getSize() { return size; } public void setSize(String size) { this.size = size; } @Override public String toString() { return "PackageItem [name=" + name + ", size=" + size + ", state=" + state + "]"; } }自己寫一個轉換器實現JsonSerializer<T>接口和jsonDeserializer<T>接口:
import java.lang.reflect.Type; import com.google.gson.JsonDeserializationContext; import com.google.gson.JsonDeserializer; import com.google.gson.JsonElement; import com.google.gson.JsonParseException; import com.google.gson.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; public class EnumSerializer implements JsonSerializer<PackageState>, JsonDeserializer<PackageState> { // 對象轉為Json時調用,實現JsonSerializer<PackageState>接口@Override public JsonElement serialize(PackageState state, Type arg1, JsonSerializationContext arg2) { return new JsonPrimitive(state.ordinal()); } // json轉為對象時調用,實現JsonDeserializer<PackageState>接口@Override public PackageState deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { if (json.getAsInt() < PackageState.values().length) return PackageState.values()[json.getAsInt()]; return null; } }測試類:
import com.google.gson.Gson; import com.google.gson.GsonBuilder; public class GsonTest6 { public static void main(String[] args) { GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(PackageState.class, new EnumSerializer()); Gson gson = gsonBuilder.create(); PackageItem item = new PackageItem(); item.setName("item_name"); item.setSize("500M"); item.setState(PackageState.UPDATING);// 這個state是枚舉值String s = gson.toJson(item); System.out.println(s); System.out.println("--------------------------------"); PackageItem retItem = gson.fromJson(s, PackageItem.class); System.out.println(retItem); } }
輸出結果(結果中已經將state的對應枚舉類型轉為了int類型):
{"name":"item_name","state":2,"size":"500M"} -------------------------------- PackageItem [name=item_name, size=500M, state=UPDATING]